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<h1><a class="header" href="#notes" id="notes">Notes</a></h1>
<p>A personal collection of notes and cheatsheets.</p>
<p>Source code is located at <a href="https://github.com/johannst/notes">johannst/notes</a>.</p>
<h1><a class="header" href="#tools" id="tools">Tools</a></h1>
<ul>
<li><a href="tools/./zsh.html">zsh</a></li>
<li><a href="tools/./bash.html">bash</a></li>
<li><a href="tools/./fish.html">fish</a></li>
<li><a href="tools/./tmux.html">tmux</a></li>
<li><a href="tools/./git.html">git</a></li>
<li><a href="tools/./awk.html">awk</a></li>
<li><a href="tools/./emacs.html">emacs</a></li>
<li><a href="tools/./gpg.html">gpg</a></li>
<li><a href="tools/./gdb.html">gdb</a></li>
<li><a href="tools/./radare2.html">radare2</a></li>
<li><a href="tools/./qemu.html">qemu</a></li>
</ul>
<h1><a class="header" href="#zsh1" id="zsh1">zsh(1)</a></h1>
<h2><a class="header" href="#keybindings" id="keybindings">Keybindings</a></h2>
<p>Change input mode:</p>
<pre><code class="language-zsh">bindkey -v change to vi keymap
bindkey -e change to emacs keymap
</code></pre>
<p>Define key-mappings:</p>
<pre><code class="language-zsh">bindkey list mappings in current keymap
bindkey in-str cmd create mapping for `in-str` to `cmd`
bindkey -r in-str remove binding for `in-str`
# C-v <key> dump <key> code, which can be used in `in-str`
# zle -l list all functions for keybindings
# man zshzle(1) STANDARD WIDGETS: get description of functions
</code></pre>
<p>Access edit buffer in zle widget:</p>
<pre><code class="language-zsh">$BUFFER # Entire edit buffer content
$LBUFFER # Edit buffer content left to cursor
$RBUFFER # Edit buffer content right to cursor
# create zle widget which adds text right of the cursor
function add-text() {
RBUFFER="some text $RBUFFER"
}
zle -N add-text
bindkey "^p" add-text
</code></pre>
<h2><a class="header" href="#parameter" id="parameter">Parameter</a></h2>
<p>Default value:</p>
<pre><code class="language-zsh"># default value
echo ${foo:-defval} # defval
foo=bar
echo ${foo:-defval} # bar
</code></pre>
<p>Alternative value:</p>
<pre><code class="language-zsh">echo ${foo:+altval} # ''
foo=bar
echo ${foo:+altval} # altval
</code></pre>
<p>Check variable set, error if not set:</p>
<pre><code class="language-zsh">echo ${foo:?msg} # print `msg` and return errno `1`
foo=bar
echo ${foo:?msg} # bar
</code></pre>
<p>Sub-string <code>${var:offset:length}</code>:</p>
<pre><code class="language-zsh">foo=abcdef
echo ${foo:1:3} # bcd
</code></pre>
<p>Trim prefix <code>${var#prefix}</code>:</p>
<pre><code class="language-zsh">foo=bar.baz
echo ${foo#bar} # .baz
</code></pre>
<p>Trim suffix <code>${var%suffix}</code>:</p>
<pre><code class="language-zsh">foo=bar.baz
echo ${foo%.baz} # bar
</code></pre>
<p>Substitute pattern <code>${var/pattern/replace}</code>:</p>
<pre><code class="language-zsh">foo=aabbccbbdd
echo ${foo/bb/XX} # aaXXccbbdd
echo ${foo//bb/XX} # aaXXccXXdd
# replace prefix
echo ${foo/#bb/XX} # aabbccbbdd
echo ${foo/#aa/XX} # XXbbccbbdd
# replace suffix
echo ${foo/%bb/XX} # aabbccbbdd
echo ${foo/%dd/XX} # aabbccbbXX
</code></pre>
<blockquote>
<p>Note: <code>prefix</code>/<code>suffix</code>/<code>pattern</code> are expanded as pathnames.</p>
</blockquote>
<h2><a class="header" href="#variables" id="variables">Variables</a></h2>
<pre><code class="language-zsh"># Variable with local scope
local var=val
# Read-only variable
readonly var=bal
</code></pre>
<p>Indexed arrays:</p>
<pre><code class="language-zsh">arr=(aa bb cc dd)
echo $arr[1] # aa
echo $arr[-1] # dd
arr+=(ee)
echo $arr[-1] # ee
echo $arr[1,3] # aa bb cc
</code></pre>
<p>Associative arrays:</p>
<pre><code class="language-zsh">typeset -A arr
arr[x]='aa'
arr[y]='bb'
echo $arr[x] # aa
</code></pre>
<p>Tied arrays:</p>
<pre><code class="language-zsh">typeset -T VEC vec=(1 2 3) '|'
echo $vec # 1 2 3
echo $VEC # 1|2|3
</code></pre>
<p>Unique arrays (set):</p>
<pre><code>typeset -U vec=(1 2 3)
echo $vec # 1 2 3
vec+=(1 2 4)
echo $vec # 1 2 3 4
</code></pre>
<h3><a class="header" href="#expansion-flags" id="expansion-flags">Expansion Flags</a></h3>
<p>Join array to string <code>j:sep:</code>:</p>
<pre><code class="language-zsh">foo=(1 2 3 4)
echo ${(j:-:)foo} # 1-2-3-4
echo ${(j:\n:)foo} # join with new lines
</code></pre>
<p>Split string to array <code>s:sep</code>:</p>
<pre><code class="language-zsh">foo='1-2-3-4'
bar=(${(s:-:)foo}) # capture as array
echo $bar # 1 2 3 4
echo $bar[2] # 2
</code></pre>
<p>Upper/Lower case string:</p>
<pre><code class="language-zsh">foo=aaBB
echo ${(L)foo} # aabb
echo ${(U)foo} # AABB
</code></pre>
<h2><a class="header" href="#argument-parsing-with-zparseopts" id="argument-parsing-with-zparseopts">Argument parsing with <code>zparseopts</code></a></h2>
<pre><code class="language-zsh">zparseopts [-D] [-E] [-A assoc] specs
</code></pre>
<p>Arguments are copied into the associative array <code>assoc</code> according to <code>specs</code>.
Each spec is described by an entry as <code>opt[:][=array]</code>.</p>
<ul>
<li><code>opt</code> is the option without the <code>-</code> char. Passing <code>-f</code> is matched against <code>f</code>
opt, <code>--long</code> is matched against <code>-long</code>.</li>
<li>Using <code>:</code> means the option will take an argument.</li>
<li>The optional <code>=array</code> specifies an alternate storage container where this
option should be stored.</li>
</ul>
<blockquote>
<p>Documentation can be found in <code>man zshmodules</code>.</p>
</blockquote>
<h3><a class="header" href="#example" id="example">Example</a></h3>
<pre><code class="language-zsh">#!/bin/zsh
function test() {
zparseopts -D -E -A opts f=flag o: -long:
echo "flag $flag"
echo "o $opts[-o]"
echo "long $opts[--long]"
echo "pos $1"
}
test -f -o OPTION --long LONG_OPT POSITIONAL
# Outputs:
# flag -f
# o OPTION
# long LONG_OPT
# pos POSITIONAL
</code></pre>
<h2><a class="header" href="#regular-expressions" id="regular-expressions">Regular Expressions</a></h2>
<p>Zsh supports regular expression matching with the binary operator <code>=~</code>.
The match results can be accessed via the <code>$MATCH</code> variable and
<code>$match</code> indexed array:</p>
<ul>
<li><code>$MATCH</code> contains the full match</li>
<li><code>$match[1]</code> contains match of the first capture group</li>
</ul>
<pre><code class="language-zsh">INPUT='title foo : 1234'
REGEX='^title (.+) : ([0-9]+)$'
if [[ $INPUT =~ $REGEX ]]; then
echo "$MATCH" # title foo : 1234
echo "$match[1]" # foo
echo "$match[2]" # 1234
fi
</code></pre>
<h2><a class="header" href="#completion" id="completion">Completion</a></h2>
<h3><a class="header" href="#installation" id="installation">Installation</a></h3>
<p>Completion functions are provided via files and need to be placed in a location
covered by <code>$fpath</code>. By convention the completion files are names as <code>_<CMD></code>.</p>
<p>A completion skeleton for the command <code>foo</code>, stored in <code>_foo</code></p>
<pre><code class="language-zsh">#compdef _foo foo
function _foo() {
...
}
</code></pre>
<p>Alternatively one can install a completion function explicitly by calling <code>compdef <FUNC> <CMD></code>.</p>
<h3><a class="header" href="#completion-variables" id="completion-variables">Completion Variables</a></h3>
<p>Following variables are available in Completion functions:</p>
<pre><code class="language-zsh">$words # array with command line in words
$#words # number words
$CURRENT # index into $words for cursor position
$words[CURRENT-1] # previous word (relative to cursor position)
</code></pre>
<h3><a class="header" href="#completion-functions" id="completion-functions">Completion Functions</a></h3>
<ul>
<li><code>_describe</code> simple completion, just words + description</li>
<li><code>_arguments</code> sophisticated completion, allow to specify actions</li>
</ul>
<h4><a class="header" href="#completion-with-a-hrefhttpzshsourceforgenetdocreleasecompletion-systemhtmlcompletion-functions_describea" id="completion-with-a-hrefhttpzshsourceforgenetdocreleasecompletion-systemhtmlcompletion-functions_describea">Completion with <a href="http://zsh.sourceforge.net/Doc/Release/Completion-System.html#Completion-Functions"><code>_describe</code></a></a></h4>
<pre><code class="language-zsh">_describe MSG COMP
</code></pre>
<ul>
<li><code>MSG</code> simple string with header message</li>
<li><code>COMP</code> array of completions where each entry is <code>"opt:description"</code></li>
</ul>
<pre><code class="language-zsh">function _foo() {
local -a opts
opts=('bla:desc for bla' 'blu:desc for blu')
_describe 'foo-msg' opts
}
compdef _foo foo
foo <TAB><TAB>
-- foo-msg --
bla -- desc for bla
blu -- desc for blu
</code></pre>
<h4><a class="header" href="#completion-with-a-hrefhttpzshsourceforgenetdocreleasecompletion-systemhtmlcompletion-functions_argumentsa" id="completion-with-a-hrefhttpzshsourceforgenetdocreleasecompletion-systemhtmlcompletion-functions_argumentsa">Completion with <a href="http://zsh.sourceforge.net/Doc/Release/Completion-System.html#Completion-Functions"><code>_arguments</code></a></a></h4>
<pre><code class="language-zsh">_arguments SPEC [SPEC...]
</code></pre>
<p>where <code>SPEC</code> can have one of the following forms:</p>
<ul>
<li><code>OPT[DESC]:MSG:ACTION</code></li>
<li><code>N:MSG:ACTION</code></li>
</ul>
<p>Available actions</p>
<pre><code class="language-zsh">(op1 op2) list possible matches
->VAL set $state=VAL and continue, `$state` can be checked later in switch case
FUNC call func to generate matches
{STR} evaluate `STR` to generate matches
</code></pre>
<h3><a class="header" href="#example-1" id="example-1">Example</a></h3>
<p>Skeleton to copy/paste for writing simple completions.</p>
<p>Assume a program <code>foo</code> with the following interface:</p>
<pre><code class="language-zsh">foo -c green|red|blue -s low|high -f <file> -d <dir> -h
</code></pre>
<p>The completion handler could be implemented as follows in a file called <code>_foo</code>:</p>
<pre><code class="language-zsh">#compdef _foo foo
function _foo_color() {
local colors=()
colors+=('green:green color')
colors+=('red:red color')
colors+=('blue:blue color')
_describe "color" colors
}
function _foo() {
_arguments \
"-c[define color]:color:->s_color" \
"-s[select sound]:sound:(low high)" \
"-f[select file]:file:_files" \
"-d[select dir]:dir:_files -/" \
"-h[help]"
case $state in
s_color) _foo_color;;
esac
}
</code></pre>
<blockquote>
<p><code>_files</code> is a zsh builtin utility function to complete files/dirs see</p>
<ul>
<li><a href="http://zsh.sourceforge.net/Doc/Release/Completion-System.html#Completion-Functions">zsh completion functions</a></li>
<li><a href="https://github.com/zsh-users/zsh-completions/blob/master/zsh-completions-howto.org#utility-functions">zsh completion utility functions</a></li>
</ul>
</blockquote>
<h1><a class="header" href="#bash1" id="bash1">bash(1)</a></h1>
<h2><a class="header" href="#expansion" id="expansion">Expansion</a></h2>
<h3><a class="header" href="#generator" id="generator">Generator</a></h3>
<pre><code class="language-bash"># generate sequence from n to m
{n..m}
# generate sequence from n to m step by s
{n..m..s}
# expand cartesian product
{a,b}{c,d}
</code></pre>
<h3><a class="header" href="#parameter-1" id="parameter-1">Parameter</a></h3>
<pre><code class="language-bash"># default value
bar=${foo:-some_val} # if $foo set, then bar=$foo else bar=some_val
# alternate value
bar=${foo:+bla $foo} # if $foo set, then bar="bla $foo" else bar=""
# check param set
bar=${foo:?msg} # if $foo set, then bar=$foo else exit and print msg
# indirect
FOO=foo
BAR=FOO
bar=${!BAR} # deref value of BAR -> bar=$FOO
# prefix
${foo#prefix} # remove prefix when expanding $foo
# suffix
${foo%suffix} # remove suffix when expanding $foo
# substitute
${foo/pattern/string} # replace pattern with string when expanding foo
# pattern starts with
# '/' replace all occurences of pattern
# '#' pattern match at beginning
# '%' pattern match at end
</code></pre>
<blockquote>
<p>Note: <code>prefix</code>/<code>suffix</code>/<code>pattern</code> are expanded as <a href="tools/bash.html#pathname">pathnames</a>.</p>
</blockquote>
<h3><a class="header" href="#pathname" id="pathname">Pathname</a></h3>
<pre><code class="language-bash">* match any string
? match any single char
\\ match backslash
[abc] match any char of 'a' 'b' 'c'
[a-z] match any char between 'a' - 'z'
[^ab] negate, match all not 'a' 'b'
[:class:] match any char in class, available:
alnum,alpha,ascii,blank,cntrl,digit,graph,lower,
print,punct,space,upper,word,xdigit
</code></pre>
<p>Wit <code>extglob</code> shell option enabled it is possible to have more powerful
patterns. In the following <code>pattern-list</code> is one ore more patterns separated
by <code>|</code> char.</p>
<pre><code class="language-bash">?(pattern-list) matches zero or one occurrence of the given patterns
*(pattern-list) matches zero or more occurrences of the given patterns
+(pattern-list) matches one or more occurrences of the given patterns
@(pattern-list) matches one of the given patterns
!(pattern-list) matches anything except one of the given patterns
</code></pre>
<blockquote>
<p>Note: <code>shopt -s extglob</code>/<code>shopt -u extglob</code> to enable/disable <code>extglob</code>
option.</p>
</blockquote>
<h2><a class="header" href="#io-redirection" id="io-redirection">I/O redirection</a></h2>
<blockquote>
<p>Note: The trick with bash I/O redirection is to interpret from left-to-right.</p>
</blockquote>
<pre><code class="language-bash"># stdout & stderr to file
command >file 2>&1
# equivalent
command &>file
# stderr to stdout & stdout to file
command 2>&1 >file
</code></pre>
<h3><a class="header" href="#explanation" id="explanation">Explanation</a></h3>
<pre><code class="language-bash">j>&i
</code></pre>
<p>Duplicate <code>fd i</code> to <code>fd j</code>, making <code>j</code> a copy of <code>i</code>. See <a href="http://man7.org/linux/man-pages/man2/dup.2.html">dup2(2)</a>.</p>
<p>Example:</p>
<pre><code class="language-bash">command 2>&1 >file
</code></pre>
<ol>
<li>duplicate <code>fd 1</code> to <code>fd 2</code>, effectively redirecting <code>stderr</code> to <code>stdout</code></li>
<li>redirect <code>stdout</code> to <code>file</code></li>
</ol>
<h2><a class="header" href="#argument-parsing-with-getopts" id="argument-parsing-with-getopts">Argument parsing with <code>getopts</code></a></h2>
<p>The <code>getopts</code> builtin uses following global variables:</p>
<ul>
<li><code>OPTARG</code>, value of last option argument</li>
<li><code>OPTIND</code>, index of the next argument to process (user must reset)</li>
<li><code>OPTERR</code>, display errors if set to <code>1</code></li>
</ul>
<pre><code class="language-bash">getopts <optstring> <param> [<args>]
</code></pre>
<ul>
<li><code><optstring></code> specifies the names of supported options, eg <code>f:c</code>
<ul>
<li><code>f:</code> means <code>-f</code> option with an argument</li>
<li><code>c</code> means <code>-c</code> option without an argument</li>
</ul>
</li>
<li><code><param></code> specifies a variable name which <code>getopts</code> fills with the last parsed option argument</li>
<li><code><args></code> optionally specify argument string to parse, by default <code>getopts</code> parses <code>$@</code></li>
</ul>
<h3><a class="header" href="#example-2" id="example-2">Example</a></h3>
<pre><code class="language-bash">#!/bin/bash
function parse_args() {
while getopts "f:c" PARAM; do
case $PARAM in
f) echo "GOT -f $OPTARG";;
c) echo "GOT -c";;
*) echo "ERR: print usage"; exit 1;;
esac
done
# users responsibility to reset OPTIND
OPTIND=1
}
parse_args -f xxx -c
parse_args -f yyy
</code></pre>
<h2><a class="header" href="#regular-expressions-1" id="regular-expressions-1">Regular Expressions</a></h2>
<p>Bash supports regular expression matching with the binary operator <code>=~</code>.
The match results can be accessed via the <code>$BASH_REMATCH</code> variable:</p>
<ul>
<li><code>${BASH_REMATCH[0]}</code> contains the full match</li>
<li><code>${BASH_REMATCH[1]}</code> contains match of the first capture group</li>
</ul>
<pre><code class="language-bash">INPUT='title foo : 1234'
REGEX='^title (.+) : ([0-9]+)$'
if [[ $INPUT =~ $REGEX ]]; then
echo "${BASH_REMATCH[0]}" # title foo : 1234
echo "${BASH_REMATCH[1]}" # foo
echo "${BASH_REMATCH[2]}" # 1234
fi
</code></pre>
<blockquote>
<p><strong>Caution</strong>: When specifying a <code>regex</code> in the <code>[[ ]]</code> block directly, quotes will be treated as part of the pattern.
<code>[[ $INPUT =~ "foo" ]]</code> will match against <code>"foo"</code> not <code>foo</code>!</p>
</blockquote>
<h2><a class="header" href="#completion-1" id="completion-1">Completion</a></h2>
<p>The <code>complete</code> builtin is used to interact with the completion system.</p>
<pre><code class="language-bash">complete # print currently installed completion handler
complete -F <func> <cmd> # install <func> as completion handler for <cmd>
complete -r <cmd> # uninstall completion handler for <cmd>
</code></pre>
<p>Variables available in completion functions:</p>
<pre><code class="language-bash"># in
$1 # <cmd>
$2 # current word
$3 # privous word
COMP_WORDS # array with current command line words
COMP_CWORD # index into COMP_WORDS with current cursor position
# out
COMPREPLY # array with possible completions
</code></pre>
<p>The <code>compgen</code> builtin is used to generate possible matches by comparing <code>word</code>
against words generated by <code>option</code>.</p>
<pre><code class="language-bash">compgen <option> <word>
# usefule options:
# -W <list> specify list of possible completions
# -d generate list with dirs
# -f generate list with files
# -u generate list with users
# -e generate list with exported variables
# compare "f" against words "foo" "foobar" "bar" and generate matches
compgen -W "foo foobar bar" "f"
# compare "hom" against file/dir names and generate matches
compgen -d -f "hom"
</code></pre>
<h3><a class="header" href="#example-3" id="example-3">Example</a></h3>
<p>Skeleton to copy/paste for writing simple completions.</p>
<p>Assume a program <code>foo</code> with the following interface:</p>
<pre><code class="language-bash">foo -c green|red|blue -s low|high -f <file> -h
</code></pre>
<p>The completion handler could be implemented as follows:</p>
<pre><code class="language-bash">function _foo() {
local curr=$2
local prev=$3
local opts="-c -s -f -h"
case $prev in
-c) COMPREPLY=( $(compgen -W "green red blue" -- $curr) );;
-s) COMPREPLY=( $(compgen -W "low high" -- $curr) );;
-f) COMPREPLY=( $(compgen -f -- $curr) );;
*) COMPREPLY=( $(compgen -W "$opts" -- $curr) );;
esac
}
complete -F _foo foo
</code></pre>
<h1><a class="header" href="#fish1" id="fish1">fish(1)</a></h1>
<h2><a class="header" href="#quick-info" id="quick-info">Quick Info</a></h2>
<p>Fish initialization file <code>~/.config/fish/config.fish</code></p>
<p>Switch between different key bindings:</p>
<ul>
<li><code>fish_default_key_bindings</code> to use default key bindings</li>
<li><code>fish_vi_key_bindings</code> to use vi key bindings</li>
</ul>
<h2><a class="header" href="#variables-1" id="variables-1">Variables</a></h2>
<p>Available scopes</p>
<ul>
<li><code>local</code> variable local to a block</li>
<li><code>global</code> variable global to shell instance</li>
<li><code>universal</code> variable universal to all shell instances + preserved across
shell restart</li>
</ul>
<h3><a class="header" href="#setunset-variables" id="setunset-variables">Set/Unset Variables</a></h3>
<pre><code class="language-text">set <name> [<values>]
-l local scope
-g global scope
-U universal scope
-e erase variable
-S show verbose info
-x export to ENV
-u unexport from ENV
</code></pre>
<h3><a class="header" href="#lists" id="lists">Lists</a></h3>
<p>In <code>fish</code> all variables are lists (start with index <code>1</code>, but lists can't
contain lists.</p>
<pre><code class="language-text">set foo a b c d
echo $foo[1] # a
echo $foo[-1] # d
echo $foo[2..3] # b c
echo $foo[1 3] # a c
</code></pre>
<p><code>$</code> can be seen as dereference operator.</p>
<pre><code class="language-text">set foo a; set a 1337
echo $$foo # outputs 1337
</code></pre>
<p>Cartesian product.</p>
<pre><code class="language-text">echo file.{h,cc}
# file.h file.cc
echo {a,b}{1,2}
# a1 b1 b2
</code></pre>
<h3><a class="header" href="#special-variables-lists" id="special-variables-lists">Special Variables (Lists)</a></h3>
<pre><code class="language-text">$status # exit code of last command
$pipestatus # list of exit codes of pipe chain
$CMD_DURATION # runtime of last command in ms
</code></pre>
<h4><a class="header" href="#path" id="path"><code>*PATH</code></a></h4>
<p>Lists ending with <code>PATH</code> are automatically split at <code>:</code> when used and joined
with <code>:</code> when exported to the environment.</p>
<pre><code class="language-text">set -x BLA_PATH a:b:c:d
echo $BLA_PATH # a b c d
env | grep BLA_PATH # BLA_PATH=a:b:c:d
</code></pre>
<h2><a class="header" href="#command-handling" id="command-handling">Command Handling</a></h2>
<pre><code class="language-text"># sub-commands are not run in quotes
echo "ls output: "(ls)
</code></pre>
<h3><a class="header" href="#io-redirection-1" id="io-redirection-1">I/O redirection</a></h3>
<pre><code class="language-text"># 'noclobber', fail if 'log' already exists
echo foo >? log
</code></pre>
<h2><a class="header" href="#control-flow" id="control-flow">Control Flow</a></h2>
<h3><a class="header" href="#if--else" id="if--else"><code>if</code> / <code>else</code></a></h3>
<pre><code class="language-text">if grep foo bar
# do sth
else if grep foobar bar
# do sth else
else
# do sth else
end
</code></pre>
<h3><a class="header" href="#switch" id="switch"><code>switch</code></a></h3>
<pre><code class="language-text">switch (echo foo)
case 'foo*'
# do start with foo
case bar dudel
# do bar and dudel
case '*'
# do else
end
</code></pre>
<h3><a class="header" href="#while-loop" id="while-loop"><code>while</code> Loop</a></h3>
<pre><code class="language-text">while true
echo foo
end
</code></pre>
<h3><a class="header" href="#for-loop" id="for-loop"><code>for</code> Loop</a></h3>
<pre><code class="language-text">for f in (ls)
echo $f
end
</code></pre>
<h2><a class="header" href="#functions" id="functions">Functions</a></h2>
<p>Function arguments are passed via <code>$argv</code> list.</p>
<pre><code class="language-text">function fn_foo
echo $argv
end
</code></pre>
<h3><a class="header" href="#autoloading" id="autoloading">Autoloading</a></h3>
<p>When running a command fish attempts to autoload a function. The shell looks
for <code><cmd>.fish</code> in the locations defined by <code>$fish_function_path</code> and loads
the function lazily if found.</p>
<p>This is the preferred way over monolithically defining all functions in a
startup script.</p>
<h3><a class="header" href="#helper" id="helper">Helper</a></h3>
<pre><code class="language-text">functions # list al functions
functions foo # describe function 'foo'
functions -e foo # erase function 'foo'
funced foo # edit function 'foo'
# '-e vim' to edit in vim
</code></pre>
<h2><a class="header" href="#prompt" id="prompt">Prompt</a></h2>
<p>The prompt is defined by the output of the <code>fish_prompt</code> function.</p>
<pre><code class="language-text">function fish_prompt
set -l cmd_ret
echo "> "(pwd) $cmd_ret" "
end
</code></pre>
<blockquote>
<p>Use <code>set_color</code> to manipulate terminal colors.</p>
</blockquote>
<h2><a class="header" href="#useful-builtins" id="useful-builtins">Useful Builtins</a></h2>
<pre><code class="language-text"># history
history search <str> # search history for <str>
history merge # merge histories from fish sessions
# list
count $var # count elements in list
# string
string split SEP STRING
</code></pre>
<h2><a class="header" href="#keymaps" id="keymaps">Keymaps</a></h2>
<pre><code class="language-text"> Shift-Tab ........... tab-completion with search
Alt-Up / Alt-Down ... search history with token under the cursor
Alt-l ............... list content of dir under cursor
Alt-p ............... append '2>&1 | less;' to current cmdline
</code></pre>
<h2><a class="header" href="#debug" id="debug">Debug</a></h2>
<pre><code class="language-text"> status print-stack-trace .. prints function stacktrace (can be used in scripts)
breakpoint ................ halt script execution and gives shell (C-d | exit
to continue)
</code></pre>
<h1><a class="header" href="#tmux1" id="tmux1">tmux(1)</a></h1>
<p>Terminology:</p>
<ul>
<li><code>session</code> is a collection of pseudo terminals which can have multiple
<code>windows</code></li>
<li><code>window</code> uses the entire screen and can be split into rectangular <code>panes</code></li>
<li><code>pane</code> is a single pseudo terminal instance</li>
</ul>
<h1><a class="header" href="#tmux-cli" id="tmux-cli">Tmux cli</a></h1>
<pre><code class="language-markdown"># Session
tmux creates new session
tmux ls list running sessions
tmux kill-session -t <s> kill running session <s>
tmux attach -t <s> [-d] attach to session <s>, detach other clients [-d]
tmux detach -s <s> detach all clients from session <s>
# Environment
tmux showenv -g show global tmux environment variables
tmux setenv -g <var> <val> set variable in global tmux env
# Misc
tmux source-file <file> source config <file>
tmux lscm list available tmux commnds
tmux show -g show global tmux options
tmux display <msg> display message in tmux status line
</code></pre>
<h2><a class="header" href="#scripting" id="scripting">Scripting</a></h2>
<pre><code class="language-markdown"># Session
tmux list-sessions -F '#S' list running sessions, only IDs
# Window
tmux list-windows -F '#I' -t <s> list window IDs for session <s>
tmux selectw -t <s>:<w> select window <w> in session <s>
# Pane
tmux list-panes -F '#P' -t <s>:<w> list pane IDs for window <w> in session <s>
tmux selectp -t <s>:<w>.<p> select pane <p> in window <w> in session <s>
# Run commands
tmux send -t <s>:<w>.<p> "ls" C-m send cmds/keys to pane
tmux run -t <p> <sh-cmd> run shell command <sh-cmd> in background and report output on pane -t <p>
</code></pre>
<p>For example cycle through all panes in all windows in all sessions:</p>
<pre><code class="language-bash"># bash
for s in $(tmux list-sessions -F '#S'); do
for w in $(tmux list-windows -F '#I' -t $s); do
for p in $(tmux list-panes -F '#P' -t $s:$w); do
echo $s:$w.$p
done
done
done
</code></pre>
<h1><a class="header" href="#bindings" id="bindings">Bindings</a></h1>
<pre><code class="language-markdown">prefix d detach from current session
prefix c create new window
prefix w open window list
prefix $ rename session
prefix , rename window
prefix . move current window
</code></pre>
<p>Following bindings are specific to my <a href="https://github.com/johannst/dotfiles/blob/master/tmux.conf"><code>tmux.conf</code></a>:</p>
<pre><code class="language-markdown">C-s prefix
# Panes
prefix s horizontal split
prefix v vertical split
prefix f toggle maximize/minimize current pane
# Movement
prefix Tab toggle between window
prefix h move to pane left
prefix j move to pane down
prefix k move to pane up
prefix l move to pane right
# Resize
prefix C-h resize pane left
prefix C-j resize pane down
prefix C-k resize pane up
prefix C-l resize pane right
# Copy/Paste
prefix C-v enter copy mode
prefix C-p paste yanked text
prefix C-b open copy-buffer list
# In Copy Mode
v enable visual mode
y yank selected text
</code></pre>
<h1><a class="header" href="#command-mode" id="command-mode">Command mode</a></h1>
<p>To enter command mode <code>prefix :</code>.</p>
<p>Some useful commands are:</p>
<pre><code class="language-markdown">setw synchronize-panes on/off enables/disables synchronized input to all panes
list-keys -t vi-copy list keymaps for vi-copy mode
</code></pre>
<h1><a class="header" href="#git1" id="git1">git(1)</a></h1>
<h2><a class="header" href="#staging" id="staging">staging</a></h2>
<pre><code class="language-markdown"> git add -p [<file>] ............ partial staging (interactive)
</code></pre>
<h2><a class="header" href="#remote" id="remote">Remote</a></h2>
<pre><code class="language-markdown"> git remote -v .................. list remotes verbose (with URLs)
git remote show [-n] <remote> .. list info for <remote> (like remote HEAD,
remote branches, tracking mapping)
</code></pre>
<h2><a class="header" href="#branching" id="branching">Branching</a></h2>
<pre><code class="language-markdown"> git branch [-a] ................ list available branches; -a to include
remote branches
git branch -vv ................. list branch & annotate with head sha1 &
remote tracking branch
git branch <bname> ............. create branch with name <bname>
git checkout <bname> ........... switch to branch with name <bname>
git checkout --track <branch> .. start to locally track a remote branch
git push -u origin <rbname> .... push branch to origin (or other remote), and
setup <rbname> as tracking branch
</code></pre>
<h2><a class="header" href="#resetting" id="resetting">Resetting</a></h2>
<pre><code class="language-markdown"> git reset [opt] <ref|commit>
opt:
--mixed .................... resets index, but not working tree
--hard ..................... matches the working tree and index to that
of the tree being switched to any changes to
tracked files in the working tree since
<commit> are lost
git reset HEAD <file> .......... remove file from staging
git reset --soft HEAD~1 ........ delete most recent commit but keep work
git reset --hard HEAD~1 ........ delete most recent commit and delete work
</code></pre>
<h2><a class="header" href="#tags" id="tags">Tags</a></h2>
<pre><code class="language-markdown"> git tag -a <tname> -m "descr" ........ creates an annotated tag (full object
containing tagger, date, ...)
git tag -l ........................... list available tags
git checkout tag/<tname> ............. checkout specific tag
git checkout tag/<tname> -b <bname> .. checkout specific tag in a new branch
</code></pre>
<h2><a class="header" href="#diff" id="diff">Diff</a></h2>
<pre><code class="language-markdown"> git diff HEAD:<fname> origin/HEAD:<fname> ... diff files for different refs
git diff -U$(wc -l <fname>) <fname> ......... shows complete file with diffs
instead of usual diff snippets
</code></pre>
<h2><a class="header" href="#log" id="log">Log</a></h2>
<pre><code class="language-markdown"> git log --oneline .... shows log in single line per commit -> alias for
'--pretty=oneline --abbrev-commit'
git log --graph ...... text based graph of commit history
git log --decorate ... decorate log with REFs
</code></pre>
<h2><a class="header" href="#file-history" id="file-history">File history</a></h2>
<pre><code class="language-markdown"> git log -p <file> ......... show commit history + diffs for <file>
git log --oneline <file> .. show commit history for <file> in compact format
</code></pre>
<h2><a class="header" href="#patching" id="patching">Patching</a></h2>
<pre><code class="language-markdown"> git format-patch <opt> <since>/<revision range>
opt:
-N ................... use [PATCH] instead [PATCH n/m] in subject when
generating patch description (for patches spanning
multiple commits)
--start-number <n> ... start output file generation with <n> as start
number instead '1'
since spcifier:
-3 .................. e.g: create a patch from last three commits
<commit hash> ....... create patch with commits starting after <commit hash>
git am <patch> ......... apply patch and create a commit for it
git apply --stat <PATCH> ... see which files the patch would change
git apply --check <PATCH> .. see if the patch can be applied cleanly
git apply <PATCH> .......... apply the patch locally without creating a commit
# eg: generate patches for each commit from initial commit on
git format-patch -N $(git rev-list --max-parents=0 HEAD)
# generate single patch file from a certain commit/ref
git format-patch <COMMIT/REF> --stdout > my-patch.patch
</code></pre>
<h2><a class="header" href="#submodules" id="submodules">Submodules</a></h2>
<pre><code class="language-markdown"> git submodule add <url> [<path>] .......... add new submodule to current project
git clone --recursive <url> ............... clone project and recursively all
submodules (same as using
'git submodule update --init
--recursive' after clone)
git submodule update --init --recursive ... checkout submodules recursively
using the commit listed in the
super-project (in detached HEAD)
git submodule update --remote <submod> .... fetch & merge remote changes for
<submod>, this will pull
origin/HEAD or a branch specified
for the submodule
git diff --submodule ...................... show commits that are part of the
submodule diff
</code></pre>
<h2><a class="header" href="#inspection" id="inspection">Inspection</a></h2>
<pre><code class="language-markdown"> git ls-tree [-r] <ref> .... show git tree for <ref>, -r to recursively ls sub-trees
git show <obj> ............ show <obj>
git cat-file -p <obj> ..... print content of <obj>
</code></pre>
<h2><a class="header" href="#revision-specifier" id="revision-specifier">Revision Specifier</a></h2>
<pre><code class="language-markdown"> HEAD ........ last commit
HEAD~1 ...... last commit-1
HEAD~N ...... last commit-N (linear backwards when in tree structure, check
difference between HEAD^ and HEAD~)
git rev-list --max-parents=0 HEAD ........... first commit
</code></pre>
<h1><a class="header" href="#awk1" id="awk1">awk(1)</a></h1>
<pre><code class="language-markdown">awk [opt] program [input]
-F <sepstr> field separator string (can be regex)
program awk program
input file or stdin if not file given
</code></pre>
<h2><a class="header" href="#input-processing" id="input-processing">Input processing</a></h2>
<p>Input is processed in two stages:</p>
<ol>
<li>Splitting input into a sequence of <code>records</code>.
By default split at <code>newline</code> character, but can be changed via the
builtin <code>RS</code> variable.</li>
<li>Splitting a <code>record</code> into <code>fields</code>. By default strings without <code>whitespace</code>,
but can be changed via the builtin variable <code>FS</code> or command line option
<code>-F</code>.</li>
</ol>
<p>Fields are accessed as follows:</p>
<ul>
<li><code>$0</code> whole <code>record</code></li>
<li><code>$1</code> field one</li>
<li><code>$2</code> field two</li>
<li>...</li>
</ul>
<h2><a class="header" href="#program" id="program">Program</a></h2>
<p>An <code>awk</code> program is composed of pairs of the form:</p>
<pre><code class="language-markdown">pattern { action }
</code></pre>
<p>The program is run against each <code>record</code> in the input stream. If a <code>pattern</code>
matches a <code>record</code> the corresponding <code>action</code> is executed and can access the
<code>fields</code>.</p>
<pre><code class="language-markdown">INPUT
|
v
record ----> ∀ pattern matched
| |
v v
fields ----> run associated action
</code></pre>
<p>Any valid awk <code>expr</code> can be a <code>pattern</code>.</p>
<h3><a class="header" href="#special-pattern" id="special-pattern">Special pattern</a></h3>
<p>awk provides two special patterns, <code>BEGIN</code> and <code>END</code>, which can be used
multiple times. Actions with those patterns are <strong>executed exactly once</strong>.</p>
<ul>
<li><code>BEGIN</code> actions are run before processing the first record</li>
<li><code>END</code> actions are run after processing the last record</li>
</ul>
<h3><a class="header" href="#special-variables" id="special-variables">Special variables</a></h3>
<ul>
<li><code>RS</code> <em>record separator</em>: first char is the record separator, by default
<newline></li>
<li><code>FS</code> <em>field separator</em>: regex to split records into fields, by default
<space></li>
<li><code>NR</code> <em>number record</em>: number of current record</li>
<li><code>NF</code> <em>number fields</em>: number of fields in the current record</li>
</ul>
<h3><a class="header" href="#special-statements--functions" id="special-statements--functions">Special statements & functions</a></h3>
<ul>
<li>
<p><code>printf "fmt", args...</code></p>
<p>Print format string, args are comma separated.</p>
<ul>
<li><code>%s</code> string</li>
<li><code>%d</code> decimal</li>
<li><code>%x</code> hex</li>
<li><code>%f</code> float</li>
</ul>
<p>Width can be specified as <code>%Ns</code>, this reserves <code>N</code> chars for a string.
For floats one can use <code>%N.Mf</code>, <code>N</code> is the total number including <code>.</code> and
<code>M</code>.</p>
</li>
<li>
<p><code>strftime("fmt")</code></p>
<p>Print time stamp formatted by <code>fmt</code>.</p>
<ul>
<li><code>%Y</code> full year (eg 2020)</li>
<li><code>%m</code> month (01-12)</li>
<li><code>%d</code> day (01-31)</li>
<li><code>%F</code> alias for <code>%Y-%m-%d</code></li>
<li><code>%H</code> hour (00-23)</li>
<li><code>%M</code> minute (00-59)</li>
<li><code>%S</code> second (00-59)</li>
<li><code>%T</code> alias for <code>%H:%M:%S</code></li>
</ul>
</li>
</ul>
<h2><a class="header" href="#examples" id="examples">Examples</a></h2>
<h3><a class="header" href="#filter-records" id="filter-records">Filter records</a></h3>
<pre><code class="language-bash">awk 'NR%2 == 0 { print $0 }' <file>
</code></pre>
<p>The pattern <code>NR%2 == 0</code> matches every second record and the action <code>{ print $0 }</code>
prints the whole record.</p>
<h3><a class="header" href="#access-last-fields-in-records" id="access-last-fields-in-records">Access last fields in records</a></h3>
<pre><code class="language-bash">echo 'a b c d e f' | awk '{ print $NF $(NF-1) }'
</code></pre>
<p>Access last fields with arithmetic on the <code>NR</code> number of fields variable.</p>
<h3><a class="header" href="#capture-in-variables" id="capture-in-variables">Capture in variables</a></h3>
<pre><code class="language-bash"># /proc/<pid>/status
# Name: cat
# ...
# VmRSS: 516 kB
# ...
for f in /proc/*/status; do
cat $f | awk '
/^VmRSS/ { rss = $2/1024 }
/^Name/ { name = $2 }
END { printf "%16s %6d MB\n", name, rss }';
done | sort -k2 -n
</code></pre>
<p>We capture values from <code>VmRSS</code> and <code>Name</code> into variables and print them at the
<code>END</code> once processing all records is done.</p>
<h3><a class="header" href="#run-shell-command-and-capture-output" id="run-shell-command-and-capture-output">Run shell command and capture output</a></h3>
<pre><code class="language-bash">cat /proc/1/status | awk '
/^Pid/ {
"ps --no-header -o user " $2 | getline user;
print user
}'
</code></pre>
<p>We build a <code>ps</code> command line and capture the first line of the processes output
in the <code>user</code> variable and then print it.</p>
<h1><a class="header" href="#emacs1" id="emacs1">emacs(1)</a></h1>
<h2><a class="header" href="#help" id="help">help</a></h2>
<pre><code class="language-markdown"> C-h ? list available help modes
C-h e show message output (`*Messages*` buffer)
C-h f describe function
C-h v describe variable
C-h w describe which key invoke function (where-is)
C-h c <KEY> print command bound to <KEY>
C-h k <KEY> describe command bound to <KEY>
C-h b list buffer local key-bindings
<kseq> C-h list possible key-bindings with <kseq>
eg C-x C-h -> list key-bindings beginning with C-x
</code></pre>
<h2><a class="header" href="#package-manager" id="package-manager">package manager</a></h2>
<pre><code class="language-markdown"> key fn description
------------------------------------------------
package-refresh-contents refresh package list
package-list-packages list available/installed packages
`U x` to mark packages for Upgrade & eXecute
</code></pre>
<h2><a class="header" href="#window" id="window">window</a></h2>
<pre><code class="language-markdown"> key fn description
----------------------------------------------
C-x 0 delete-window kill focused window
C-x 1 delete-other-windows kill all other windows
C-x 2 split-window-below split horizontal
C-x 3 split-window-right split vertical
C-x o other-window other window (cycle)
</code></pre>
<h2><a class="header" href="#buffer" id="buffer">buffer</a></h2>
<pre><code class="language-markdown"> key fn description
---------------------------------------------
C-x C-q read-only-mode toggle read-only mode for buffer
C-x k kill-buffer kill buffer
C-x s save-some-buffers save buffer
C-x w write-file write buffer (save as)
C-x b switch-to-buffer switch buffer
C-x C-b list-buffers buffer list
</code></pre>
<h2><a class="header" href="#ibuffer" id="ibuffer">ibuffer</a></h2>
<p>Builtin advanced buffer selection mode</p>
<pre><code class="language-markdown"> key fn description
--------------------------------------
ibuffer enter buffer selection
h ibuffer help
o open buffer in other window
C-o open buffer in other window keep focus in ibuffer
s a sort by buffer name
s f sort by file name
s v sort by last viewed
s v sort by major mode
, cycle sorting mode
= compare buffer against file on disk (if file is dirty `*`)
/m filter by major mode
/n filter by buffer name
/f filter by file name
// remove all filter
/g create filter group
/\ remove all filter groups
</code></pre>
<h2><a class="header" href="#isearch" id="isearch">isearch</a></h2>
<pre><code class="language-markdown"> key fn description
-------------------------------------------------
C-s isearch-forward search forward from current position (C-s to go to next match)
C-r isearch-backward search backwards from current position (C-r to go to next match)
C-w isearch-yank-word-or-char feed next word to current search (extend)
M-p isearch-ring-advance previous search input
M-n isearch-ring-retreat next search input
</code></pre>
<h2><a class="header" href="#occur" id="occur">occur</a></h2>
<pre><code class="language-markdown"> key fn description
-----------------------------------
M-s o occur get matches for regexp in buffer
use during `isearch` to use current search term
C-n goto next line
C-p goto previous line
o open match in other window
C-o open match in other window keep focus in ibuffer
</code></pre>
<pre><code class="language-markdown"> key fn description
---------------------------------------------------------
multi-occur-in-matching-buffers run occur in buffers matching regexp
</code></pre>
<h2><a class="header" href="#grep" id="grep">grep</a></h2>
<pre><code class="language-markdown"> key fn description
-----------------------------------
rgrep recursive grep
find-grep run find-grep result in *grep* buffer
n/p navigate next/previous match in *grep* buffer
q quit *grep* buffer
</code></pre>
<h2><a class="header" href="#yankpaste" id="yankpaste">yank/paste</a></h2>
<pre><code class="language-markdown"> key fn description
---------------------------------------------
C-<SPACE> set-mark-command set start mark to select text
M-w kill-ring-save copy selected text
C-w kill-region kill selected text
C-y yank paste selected text
M-y yank-pop cycle through kill-ring (only after paste)
</code></pre>
<h2><a class="header" href="#register" id="register">register</a></h2>
<pre><code class="language-markdown"> key fn description
------------------------------------------------
C-x r s <reg> copy-to-register save region in register <reg>
C-x r i <reg> insert-register insert content of register <reg>
</code></pre>
<h2><a class="header" href="#blockrect" id="blockrect">block/rect</a></h2>
<pre><code class="language-markdown"> key fn description
------------------------------------------------
C-x <SPC> rectangle-mark-mode activate rectangle-mark-mode
string-rectangle insert text in marked rect
</code></pre>
<h2><a class="header" href="#mass-edit" id="mass-edit">mass edit</a></h2>
<pre><code class="language-markdown"> key fn description
------------------------------------------------
C-x h mark-whole-buffer mark whole buffer
delete-matching-line delete lines matching regex
M-% query-replace search & replace
C-M-% query-replace-regexp search & replace regex
</code></pre>
<h2><a class="header" href="#narrow" id="narrow">narrow</a></h2>
<pre><code class="language-markdown"> key fn description
---------------------------------------------
C-x n n narrow-to-region show only focused region (narrow)
C-x n w widen show whole buffer (wide)
</code></pre>
<h2><a class="header" href="#org" id="org">org</a></h2>
<pre><code class="language-markdown"> key fn description
------------------------------------
M-up/M-down re-arrange items in same hierarchy
M-left/M-right change item hierarchy
C-RET create new item below current
C-S-RET create new TODO item below current
S-left/S-right cycle TODO states
</code></pre>
<h3><a class="header" href="#org-source" id="org-source">org source</a></h3>
<pre><code class="language-markdown"> key fn description
------------------------------
<s TAB generate a source block
C-c ' edit source block (in lang specific buffer)
C-c C-c eval source block
</code></pre>
<h2><a class="header" href="#comapny" id="comapny">comapny</a></h2>
<pre><code class="language-markdown"> key fn description
-------------------------------
C-s search through completion candidates
C-o filter completion candidates based on search term
<f1> get doc for completion condidate
M-<digit> select completion candidate
</code></pre>
<h2><a class="header" href="#tags-1" id="tags-1">tags</a></h2>
<p>To generate <code>etags</code> using <code>ctags</code></p>
<pre><code class="language-markdown"> ctags -R -e . generate emacs tag file (important `-e`)
</code></pre>
<p>Navigate using tags</p>
<pre><code class="language-markdown"> key fn description
-----------------------------------------------
xref-find-definitions find definition of tag
xref-find-apropos find symbols matching regexp
xref-find-references find references of tag
</code></pre>
<h2><a class="header" href="#lisp" id="lisp">lisp</a></h2>
<pre><code class="language-markdown"> key fn description
------------------------------
ielm open interactive elips shell
</code></pre>
<p>In <code>lisp-interaction-mode</code> (<code>*scratch*</code> buffer by defult)</p>
<pre><code class="language-markdown"> key fn description
--------------------------------------------------------
C-j eval-print-last-sexp evaluate & print preceeding lisp expr
C-x C-e eval-last-sexp evaluate lisp expr
C-u C-x C-e eval-last-sexp evaluate & print
</code></pre>
<h2><a class="header" href="#ido" id="ido">ido</a></h2>
<p>Builtin fuzzy completion mode (eg buffer select, dired, ...).</p>
<pre><code class="language-markdown"> key fn description
------------------------------------------
ido-mode toggle ido mode
<Left>/<Right> cycle through available competions
<RET> select completion
</code></pre>
<h2><a class="header" href="#evil" id="evil">evil</a></h2>
<pre><code class="language-markdown"> key fn description
--------------------------
C-z toggle emacs/evil mode
C-^ toggle between previous and current buffer
C-p after paste cycle kill-ring back
C-n after paste cycle kill-ring forward
</code></pre>
<h2><a class="header" href="#dired" id="dired">dired</a></h2>
<pre><code class="language-markdown"> key fn description
--------------------------
i open sub-dir in same buffer
+ create new directory
C copy file/dir
q quit
</code></pre>
<h1><a class="header" href="#gpg1" id="gpg1">gpg(1)</a></h1>
<pre><code>gpg
-o|--output Specify output file
-a|--armor Create ascii output
-u|--local-user <name> Specify key for signing
-r|--recipient Encrypt for user
</code></pre>
<h2><a class="header" href="#generate-new-keypair" id="generate-new-keypair">Generate new keypair</a></h2>
<pre><code class="language-bash">gpg --full-generate-key
</code></pre>
<h2><a class="header" href="#list-keys" id="list-keys">List keys</a></h2>
<pre><code>gpg -k / --list-key # public keys
gpg -K / --list-secret-keys # secret keys
</code></pre>
<h2><a class="header" href="#edit-keys" id="edit-keys">Edit keys</a></h2>
<pre><code class="language-bash">gpg --edit-key <KEY ID>
</code></pre>
<p>Gives prompt to modify <code>KEY ID</code>, common commands:</p>
<pre><code class="language-bash">help show help
save save & quit
list list keys and user IDs
key <N> select subkey <N>
uid <N> select user ID <N>
expire change expiration of selected key
adduid add user ID
deluid delete selected user ID
addkey add subkey
delkey delete selected subkey
</code></pre>
<h2><a class="header" href="#export--import-keys" id="export--import-keys">Export & Import Keys</a></h2>
<pre><code class="language-bash">gpg --export --armor --output <KEY.PUB> <KEY ID>
gpg --import <FILE>
</code></pre>
<h2><a class="header" href="#search--send-keys" id="search--send-keys">Search & Send keys</a></h2>
<pre><code class="language-bash">gpg --keyserver <SERVER> --send-keys <KEY ID>
gpg --keyserver <SERVER> --search-keys <KEY ID>
</code></pre>
<h2><a class="header" href="#encrypt-passphrase" id="encrypt-passphrase">Encrypt (passphrase)</a></h2>
<p>Encrypt file using <code>passphrase</code> and write encrypted data to <code><file>.gpg</code>.</p>
<pre><code class="language-bash">gpg --symmetric <file>
# Decrypt using passphrase
gpg -o <file> --decrypt <file>.gpg
</code></pre>
<h2><a class="header" href="#encrypt-public-key" id="encrypt-public-key">Encrypt (public key)</a></h2>
<p>Encrypt file with <code>public key</code> of specified <code>recipient</code> and write encrypted
data to <code><file>.gpg</code>.</p>
<pre><code class="language-bash">gpg --encrypt -r foo@bar.de <file>
# Decrypt at foos side (private key required)
gpg -o <file> --decrypt <file>.gpg
</code></pre>
<h2><a class="header" href="#signing" id="signing">Signing</a></h2>
<p>Generate a signed file and write to <code><file>.gpg</code>.</p>
<pre><code class="language-bash">gpg --sign -u foor@bar.de <file>
# Verify
gpg --verify <file>
# Extract content from signed file
gpg -o <file> --decrypt <file>.gpg
</code></pre>
<blockquote>
<p>Without <code>-u</code> use first private key in list <code>gpg -K</code> for signing.</p>
</blockquote>
<p>Files can also be <code>signed</code> and <code>encrypted</code> at once, gpg will first sign the
file and then encrypt it.</p>
<pre><code class="language-bash">gpg --sign --encrypt <file>
</code></pre>
<h2><a class="header" href="#signing-detached" id="signing-detached">Signing (detached)</a></h2>
<p>Generate a <code>detached</code> signature and write to <code><file>.asc</code>.
Send <code><file>.asc</code> along with <code><file></code> when distributing.</p>
<pre><code class="language-bash">gpg --detach-sign --armor -u foor@bar.de <file>
# Verify
gpg --verify <file>.asc <file>
</code></pre>
<blockquote>
<p>Without <code>-u</code> use first private key in list <code>gpg -K</code> for signing.</p>
</blockquote>
<h2><a class="header" href="#abbreviations" id="abbreviations">Abbreviations</a></h2>
<ul>
<li><code>sec</code> secret key</li>
<li><code>ssb</code> secret subkey</li>
<li><code>pub</code> public key</li>
<li><code>sub</code> public subkey</li>
</ul>
<h2><a class="header" href="#keyservers" id="keyservers">Keyservers</a></h2>
<ul>
<li>http://pgp.mit.edu</li>
<li>http://keyserver.ubuntu.com</li>
<li>hkps://pgp.mailbox.org</li>
</ul>
<h1><a class="header" href="#gdb1" id="gdb1">gdb(1)</a></h1>
<h1><a class="header" href="#cli" id="cli">CLI</a></h1>
<pre><code class="language-markdown"> gdb [opts] [prg [-c coredump | -p pid]]
gdb [opts] --args prg <prg-args>
opts:
-p <pid> attach to pid
-c <coredump> use <coredump>
-x <file> execute script <file> before prompt
-ex <cmd> execute command <cmd> before prompt
--tty <tty> set I/O tty for debugee
</code></pre>
<h1><a class="header" href="#interactive-usage" id="interactive-usage">Interactive usage</a></h1>
<h2><a class="header" href="#misc" id="misc">Misc</a></h2>
<pre><code class="language-markdown"> tty <tty>
Set <tty> as tty for debugee.
Make sure nobody reads from target tty, easiest is to spawn a shell
and run following in target tty:
> while true; do sleep 1024; done
sharedlibrary [<regex>]
Load symbols of shared libs loaded by debugee. Optionally use <regex>
to filter libs for symbol loading.
display [/FMT] <expr>
Print <expr> every time debugee stops. Eg print next instr, see
examples below.
undisplay [<num>]
Delete display expressions either all or one referenced by <num>.
info display
List display expressions.
</code></pre>
<h2><a class="header" href="#breakpoints" id="breakpoints">Breakpoints</a></h2>
<pre><code class="language-markdown"> break [-qualified] <sym> thread <tnum>
Set a breakpoint only for a specific thread.
-qualified: Treat <sym> as fully qualified symbol (quiet handy to set
breakpoints on C symbols in C++ contexts)
break <sym> if <cond>
Set conditional breakpoint (see examples below).
delete [<num>]
Delete breakpoint either all or one referenced by <num>.
info break
List breakpoints.
cond <bp> <cond>
Make existing breakpoint <bp> conditional with <cond>.
tbreak
Set temporary breakpoint, will be deleted when hit.
Same syntax as `break`.
rbreak <regex>
Set breakpoints matching <regex>, where matching internally is done
on: .*<regex>.*
command [<bp_list>]
Define commands to run after breakpoint hit. If <bp_list> is not
specified attach command to last created breakpoint. Command block
terminated with 'end' token.
<bp_list>: Space separates list, eg 'command 2 5-8' to run command
for breakpoints: 2,5,6,7,8.
</code></pre>
<h2><a class="header" href="#inspection-1" id="inspection-1">Inspection</a></h2>
<pre><code class="language-markdown"> info functions [<regex>]
List functions matching <regex>. List all functions if no <regex>
provided.
info variables [<regex>]
List variables matching <regex>. List all variables if no <regex>
provided.
</code></pre>
<h2><a class="header" href="#signal-handling" id="signal-handling">Signal handling</a></h2>
<pre><code class="language-markdown"> info handle [<signal>]
Print how to handle <signal>. If no <signal> specified print for all
signals.
handle <signal> <action>
Configure how gdb handles <signal> sent to debugee.
<action>:
stop/nostop Catch signal in gdb and break.
print/noprint Print message when gdb catches signal.
pass/nopass Pass signal down to debugee.
catch signal <signal>
Create a catchpoint for <signal>.
</code></pre>
<h2><a class="header" href="#source-file-locations" id="source-file-locations">Source file locations</a></h2>
<pre><code class="language-markdown"> dir <path>
Add <path> to the beginning of the searh path for source files.
show dir
Show current search path.
set substitute-path <from> <to>
Add substitution rule checked during source file lookup.
show substitute-path
Show current substitution rules.
</code></pre>
<h2><a class="header" href="#configuration" id="configuration">Configuration</a></h2>
<pre><code class="language-markdown"> set follow-fork-mode <child | parent>
Specify which process to follow when debuggee makes a fork(2)
syscall.
set pagination <on | off>
Turn on/off gdb's pagination.
set breakpoint pending <on | off | auto>
on: always set pending breakpoints.
off: error when trying to set pending breakpoints.
auto: interatively query user to set breakpoint.
set print pretty <on | off>
Turn on/off pertty printing of structures.
set logging <on | off>
Enable output logging to file (default gdb.txt).
set logging file <fname>
Change output log file to <fname>
set logging redirect <on/off>
on: only log to file.
off: log to file and tty.
</code></pre>
<h1><a class="header" href="#user-commands-macros" id="user-commands-macros">User commands (macros)</a></h1>
<p>Gdb allows to create & document user commands as follows:</p>
<pre><code class="language-markdown"> define <cmd>
# cmds
end
document <cmd>
# docu
end
</code></pre>
<p>To get all user commands or documentations one can use:</p>
<pre><code class="language-markdown"> help user-defined
help <cmd>
</code></pre>
<h1><a class="header" href="#hooks" id="hooks">Hooks</a></h1>
<p>Gdb allows to create two types of command <code>hooks</code></p>
<ul>
<li><code>hook-</code> will be run before <code><cmd></code></li>
<li><code>hookpost-</code> will be run after <code><cmd></code></li>
</ul>
<pre><code class="language-markdown"> define hook-<cmd>
# cmds
end
define hookpost-<cmd>
# cmds
end
</code></pre>
<h1><a class="header" href="#examples-1" id="examples-1">Examples</a></h1>
<h2><a class="header" href="#automatically-print-next-instr" id="automatically-print-next-instr">Automatically print next instr</a></h2>
<p>When ever the debugee stops automatically print the memory at the current
instruction pointer (<code>$rip</code> x86) and format as instruction <code>/i</code>.</p>
<pre><code class="language-markdown"> # rip - x86
display /i $rip
# step instruction, after the step the next instruction is automatically printed
si
</code></pre>
<h2><a class="header" href="#conditional-breakpoints" id="conditional-breakpoints">Conditional breakpoints</a></h2>
<p>Create conditional breakpoints for a function <code>void foo(int i)</code> in the debugee.</p>
<pre><code class="language-markdown"> # Create conditional breakpoint
b foo if i == 42
b foo # would create bp 2
# Make existing breakpoint conditional
cond 2 if i == 7
</code></pre>
<h2><a class="header" href="#catch-sigsegv-and-execute-commands" id="catch-sigsegv-and-execute-commands">Catch SIGSEGV and execute commands</a></h2>
<p>This creates a <code>catchpoint</code> for the <code>SIGSEGV</code> signal and attached the <code>command</code>
to it.</p>
<pre><code class="language-markdown"> catch signal SIGSEGV
command
bt
c
end
</code></pre>
<h2><a class="header" href="#run-backtrace-on-thread-1-batch-mode" id="run-backtrace-on-thread-1-batch-mode">Run <code>backtrace</code> on thread 1 (batch mode)</a></h2>
<pre><code class="language-markdown"> gdb --batch -ex 'thread 1' -ex 'bt' -p <pid>
</code></pre>
<h2><a class="header" href="#script-gdb-for-automating-debugging-sessions" id="script-gdb-for-automating-debugging-sessions">Script gdb for automating debugging sessions</a></h2>
<p>To script gdb add commands into a file and pass it to gdb via <code>-x</code>.
For example create <code>run.gdb</code>:</p>
<pre><code class="language-markdown"> set pagination off
break mmap
command
info reg rdi rsi rdx
bt
c
end
#initial drop
c
</code></pre>
<p>This script can be used as:</p>
<pre><code class="language-markdown"> gdb --batch -x ./run.gdb -p <pid>
</code></pre>
<h1><a class="header" href="#know-bugs" id="know-bugs">Know Bugs</a></h1>
<h2><a class="header" href="#workaround-command--finish-bug" id="workaround-command--finish-bug">Workaround <code>command + finish</code> bug</a></h2>
<p>When using <code>finish</code> inside a <code>command</code> block, commands after <code>finish</code> are not
executed. To workaround that bug one can create a wrapper function which calls
<code>finish</code>.</p>
<pre><code class="language-markdown"> define handler
bt
finish
info reg rax
end
command
handler
end
</code></pre>
<h1><a class="header" href="#radare21" id="radare21">radare2(1)</a></h1>
<h2><a class="header" href="#print" id="print">print</a></h2>
<pre><code class="language-markdown">
pd <n> [@ <addr>] # print disassembly for <n> instructions
# with optional temporary seek to <addr>
</code></pre>
<h2><a class="header" href="#flags" id="flags">flags</a></h2>
<pre><code class="language-markdown"> fs # list flag-spaces
fs <fs> # select flag-space <fs>
f # print flags of selected flag-space
</code></pre>
<h2><a class="header" href="#help-1" id="help-1">help</a></h2>
<pre><code class="language-markdown"> ?*~<kw> # '?*' list all commands and '~' grep for <kw>
?*~... # '..' less mode /'...' interactive search
</code></pre>
<h2><a class="header" href="#relocation" id="relocation">relocation</a></h2>
<pre><code class="language-markdown"> > r2 -B <baddr> <exe> # open <exe> mapped to addr <baddr>
oob <addr> # reopen current file at <baddr>
</code></pre>
<h1><a class="header" href="#qemu1" id="qemu1">qemu(1)</a></h1>
<p>All the examples & notes use <code>qemu-system-x86_64</code> but in most cases
this can be swapped with the system emulator for other architectures.</p>
<h2><a class="header" href="#keybindings-1" id="keybindings-1">Keybindings</a></h2>
<pre><code class="language-markdown">Ctrl+Alt+g release mouse capture from VM
Ctrl+Alt+1 switch to display of VM
Ctrl+Alt+2 switch to qemu monitor
</code></pre>
<h2><a class="header" href="#vm-config-snippet" id="vm-config-snippet">VM config snippet</a></h2>
<p>Following command-line gives a good starting point to assemble a VM:</p>
<pre><code class="language-bash">qemu-system-x86_64 \
-cpu host -enable-kvm -smp 4 \
-m 8G \
-vga virtio -display sdl,gl=on \
-boot menu=on \
-cdrom <iso> \
-hda <disk> \
-device qemu-xhci,id=xhci \
-device usb-host,bus=xhci.0,vendorid=0x05e1,productid=0x0408,id=capture-card
</code></pre>
<h3><a class="header" href="#cpu--ram" id="cpu--ram">CPU & RAM</a></h3>
<ul>
<li><code>-cpu host</code> emulate host CPU in guest VM</li>
<li><code>-enable-kvm</code> use KVM instead software models (requires KVM on host machine)</li>
<li><code>-smp <N></code> number of guest CPUs</li>
</ul>
<blockquote>
<p>List available CPUs <code>qemu-system-x86_64 -cpu help</code>.</p>
</blockquote>
<ul>
<li><code>-m 8G</code> size of guest RAM</li>
</ul>
<h3><a class="header" href="#graphic--display" id="graphic--display">Graphic & Display</a></h3>
<ul>
<li><code>-vga virtio</code> use virtio as 3D video graphic accelerator (requires virgl in guest)</li>
<li><code>-display sdl,gl=on</code> use sdl window and enable openGL context</li>
</ul>
<h3><a class="header" href="#boot-menu" id="boot-menu">Boot Menu</a></h3>
<ul>
<li><code>-boot menu=on</code> enables boot menu to select boot device (enter with <code>ESC</code>)</li>
</ul>
<h3><a class="header" href="#block-devices" id="block-devices">Block devices</a></h3>
<ul>
<li><code>-cdrom <iso></code> attach cdrom drive with iso to a VM</li>
<li><code>-hda <disk></code> attach disk drive to a VM</li>
<li><code>-drive file=<file>,format=qcow2</code> generic way to configure & attach a drive to a VM</li>
</ul>
<h4><a class="header" href="#create-a-disk-with-a-hrefhttpsqemureadthedocsioenlatesttoolsqemu-imghtmlqemu-imga" id="create-a-disk-with-a-hrefhttpsqemureadthedocsioenlatesttoolsqemu-imghtmlqemu-imga">Create a disk with <a href="https://qemu.readthedocs.io/en/latest/tools/qemu-img.html"><code>qemu-img</code></a></a></h4>
<p>To create a <code>qcow2</code> disk (qemu copy-on-write) of size <code>10G</code>:</p>
<pre><code class="language-bash">qemu-img create -f qcow2 disk.qcow2 10G
</code></pre>
<p>The disk does not contain any <code>partitions</code> or a <code>partition table</code>.
We can format the disk from <strong>within the <strong>guest</strong></strong> as following example:</p>
<pre><code class="language-bash"># Create `gpt` partition table.
sudo parted /dev/sda mktable gpt
# Create two equally sized primary partitions.
sudo parted /dev/sda mkpart primary 0% 50%
sudo parted /dev/sda mkpart primary 50% 100%
# Create filesystem on each partition.
sudo mkfs.ext3 /dev/sda1
sudo mkfs.ext4 /dev/sda2
lsblk -f /dev/sda
NAME FSTYPE LABEL UUID FSAVAIL FSUSE% MOUNTPOINT
sda
├─sda1 ext3 ....
└─sda2 ext4 ....
</code></pre>
<h3><a class="header" href="#usb" id="usb">USB</a></h3>
<h4><a class="header" href="#host-controller" id="host-controller">Host Controller</a></h4>
<ul>
<li><code>-device qemu-xhci,id=xhci</code> add XHCI USB controller to the VM (supports USB 3.0, 2.0, 1.1). <code>id=xhci</code> creates a usb bus named <code>xhci</code>.</li>
</ul>
<h4><a class="header" href="#usb-device" id="usb-device">USB Device</a></h4>
<ul>
<li><code>-device usb-host,bus=xhci.0,vendorid=0x05e1,productid=0x0408</code> pass-through USB device from host identified by vendorid & productid and attach to usb bus <code>xhci.0</code> (defined with controller <code>id</code>)</li>
</ul>
<h2><a class="header" href="#references" id="references">References</a></h2>
<ul>
<li><a href="https://github.com/qemu/qemu/blob/master/docs/usb2.txt">QEMU USB</a></li>
<li><a href="https://qemu.readthedocs.io/en/latest/tools/qemu-img.html">QEMU IMG</a></li>
<li><a href="https://qemu.readthedocs.io/en/latest/tools/index.html">QEMU Tools</a></li>
<li><a href="https://www.qemu.org/docs/master/system/index.html">QEMU System</a></li>
</ul>
<h1><a class="header" href="#resource-analysis--monitor" id="resource-analysis--monitor">Resource analysis & monitor</a></h1>
<ul>
<li><a href="monitor/./lsof.html">lsof</a></li>
<li><a href="monitor/./ss.html">ss</a></li>
<li><a href="monitor/./pidstat.html">pidstat</a></li>
<li><a href="monitor/./pgrep.html">pgrep</a></li>
<li><a href="monitor/./pmap.html">pmap</a></li>
<li><a href="monitor/./pstack.html">pstack</a></li>
</ul>
<h1><a class="header" href="#lsof8" id="lsof8">lsof(8)</a></h1>
<pre><code class="language-markdown">lsof
-r <s> ..... repeatedly execute command ervery <s> seconds
-a ......... AND slection filters instead ORing (OR: default)
-p <pid> ... filter by <pid>
+fg ........ show file flags for file descripros
-n ......... don't convert network addr to hostnames
-P ......... don't convert network port to service names
-i <@h[:p]>. show connections to h (hostname|ip addr) with optional port p
-s <p:s> ... in conjunction with '-i' filter for protocol <p> in state <s>
-U ......... show unix domain sockets ('@' indicates abstract sock name, see unix(7))
</code></pre>
<pre><code class="language-markdown">file flags:
R/W/RW ..... read/write/read-write
CR ......... create
AP ......... append
TR ......... truncate
</code></pre>
<pre><code class="language-markdown">-s protocols
TCP, UDP
-s states (TCP)
CLOSED, IDLE, BOUND, LISTEN, ESTABLISHED, SYN_SENT, SYN_RCDV, ESTABLISHED,
CLOSE_WAIT, FIN_WAIT1, CLOSING, LAST_ACK, FIN_WAIT_2, TIME_WAIT
-s states (UDP)
Unbound, Idle
</code></pre>
<h1><a class="header" href="#examples-2" id="examples-2">Examples</a></h1>
<h2><a class="header" href="#file-flags" id="file-flags">File flags</a></h2>
<p>Show open files with file flags for process:</p>
<pre><code class="language-markdown">lsof +fg -p <pid>
</code></pre>
<h2><a class="header" href="#open-tcp-connections" id="open-tcp-connections">Open TCP connections</a></h2>
<p>Show open tcp connections for <code>$USER</code>:</p>
<pre><code class="language-markdown">lsof -a -u $USER -i TCP
</code></pre>
<p><strong>Note</strong>: <code>-a</code> <em>ands</em> the results. If <code>-a</code> is not given all open files matching
<code>$USER</code> and all tcp connections are listed (<em>ored</em>).</p>
<h2><a class="header" href="#open-connection-to-specific-host" id="open-connection-to-specific-host">Open connection to specific host</a></h2>
<p>Show open connections to <code>localhost</code> for <code>$USER</code>:</p>
<pre><code class="language-markdown">lsof -a -u $USER -i @localhost
</code></pre>
<h2><a class="header" href="#open-connection-to-specific-port" id="open-connection-to-specific-port">Open connection to specific port</a></h2>
<p>Show open connections to port <code>:1234</code> for <code>$USER</code>:</p>
<pre><code class="language-markdown">lsof -a -u $USER -i :1234
</code></pre>
<h2><a class="header" href="#ipv4-tcp-connections-in-established-state" id="ipv4-tcp-connections-in-established-state">IPv4 TCP connections in <code>ESTABLISHED</code> state</a></h2>
<pre><code class="language-markdown">lsof -i 4TCP -s TCP:ESTABLISHED
</code></pre>
<h1><a class="header" href="#ss8" id="ss8">ss(8)</a></h1>
<pre><code class="language-markdown">ss [option] [filter]
</code></pre>
<pre><code class="language-markdown">[option]
-p ..... Show process using socket
-l ..... Show sockets in listening state
-4/-6 .. Show IPv4/6 sockets
-x ..... Show unix sockets
-n ..... Show numeric ports (no resolve)
-O ..... Oneline output per socket
</code></pre>
<pre><code class="language-markdown">[filter]
dport/sport PORT .... Filter for destination/source port
dst/src ADDR ........ Filter for destination/source address
and/or .............. Logic operator
==/!= ............... Comparison operator
(EXPR) .............. Group exprs
</code></pre>
<h1><a class="header" href="#examples-3" id="examples-3">Examples</a></h1>
<p>Show all tcp IPv4 sockets connecting to port <code>443</code>:</p>
<pre><code class="language-markdown">ss -4 'dport 443'
</code></pre>
<p>Show all tcp IPv4 sockets that don't connect to port <code>443</code> or connect to address <code>1.2.3.4</code>.</p>
<pre><code class="language-markdown">ss -4 'dport != 443 or dst 1.2.3.4'
</code></pre>
<h1><a class="header" href="#pidstat1" id="pidstat1">pidstat(1)</a></h1>
<pre><code class="language-markdown">pidstat [opt] [interval] [cont]
-U [user] show username instead UID, optionally only show for user
-r memory statistics
-d I/O statistics
-h single line per process and no lines with average
</code></pre>
<h1><a class="header" href="#page-fault-and-memory-utilization" id="page-fault-and-memory-utilization">Page fault and memory utilization</a></h1>
<pre><code class="language-markdown">pidstat -r -p <pid> [interval] [count]
</code></pre>
<pre><code class="language-markdown">minor_pagefault: Happens when the page needed is already in memory but not
allocated to the faulting process, in that case the kernel
only has to create a new page-table entry pointing to the
shared physical page (not required to load a memory page from
disk).
major_pagefault: Happens when the page needed is NOT in memory, the kernel
has to create a new page-table entry and populate the
physical page (required to load a memory page from disk).
</code></pre>
<h1><a class="header" href="#io-statistics" id="io-statistics">I/O statistics</a></h1>
<pre><code class="language-markdown">pidstat -d -p <pid> [interval] [count]
</code></pre>
<h1><a class="header" href="#pgrep1" id="pgrep1">pgrep(1)</a></h1>
<pre><code class="language-markdown">pgrep [opts] <pattern>
-n only list newest matching process
-u <usr> only show matching for user <usr>
-l additionally list command
-a additionally list command + arguments
</code></pre>
<h2><a class="header" href="#debug-newest-process" id="debug-newest-process">Debug newest process</a></h2>
<p>For example attach gdb to newest zsh process from <code>$USER</code>.</p>
<pre><code class="language-markdown">gdb -p $(pgrep -n -u $USER zsh)
</code></pre>
<h1><a class="header" href="#pmap1" id="pmap1">pmap(1)</a></h1>
<pre><code class="language-markdown">pmap <pid>
Dump virtual memory map of process.
Compared to /proc/<pid>/maps it shows the size of the mappings.
</code></pre>
<h1><a class="header" href="#pstack1" id="pstack1">pstack(1)</a></h1>
<pre><code class="language-markdown">pstack <pid>
Dump stack for all threads of process.
</code></pre>
<h1><a class="header" href="#trace-and-profile" id="trace-and-profile">Trace and Profile</a></h1>
<ul>
<li><a href="trace_profile/./strace.html">strace</a></li>
<li><a href="trace_profile/./ltrace.html">ltrace</a></li>
<li><a href="trace_profile/./perf.html">perf</a></li>
<li><a href="trace_profile/./oprofile.html">OProfile</a></li>
<li><a href="trace_profile/./time.html">time</a></li>
</ul>
<h1><a class="header" href="#strace1" id="strace1">strace(1)</a></h1>
<pre><code class="language-markdown">strace [opts] [prg]
-f .......... follow child processes on fork(2)
-p <pid> .... attach to running process
-s <size> ... max string size, truncate of longer (default: 32)
-e <expr> ... expression for trace filtering
-o <file> ... log output into <file>
-c .......... dump syscall statitics at the end
</code></pre>
<pre><code class="language-markdown"><expr>:
trace=syscall[,syscall] .... trace only syscall listed
trace=file ................. trace all syscall that take a filename as arg
trace=process .............. trace process management related syscalls
trace=signal ............... trace signal related syscalls
signal ..................... trace signals delivered to the process
</code></pre>
<h1><a class="header" href="#examples-4" id="examples-4">Examples</a></h1>
<p>Trace <code>open(2)</code> & <code>socket(2)</code> syscalls for a running process + child processes:</p>
<pre><code class="language-markdown">strace -f -e trace=open,socket -p <pid>
</code></pre>
<p>Trace signals delivered to a running process:</p>
<pre><code class="language-markdown">strace -f -e signal -p <pid>
</code></pre>
<h1><a class="header" href="#ltrace1" id="ltrace1">ltrace(1)</a></h1>
<pre><code class="language-markdown">ltrace [opts] [prg]
-f .......... follow child processes on fork(2)
-p <pid> .... attach to running process
-o <file> ... log output into <file>
-l <filter> . show who calls into lib matched by <filter>
-C .......... demangle
</code></pre>
<h1><a class="header" href="#example-4" id="example-4">Example</a></h1>
<p>List which program/libs call into <code>libstdc++</code>:</p>
<pre><code class="language-bash">ltrace -l '*libstdc++*' -C -o ltrace.log ./main
</code></pre>
<h1><a class="header" href="#perf1" id="perf1">perf(1)</a></h1>
<pre><code class="language-markdown">perf list show supported hw/sw events
perf stat
-p <pid> .. show stats for running process
-I <ms> ... show stats periodically over interval <ms>
-e <ev> ... filter for events
perf top
-p <pid> .. show stats for running process
-F <hz> ... sampling frequency
-K ........ hide kernel threads
perf record
-p <pid> ............... record stats for running process
-F <hz> ................ sampling frequency
--call-graph <method> .. [fp, dwarf, lbr] method how to caputre backtrace
fp : use frame-pointer, need to compile with
-fno-omit-frame-pointer
dwarf: use .cfi debug information
lbr : use hardware last branch record facility
-g ..................... short-hand for --call-graph fp
-e <ev> ................ filter for events
perf report
-n .................... annotate symbols with nr of samples
--stdio ............... report to stdio, if not presen tui mode
-g graph,0.5,caller ... show caller based call chains with value >0.5
</code></pre>
<pre><code class="language-markdown">Useful <ev>:
page-faults
minor-faults
major-faults
cpu-cycles`
task-clock
</code></pre>
<h2><a class="header" href="#a-hrefhttpsgithubcombrendangreggflamegraphflamegrapha" id="a-hrefhttpsgithubcombrendangreggflamegraphflamegrapha"><a href="https://github.com/brendangregg/FlameGraph"><code>Flamegraph</code></a></a></h2>
<h3><a class="header" href="#flamegraph-with-single-event-trace" id="flamegraph-with-single-event-trace">Flamegraph with single event trace</a></h3>
<pre><code class="language-markdown">perf record -g -e cpu-cycles -p <pid>
perf script | FlameGraph/stackcollapse-perf.pl | FlameGraph/flamegraph.pl > cycles-flamegraph.svg
</code></pre>
<h3><a class="header" href="#flamegraph-with-multiple-event-traces" id="flamegraph-with-multiple-event-traces">Flamegraph with multiple event traces</a></h3>
<pre><code class="language-markdown">perf record -g -e cpu-cycles,page-faults -p <pid>
perf script --per-event-dump
# fold & generate as above
</code></pre>
<h1><a class="header" href="#a-hrefhttpsoprofilesourceforgeiooprofilea" id="a-hrefhttpsoprofilesourceforgeiooprofilea"><a href="https://oprofile.sourceforge.io/">OProfile</a></a></h1>
<pre><code class="language-markdown">operf -g -p <pid>
-g ...... caputre call-graph information
opreport [opt] FILE
show time spent per binary image
-l ...... show time spent per symbol
-c ...... show callgraph information (see below)
-a ...... add column with time spent accumulated over child nodes
ophelp show supported hw/sw events
</code></pre>
<h1><a class="header" href="#usrbintime1" id="usrbintime1">/usr/bin/time(1)</a></h1>
<pre><code class="language-markdown"># statistics of process run
/usr/bin/time -v <cmd>
</code></pre>
<h1><a class="header" href="#binary" id="binary">Binary</a></h1>
<ul>
<li><a href="binary/./od.html">od</a></li>
<li><a href="binary/./xxd.html">xxd</a></li>
<li><a href="binary/./readelf.html">readelf</a></li>
<li><a href="binary/./objdump.html">objdump</a></li>
<li><a href="binary/./nm.html">nm</a></li>
</ul>
<h1><a class="header" href="#od1" id="od1">od(1)</a></h1>
<pre><code class="language-markdown"> od [opts] <file>
-An don't print addr info
-tx4 print hex in 4 byte chunks
-ta print as named character
-tc printable chars or backslash escape
-w4 print 4 bytes per line
-j <n> skip <n> bytes from <file> (hex if start with 0x)
-N <n> dump <n> bytes (hex of start with 0x)
</code></pre>
<h2><a class="header" href="#ascii-to-hex-string" id="ascii-to-hex-string">ASCII to hex string</a></h2>
<pre><code class="language-markdown"> echo -n AAAABBBB | od -An -w4 -tx4
>> 41414141
>> 42424242
echo -n '\x7fELF\n' | od -tx1 -ta -tc
>> 0000000 7f 45 4c 46 0a # tx1
>> del E L F nl # ta
>> 177 E L F \n # tc
</code></pre>
<h2><a class="header" href="#extract-parts-of-file" id="extract-parts-of-file">Extract parts of file</a></h2>
<p>For example <code>.rodata</code> section from an elf file. We can use <code>readelf</code> to get the
offset into the file where the <code>.rodata</code> section starts.</p>
<pre><code class="language-markdown"> readelf -W -S foo
>> Section Headers:
>> [Nr] Name Type Address Off Size ES Flg Lk Inf Al
>> ...
>> [15] .rodata PROGBITS 00000000004009c0 0009c0 000030 00 A 0 0 16
</code></pre>
<p>With the offset of <code>-j 0x0009c0</code> we can dump <code>-N 0x30</code> bytes from the beginning of
the <code>.rodata</code> section as follows:</p>
<pre><code class="language-markdown"> od -j 0x0009c0 -N 0x30 -tx4 -w4 foo
>> 0004700 00020001
>> 0004704 00000000
>> *
>> 0004740 00000001
>> 0004744 00000002
>> 0004750 00000003
>> 0004754 00000004
</code></pre>
<p><strong>Note</strong>: Numbers starting with <code>0x</code> will be interpreted as hex by <code>od</code>.</p>
<h1><a class="header" href="#xxd1" id="xxd1">xxd(1)</a></h1>
<pre><code class="language-markdown"> xxd [opts]
-p dump continuous hexdump
-r convert hexdump into binary ('revert')
-e dump as little endian mode
-i output as C array
</code></pre>
<h2><a class="header" href="#ascii-to-hex-stream" id="ascii-to-hex-stream">ASCII to hex stream</a></h2>
<pre><code class="language-markdown"> echo -n 'aabb' | xxd -p
>> 61616262
</code></pre>
<h2><a class="header" href="#hex-to-binary-stream" id="hex-to-binary-stream">Hex to binary stream</a></h2>
<pre><code class="language-markdown"> echo -n '61616262' | xxd -p -r
>> aabb
</code></pre>
<h2><a class="header" href="#ascii-to-binary" id="ascii-to-binary">ASCII to binary</a></h2>
<pre><code class="language-markdown"> echo -n '\x7fELF' | xxd -p | xxd -p -r | file -p -
>> ELF
</code></pre>
<h2><a class="header" href="#ascii-to-c-array-hex-encoded" id="ascii-to-c-array-hex-encoded">ASCII to <code>C</code> array (hex encoded)</a></h2>
<pre><code class="language-markdown"> xxd -i <(echo -n '\x7fELF')
>> unsigned char _proc_self_fd_11[] = {
>> 0x7f, 0x45, 0x4c, 0x46
>> };
>> unsigned int _proc_self_fd_11_len = 4;
</code></pre>
<h1><a class="header" href="#readelf1" id="readelf1">readelf(1)</a></h1>
<pre><code class="language-markdown"> readelf [opts] <elf>
-W|--wide wide output, dont break output at 80 chars
-h print ELF header
-S print section headers
-l print program headers + segment mapping
-d print .dynamic section (dynamic link information)
--syms print symbol tables (.symtab .dynsym)
--dyn-syms print dynamic symbol table (exported symbols for dynamic linker)
-r print relocation sections (.rel.*, .rela.*)
</code></pre>
<h1><a class="header" href="#objdump1" id="objdump1">objdump(1)</a></h1>
<pre><code class="language-markdown"> objdump [opts] <elf>
-M intel use intil syntax
-d disassemble text section
-D disassemble all sections
-S mix disassembly with source code
-C demangle
-j <section> display info for section
--[no-]show-raw-insn [dont] show object code next to disassembly
</code></pre>
<h2><a class="header" href="#disassemble-section" id="disassemble-section">Disassemble section</a></h2>
<p>For example <code>.plt</code> section:</p>
<pre><code class="language-markdown"> objdump -j .plt -d <elf>
</code></pre>
<h1><a class="header" href="#nm1" id="nm1">nm(1)</a></h1>
<pre><code class="language-markdown"> nm [opts] <elf>
-C demangle
-u undefined only
</code></pre>
<h1><a class="header" href="#development" id="development">Development</a></h1>
<ul>
<li><a href="development/./c++filt.html">c++filt</a></li>
<li><a href="development/./c++.html">c++</a></li>
<li><a href="development/./glibc.html">glibc</a></li>
<li><a href="development/./gcc.html">gcc</a></li>
<li>[make] (./make.md)</li>
<li><a href="development/./ld.so.html">ld.so</a></li>
</ul>
<h1><a class="header" href="#cfilt1" id="cfilt1">c++filt(1)</a></h1>
<h2><a class="header" href="#demangle-symbol" id="demangle-symbol">Demangle symbol</a></h2>
<pre><code class="language-markdown"> c++-filt <symbol_str>
</code></pre>
<h2><a class="header" href="#demangle-stream" id="demangle-stream">Demangle stream</a></h2>
<p>For example dynamic symbol table:</p>
<pre><code class="language-markdown"> readelf -W --dyn-syms <elf> | c++filt
</code></pre>
<h1><a class="header" href="#c" id="c">c++</a></h1>
<h2><a class="header" href="#type-deduction" id="type-deduction">Type deduction</a></h2>
<p>Force compile error to see what <code>auto</code> is deduced to.</p>
<pre><code class="language-cpp">auto foo = bar();
// force compile error
typename decltype(foo)::_;
</code></pre>
<h1><a class="header" href="#glibc" id="glibc">glibc</a></h1>
<h2><a class="header" href="#malloc-tracer-a-hrefhttpman7orglinuxman-pagesman3mtrace3htmlmtrace3a" id="malloc-tracer-a-hrefhttpman7orglinuxman-pagesman3mtrace3htmlmtrace3a">malloc tracer <a href="http://man7.org/linux/man-pages/man3/mtrace.3.html"><code>mtrace(3)</code></a></a></h2>
<p>Trace memory allocation and de-allocation to detect memory leaks.
Need to call <code>mtrace(3)</code> to install the tracing hooks.</p>
<p>If we can't modify the binary to call <code>mtrace</code> we can create a small shared
library and pre-load it.</p>
<pre><code class="language-c">// libmtrace.c
#include <mcheck.h>
__attribute__((constructor)) static void init_mtrace() { mtrace(); }
</code></pre>
<p>Compile as:</p>
<pre><code class="language-bash">gcc -shared -fPIC -o libmtrace.so libmtrace.c
</code></pre>
<p>To generate the trace file run:</p>
<pre><code class="language-bash">export MALLOC_TRACE=<file>
LD_PRELOAD=./libmtrace.so <binary>
</code></pre>
<p><strong>Note</strong>: If <code>MALLOC_TRACE</code> is not set <code>mtrace</code> won't install tracing hooks.</p>
<p>To get the results of the trace file:</p>
<pre><code class="language-bash">mtrace <binary> $MALLOC_TRACE
</code></pre>
<h2><a class="header" href="#malloc-check-a-hrefhttpman7orglinuxman-pagesman3mallopt3htmlmallopt3a" id="malloc-check-a-hrefhttpman7orglinuxman-pagesman3mallopt3htmlmallopt3a">malloc check <a href="http://man7.org/linux/man-pages/man3/mallopt.3.html"><code>mallopt(3)</code></a></a></h2>
<p>Configure action when glibc detects memory error.</p>
<pre><code class="language-bash">export MALLOC_CHECK_=<N>
</code></pre>
<p>Useful values:</p>
<pre><code class="language-markdown">1 print detailed error & continue
3 print detailed error + stack trace + memory mappings & abort
7 print simple error message + stack trace + memory mappings & abort
</code></pre>
<h1><a class="header" href="#gcc1" id="gcc1">gcc(1)</a></h1>
<h2><a class="header" href="#cli-1" id="cli-1">CLI</a></h2>
<h3><a class="header" href="#preprocessing" id="preprocessing">Preprocessing</a></h3>
<p>While debugging can be helpful to just pre-process files.</p>
<pre><code class="language-bash">gcc -E [-dM] ...
</code></pre>
<ul>
<li><code>-E</code> run only preprocessor</li>
<li><code>-dM</code> list only <code>#define</code> statements</li>
</ul>
<h2><a class="header" href="#a-hrefhttpsgccgnuorgonlinedocsgccother-builtinshtmlbuiltinsa" id="a-hrefhttpsgccgnuorgonlinedocsgccother-builtinshtmlbuiltinsa"><a href="https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html">Builtins</a></a></h2>
<h3><a class="header" href="#__builtin_expectexpr-cond" id="__builtin_expectexpr-cond"><code>__builtin_expect(expr, cond)</code></a></h3>
<p>Give the compiler a hint which branch is hot, so it can lay out the code
accordingly to reduce number of jump instructions.
See on <a href="https://godbolt.org/z/MbTHAP">compiler explorer</a>.</p>
<pre><code class="language-bash">echo "
extern void foo();
extern void bar();
void run0(int x) {
if (__builtin_expect(x,0)) { foo(); }
else { bar(); }
}
void run1(int x) {
if (__builtin_expect(x,1)) { foo(); }
else { bar(); }
}
" | gcc -O2 -S -masm=intel -o /dev/stdout -xc -
</code></pre>
<p>Will generate something similar to the following.</p>
<ul>
<li><code>run0</code>: <code>bar</code> is on the path without branch</li>
<li><code>run1</code>: <code>foo</code> is on the path without branch</li>
</ul>
<pre><code class="language-x86asm">run0:
test edi, edi
jne .L4
xor eax, eax
jmp bar
.L4:
xor eax, eax
jmp foo
run1:
test edi, edi
je .L6
xor eax, eax
jmp foo
.L6:
xor eax, eax
jmp bar
</code></pre>
<h2><a class="header" href="#abi-linux" id="abi-linux">ABI (Linux)</a></h2>
<ul>
<li>C ABI - <a href="https://www.uclibc.org/docs/psABI-x86_64.pdf">SystemV ABI</a></li>
<li>C++ ABI - <a href="https://itanium-cxx-abi.github.io/cxx-abi">C++ Itanium ABI</a></li>
</ul>
<h1><a class="header" href="#make1" id="make1">make(1)</a></h1>
<h2><a class="header" href="#anatomy-of-make-rules" id="anatomy-of-make-rules">Anatomy of <code>make</code> rules</a></h2>
<pre><code class="language-make">target .. : prerequisite ..
recipe
..
</code></pre>
<ul>
<li><code>target</code>: an output generated by the rule</li>
<li><code>prerequisite</code>: an input that is used to generate the target</li>
<li><code>recipe</code>: list of actions to generate the output from the input</li>
</ul>
<blockquote>
<p>Use <code>make -p</code> to print all rules and variables (implicitly + explicitly defined).</p>
</blockquote>
<h2><a class="header" href="#pattern-rules--automatic-variables" id="pattern-rules--automatic-variables">Pattern rules & Automatic variables</a></h2>
<h3><a class="header" href="#pattern-rules" id="pattern-rules">Pattern rules</a></h3>
<p>A pattern rule contains the <code>%</code> char (exactly one of them) and look like this example:</p>
<pre><code class="language-make">%.o : %.c
$(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@
</code></pre>
<p>The target matches files of the pattern <code>%.o</code>, where <code>%</code> matches any none-empty
substring and other character match just them self.</p>
<p>The substring matched by <code>%</code> is called the <code>stem</code>.</p>
<p><code>%</code> in the prerequisite stands for the matched <code>stem</code> in the target.</p>
<h3><a class="header" href="#automatic-variables" id="automatic-variables">Automatic variables</a></h3>
<p>As targets and prerequisites in pattern rules can't be spelled explicitly in
the recipe, make provides a set of automatic variables to work with:</p>
<ul>
<li><code>$@</code>: Name of the target that triggered the rule.</li>
<li><code>$<</code>: Name of the first prerequisite.</li>
<li><code>$^</code>: Names of all prerequisites (without duplicates).</li>
<li><code>$+</code>: Names of all prerequisites (with duplicates).</li>
<li><code>$*</code>: Stem of the pattern rule.</li>
</ul>
<pre><code class="language-make"># file: Makefile
all: foobar blabla
foo% bla%: aaa bbb bbb
@echo "@ = $@"
@echo "< = $<"
@echo "^ = $^"
@echo "+ = $+"
@echo "* = $*"
@echo "----"
aaa:
bbb:
</code></pre>
<p>Running above <code>Makefile</code> gives:</p>
<pre><code class="language-test">@ = foobar
< = aaa
^ = aaa bbb
+ = aaa bbb bbb
* = bar
----
@ = blabla
< = aaa
^ = aaa bbb
+ = aaa bbb bbb
* = bla
----
</code></pre>
<h2><a class="header" href="#useful-functions" id="useful-functions">Useful functions</a></h2>
<h3><a class="header" href="#substitution-references" id="substitution-references">Substitution references</a></h3>
<p>Substitute strings matching pattern in a list.</p>
<pre><code class="language-make">in := a.o l.a c.o
out := $(in:.o=.c)
# => out = a.c l.a c.c
</code></pre>
<h3><a class="header" href="#filter" id="filter"><code>filter</code></a></h3>
<p>Keep strings matching a pattern in a list.</p>
<pre><code class="language-make">in := a.a b.b c.c d.d
out := $(filter %.b %.c, $(in))
# => out = b.b c.c
</code></pre>
<h3><a class="header" href="#filter-out" id="filter-out"><code>filter-out</code></a></h3>
<p>Remove strings matching a pattern from a list.</p>
<pre><code class="language-make">in := a.a b.b c.c d.d
out := $(filter-out %.b %.c, $(in))
# => out = a.a d.d
</code></pre>
<h3><a class="header" href="#abspath" id="abspath"><code>abspath</code></a></h3>
<p>Resolve each file name as absolute path (don't resolve symlinks).</p>
<pre><code class="language-make">$(abspath fname1 fname2 ..)
### `realpath`
Resolve each file name as canonical path.
```make
$(realpath fname1 fname2 ..)
</code></pre>
<h1><a class="header" href="#ldso8" id="ldso8">ld.so(8)</a></h1>
<h2><a class="header" href="#environment-variables" id="environment-variables">Environment Variables</a></h2>
<pre><code class="language-console"> LD_PRELOAD=<l_so> colon separated list of libso's to be pre loaded
LD_DEBUG=<opts> comma separated list of debug options
=help list available options
=libs show library search path
=files processing of input files
=symbols show search path for symbol lookup
=bindings show against which definition a symbol is bound
</code></pre>
<h2><a class="header" href="#ld_preload-initialization-order-and-link-map" id="ld_preload-initialization-order-and-link-map">LD_PRELOAD: Initialization Order and Link Map</a></h2>
<p>Libraries specified in <code>LD_PRELOAD</code> are loaded from <code>left-to-right</code> but
initialized from <code>right-to-left</code>.</p>
<pre><code class="language-markdown"> > ldd ./main
>> libc.so.6 => /usr/lib/libc.so.6
> LD_PRELOAD=liba.so:libb.so ./main
-->
preloaded in this order
<--
initialized in this order
</code></pre>
<p>The preload order determines:</p>
<ul>
<li>the order libraries are inserted into the <code>link map</code></li>
<li>the initialization order for libraries</li>
</ul>
<p>For the example listed above the resulting <code>link map</code> will look like the
following:</p>
<pre><code class="language-makrdown"> +------+ +------+ +------+ +------+
| main | -> | liba | -> | libb | -> | libc |
+------+ +------+ +------+ +------+
</code></pre>
<p>This can be seen when running with <code>LD_DEBUG=files</code>:</p>
<pre><code class="language-makrdown"> > LD_DEBUG=files LD_PRELOAD=liba.so:libb.so ./main
# load order (-> determines link map)
>> file=liba.so [0]; generating link map
>> file=libb.so [0]; generating link map
>> file=libc.so.6 [0]; generating link map
# init order
>> calling init: /usr/lib/libc.so.6
>> calling init: <path>/libb.so
>> calling init: <path>/liba.so
>> initialize program: ./main
</code></pre>
<p>To verify the <code>link map</code> order we let <code>ld.so</code> resolve the <code>memcpy(3)</code> libc
symbol (used in <em>main</em>) dynamically, while enabling <code>LD_DEBUG=symbols,bindings</code>
to see the resolving in action.</p>
<pre><code class="language-makrdown"> > LD_DEBUG=symbols,bindings LD_PRELOAD=liba.so:libb.so ./main
>> symbol=memcpy; lookup in file=./main [0]
>> symbol=memcpy; lookup in file=<path>/liba.so [0]
>> symbol=memcpy; lookup in file=<path>/libb.so [0]
>> symbol=memcpy; lookup in file=/usr/lib/libc.so.6 [0]
>> binding file ./main [0] to /usr/lib/libc.so.6 [0]: normal symbol `memcpy' [GLIBC_2.14]
</code></pre>
<h2><a class="header" href="#dynamic-linking-x86_64" id="dynamic-linking-x86_64">Dynamic Linking (x86_64)</a></h2>
<p>Dynamic linking basically works via one indirect jump. It uses a combination of
function trampolines (<code>.plt</code> section) and a function pointer table (<code>.got.plt</code>
section).
On the first call the trampoline sets up some metadata and then jumps to the
<code>ld.so</code> runtime resolve function, which in turn patches the table with the
correct function pointer.</p>
<pre><code class="language-makrdown"> .plt ....... procedure linkage table, contains function trampolines, usually
located in code segment (rx permission)
.got.plt ... global offset table for .plt, holds the function pointer table
</code></pre>
<p>Using <code>radare2</code> we can analyze this in more detail:</p>
<pre><code class="language-makrdown"> [0x00401040]> pd 4 @ section..got.plt
;-- section..got.plt:
;-- .got.plt: ; [22] -rw- section size 32 named .got.plt
;-- _GLOBAL_OFFSET_TABLE_:
[0] 0x00404000 .qword 0x0000000000403e10 ; section..dynamic
[1] 0x00404008 .qword 0x0000000000000000
; CODE XREF from section..plt @ +0x6
[2] 0x00404010 .qword 0x0000000000000000
;-- reloc.puts:
; CODE XREF from sym.imp.puts @ 0x401030
[3] 0x00404018 .qword 0x0000000000401036 ; RELOC 64 puts
[0x00401040]> pd 6 @ section..plt
;-- section..plt:
;-- .plt: ; [12] -r-x section size 32 named .plt
┌─> 0x00401020 ff35e22f0000 push qword [0x00404008]
â•Ž 0x00401026 ff25e42f0000 jmp qword [0x00404010]
â•Ž 0x0040102c 0f1f4000 nop dword [rax]
┌ 6: int sym.imp.puts (const char *s);
â”” â•Ž 0x00401030 ff25e22f0000 jmp qword [reloc.puts]
â•Ž 0x00401036 6800000000 push 0
└─< 0x0040103b e9e0ffffff jmp sym..plt
</code></pre>
<ul>
<li>At address <code>0x00401030</code> in the <code>.plt</code> section we see the indirect jump for
<code>puts</code> using the function pointer in <code>_GLOBAL_OFFSET_TABLE_[3] (GOT)</code>.</li>
<li><code>GOT[3]</code> initially points to instruction after the <code>puts</code> trampoline
<code>0x00401036</code>.</li>
<li>This pushes the relocation index <code>0</code> and then jumps to the first trampoline
<code>0x00401020</code>.</li>
<li>The first trampoline jumps to <code>GOT[2]</code> which will be filled at program
startup by the <code>ld.so</code> with its resolve function.</li>
<li>The <code>ld.so</code> resolve function fixes the relocation referenced by the
relocation index pushed by the <code>puts</code> trampoline.</li>
<li>The relocation entry at index <code>0</code> tells the resolve function which symbol to
search for and where to put the function pointer:
<pre><code class="language-makrdown"> > readelf -r <main>
>> Relocation section '.rela.plt' at offset 0x4b8 contains 1 entry:
>> Offset Info Type Sym. Value Sym. Name + Addend
>> 000000404018 000200000007 R_X86_64_JUMP_SLO 0000000000000000 puts@GLIBC_2.2.5 + 0
</code></pre>
As we can see the offset from relocation at index <code>0</code> points to <code>GOT[3]</code>.</li>
</ul>
<h1><a class="header" href="#arch" id="arch">Arch</a></h1>
<ul>
<li><a href="arch/./x86_64.html">x86_64</a></li>
<li><a href="arch/./arm64.html">arm64</a></li>
<li><a href="arch/./armv7.html">armv7</a></li>
</ul>
<h1><a class="header" href="#x86_64" id="x86_64">x86_64</a></h1>
<p>keywords: x86_64, x86, abi</p>
<ul>
<li>64bit synonyms: <code>x86_64</code>, <code>x64</code>, <code>amd64</code>, <code>intel 64</code></li>
<li>32bit synonyms: <code>x86</code>, <code>ia32</code>, <code>i386</code></li>
<li>ISA type: <code>CISC</code></li>
<li>Endianness: <code>little</code></li>
</ul>
<h2><a class="header" href="#registers" id="registers">Registers</a></h2>
<h3><a class="header" href="#general-purpose-register" id="general-purpose-register">General purpose register</a></h3>
<pre><code class="language-markdown">bytes
[7:0] [3:0] [1:0] [1] [0] desc
----------------------------------------------------------
rax eax ax ah al accumulator
rbx ebx bx bh bl base register
rcx ecx cx ch cl counter
rdx edx dx dh dl data register
rsi esi si - sil source index
rdi edi di - dil destination index
rbp ebp bp - bpl base pointer
rsp esp sp - spl stack pointer
r8-15 rNd rNw - rNb
</code></pre>
<h3><a class="header" href="#special-register" id="special-register">Special register</a></h3>
<pre><code class="language-markdown">bytes
[7:0] [3:0] [1:0] desc
---------------------------------------------------
rflags eflags flags flags register
rip eip ip instruction pointer
</code></pre>
<h3><a class="header" href="#flags-register" id="flags-register">FLAGS register</a></h3>
<pre><code class="language-markdown">rflags
bits desc
-----------------------------
[11] OF overflow flag
[10] DF direction flag
[7] SF sign flag
[6] ZF zero flag
[4] AF auxiliary carry flag
[2] PF parity flag
[0] CF carry flag
</code></pre>
<h2><a class="header" href="#addressing" id="addressing">Addressing</a></h2>
<pre><code class="language-asm">movw [rax], rbx // save val in rbx at [rax]
movw [imm], rbx // save val in rbx at [imm]
movw rax, [rbx+4*rcx] // load val at [rbx+4*rcx] into rax
</code></pre>
<p><code>rip</code> relative addressing:</p>
<pre><code class="language-asm">lea rax, [rip+.my_str] // load addr of .my_str into rax
...
.my_str:
.asciz "Foo"
</code></pre>
<h2><a class="header" href="#size-directives" id="size-directives">Size directives</a></h2>
<p>Explicitly specify size of the operation.</p>
<pre><code class="language-x86asm">mov byte ptr [rax], 0xff // save 1 byte(s) at [rax]
mov word ptr [rax], 0xff // save 2 byte(s) at [rax]
mov dword ptr [rax], 0xff // save 4 byte(s) at [rax]
mov qword ptr [rax], 0xff // save 8 byte(s) at [rax]
</code></pre>
<h2><a class="header" href="#a-hrefhttpswwwuclibcorgdocspsabi-x86_64pdfsysv-x86_64-abia" id="a-hrefhttpswwwuclibcorgdocspsabi-x86_64pdfsysv-x86_64-abia"><a href="https://www.uclibc.org/docs/psABI-x86_64.pdf">SysV x86_64 ABI</a></a></h2>
<h3><a class="header" href="#passing-arguments-to-functions" id="passing-arguments-to-functions">Passing arguments to functions</a></h3>
<ul>
<li>Integer/Pointer arguments
<pre><code class="language-markdown">reg arg
-----------
rdi 1
rsi 2
rdx 3
rcx 4
r8 5
r9 6
</code></pre>
</li>
<li>Floating point arguments
<pre><code class="language-markdown">reg arg
-----------
xmm0 1
.. ..
xmm7 8
</code></pre>
</li>
<li>Additional arguments are passed on the stack. Arguments are pushed
right-to-left (RTL), meaning next arguments are closer to current <code>rsp</code>.</li>
</ul>
<h3><a class="header" href="#return-values-from-functions" id="return-values-from-functions">Return values from functions</a></h3>
<ul>
<li>Integer/Pointer return values
<pre><code class="language-markdown">reg size
-----------------
rax 64 bit
rax+rdx 128 bit
</code></pre>
</li>
<li>Floating point return values:
<pre><code class="language-markdown">reg size
-------------------
xmm0 64 bit
xmm0+xmm1 128 bit
</code></pre>
</li>
</ul>
<h3><a class="header" href="#caller-saved-registers" id="caller-saved-registers">Caller saved registers</a></h3>
<p>Caller must save these registers if they should be preserved across function
calls.</p>
<ul>
<li><code>rax</code></li>
<li><code>rcx</code></li>
<li><code>rdx</code></li>
<li><code>rsi</code></li>
<li><code>rdi</code></li>
<li><code>rsp</code></li>
<li><code>r8</code> - <code>r11</code></li>
</ul>
<h3><a class="header" href="#callee-saved-registers" id="callee-saved-registers">Callee saved registers</a></h3>
<p>Caller can expect these registers to be preserved across function calls. Callee
must must save these registers in case they are used.</p>
<ul>
<li><code>rbx</code></li>
<li><code>rbp</code></li>
<li><code>r12</code> – <code>r15</code></li>
</ul>
<h3><a class="header" href="#stack" id="stack">Stack</a></h3>
<ul>
<li>grows downwards</li>
<li>frames aligned on 16 byte boundary
<pre><code class="language-text">Hi ADDR
| +------------+
| | prev frame |
| +------------+ <--- 16 byte aligned (X & ~0xf)
| [rbp+8] | saved RIP |
| [rbp] | saved RBP |
| [rbp-8] | func stack |
| | ... |
v +------------+
Lo ADDR
</code></pre>
</li>
</ul>
<h3><a class="header" href="#function-prologue--epilogue" id="function-prologue--epilogue">Function prologue & epilogue</a></h3>
<ul>
<li>prologue
<pre><code class="language-x86asm">push rbp // save caller base pointer
mov rbp, rsp // save caller stack pointer
</code></pre>
</li>
<li>epilogue
<pre><code class="language-x86asm">mov rsp, rbp // restore caller stack pointer
pop rbp // restore caller base pointer
</code></pre>
<blockquote>
<p>Equivalent to <code>leave</code> instruction.</p>
</blockquote>
</li>
</ul>
<h2><a class="header" href="#asm-skeleton" id="asm-skeleton">ASM skeleton</a></h2>
<p>Small assembler skeleton, ready to use with following properties:</p>
<ul>
<li>use raw Linux syscalls (<code>man 2 syscall</code> for ABI)</li>
<li>no <code>C runtime (crt)</code></li>
<li>gnu assembler <a href="https://sourceware.org/binutils/docs/as"><code>gas</code></a></li>
<li>intel syntax</li>
</ul>
<pre><code class="language-x86asm"># file: greet.s
.intel_syntax noprefix
.section .text, "ax", @progbits
.global _start
_start:
mov rdi, 1 # fd
lea rsi, [rip + greeting] # buf
mov rdx, [rip + greeting_len] # count
mov rax, 1 # write(2) syscall nr
syscall
mov rdi, 0 # exit code
mov rax, 60 # exit(2) syscall nr
syscall
.section .rdonly, "a", @progbits
greeting:
.asciz "Hi ASM-World!\n"
greeting_len:
.int .-greeting
</code></pre>
<blockquote>
<p>Syscall numbers are defined in <code>/usr/include/asm/unistd.h</code>.</p>
</blockquote>
<p>To compile and run:</p>
<pre><code class="language-bash">> gcc -o greet greet.s -nostartfiles -nostdlib && ./greet
Hi ASM-World!
</code></pre>
<h2><a class="header" href="#references-1" id="references-1">References</a></h2>
<ul>
<li><a href="https://www.uclibc.org/docs/psABI-x86_64.pdf">SystemV AMD64 ABI</a></li>
<li><a href="https://www.amd.com/system/files/TechDocs/24592.pdf">AMD64 Vol1: Application Programming</a></li>
<li><a href="https://www.amd.com/system/files/TechDocs/24593.pdf">AMD64 Vol2: System Programming</a></li>
<li><a href="https://www.amd.com/system/files/TechDocs/24594.pdf">AMD64 Vol3: General-Purpose & System Instructions</a></li>
<li><a href="https://cs.brown.edu/courses/cs033/docs/guides/x64_cheatsheet.pdf">X86_64 Cheat-Sheet</a></li>
<li><a href="https://software.intel.com/content/www/us/en/develop/download/intel-64-and-ia-32-architectures-software-developers-manual-volume-1-basic-architecture.html">Intel 64 Vol1: Basic Architecture</a></li>
<li><a href="https://software.intel.com/content/www/us/en/develop/download/intel-64-and-ia-32-architectures-sdm-combined-volumes-2a-2b-2c-and-2d-instruction-set-reference-a-z.html">Intel 64 Vol2: Instruction Set Reference</a></li>
<li><a href="https://software.intel.com/content/www/us/en/develop/download/intel-64-and-ia-32-architectures-sdm-combined-volumes-3a-3b-3c-and-3d-system-programming-guide.html">Intel 64 Vol3: System Programming Guide</a></li>
<li><a href="https://sourceware.org/binutils/docs/as">GNU Assembler</a></li>
<li><a href="https://sourceware.org/binutils/docs/as/Pseudo-Ops.html#Pseudo-Ops">GNU Assembler Directives</a></li>
<li><a href="https://sourceware.org/binutils/docs/as/i386_002dDependent.html">GNU Assembler <code>x86_64</code> dependent features</a></li>
</ul>
<h1><a class="header" href="#arm64" id="arm64">arm64</a></h1>
<p>keywords: arm64, aarch64, abi</p>
<ul>
<li>64bit synonyms: <code>arm64</code>, <code>aarch64</code></li>
<li>ISA type: <code>RISC</code></li>
<li>Endianness: <code>little</code>, <code>big</code></li>
</ul>
<h2><a class="header" href="#registers-1" id="registers-1">Registers</a></h2>
<h3><a class="header" href="#general-purpose-registers" id="general-purpose-registers">General purpose registers</a></h3>
<pre><code class="language-markdown">bytes
[7:0] [3:0] desc
---------------------------------------------
x0-x28 w0-w28 general purpose registers
x29 w29 frame pointer (FP)
x30 w30 link register (LR)
sp wsp stack pointer (SP)
pc program counter (PC)
xzr wzr zero register
</code></pre>
<blockquote>
<p>Write to <code>wN</code> register clears upper 32bit.</p>
</blockquote>
<h3><a class="header" href="#special-registers-per-el" id="special-registers-per-el">Special registers per EL</a></h3>
<pre><code class="language-markdown">bytes
[7:0] desc
---------------------------------------------
sp_el0 stack pointer EL0
sp_el1 stack pointer EL1
elr_el1 exception link register EL1
spsr_el1 saved process status register EL1
sp_el2 stack pointer EL2
elr_el2 exception link register EL2
spsr_el2 saved process status register EL2
sp_el3 stack pointer EL3
elr_el3 exception link register EL3
spsr_el3 saved process status register EL3
</code></pre>
<h2><a class="header" href="#instructions-cheatsheet" id="instructions-cheatsheet">Instructions cheatsheet</a></h2>
<h3><a class="header" href="#accessing-system-registers" id="accessing-system-registers">Accessing system registers</a></h3>
<p>Reading from system registers:</p>
<pre><code class="language-armasm">mrs x0, vbar_el1 // move vbar_el1 into x0
</code></pre>
<p>Writing to system registers:</p>
<pre><code class="language-armasm">msr vbar_el1, x0 // move x0 into vbar_el1
</code></pre>
<h3><a class="header" href="#control-flow-1" id="control-flow-1">Control Flow</a></h3>
<pre><code class="language-armasm">b <offset> // relative forward/back branch
br <Xn> // absolute branch to address in register Xn
// branch & link, store return address in X30 (LR)
bl <offset> // relative forward/back branch
blr <Xn> // absolute branch to address in register Xn
ret {Xn} // return to address in X30, or Xn if supplied
</code></pre>
<h2><a class="header" href="#addressing-1" id="addressing-1">Addressing</a></h2>
<h3><a class="header" href="#offset" id="offset">Offset</a></h3>
<pre><code class="language-armasm">ldr x0, [x1] // x0 = [x1]
ldr x0, [x1, 8] // x0 = [x1 + 8]
ldr x0, [x1, x2, lsl #3] // x0 = [x1 + (x2<<3)]
ldr x0, [x1, w2, stxw] // x0 = [x1 + sign_ext(w2)]
ldr x0, [x1, w2, stxw #3] // x0 = [x1 + (sign_ext(w2)<<3)]
</code></pre>
<blockquote>
<p>Shift amount can either be <code>0</code> or <code>log2(access_size_bytes)</code>. Eg for 8byte
access it can either be <code>{0, 3}</code>.</p>
</blockquote>
<h3><a class="header" href="#index" id="index">Index</a></h3>
<pre><code class="language-armasm">ldr x0, [x1, 8]! // pre-inc : x1+=8; x0 = [x1]
ldr x0, [x1], 8 // post-inc: x0 = [x1]; x1+=8
</code></pre>
<h3><a class="header" href="#pair-access" id="pair-access">Pair access</a></h3>
<pre><code class="language-armasm">ldp x1, x2, [x0] // x1 = [x0]; x2 = [x0 + 8]
stp x1, x2, [x0] // [x0] = x1; [x0 + 8] = x2
</code></pre>
<h2><a class="header" href="#procedure-call-standard-arm64-a-hrefhttpsgithubcomarm-softwareabi-aablobmasteraapcs64aapcs64rstaapcs64a" id="procedure-call-standard-arm64-a-hrefhttpsgithubcomarm-softwareabi-aablobmasteraapcs64aapcs64rstaapcs64a">Procedure Call Standard ARM64 (<a href="https://github.com/ARM-software/abi-aa/blob/master/aapcs64/aapcs64.rst"><code>aapcs64</code></a>)</a></h2>
<h3><a class="header" href="#passing-arguments-to-functions-1" id="passing-arguments-to-functions-1">Passing arguments to functions</a></h3>
<ul>
<li>Integer/Pointer arguments
<pre><code class="language-markdown">reg arg
-----------
x0 1
.. ..
x7 8
</code></pre>
</li>
<li>Additional arguments are passed on the stack. Arguments are pushed
<code>right-to-left (RTL)</code>, meaning next arguments are closer to current <code>sp</code>.
<pre><code class="language-markdown">void take(..., int a9, int a10);
| | | ... | Hi
| +-->| a10 | |
+---------->| a9 | <-SP |
+-----+ v
| ... | Lo
</code></pre>
</li>
</ul>
<h3><a class="header" href="#return-values-from-functions-1" id="return-values-from-functions-1">Return values from functions</a></h3>
<ul>
<li>Integer/Pointer return values
<pre><code class="language-markdown">reg size
-----------------
x0 64 bit
</code></pre>
</li>
</ul>
<h3><a class="header" href="#callee-saved-registers-1" id="callee-saved-registers-1">Callee saved registers</a></h3>
<ul>
<li><code>x19</code> - <code>x28</code></li>
<li><code>SP</code></li>
</ul>
<h3><a class="header" href="#stack-1" id="stack-1">Stack</a></h3>
<ul>
<li>full descending
<ul>
<li>full: <code>sp</code> points to the last used location (valid item)</li>
<li>descending: stack grows downwards</li>
</ul>
</li>
<li><code>sp</code> must be 16byte aligned when used to access memory for r/w</li>
<li><code>sp</code> must be 16byte aligned on public interface interfaces</li>
</ul>
<h3><a class="header" href="#frame-chain" id="frame-chain">Frame chain</a></h3>
<ul>
<li>linked list of stack-frames</li>
<li>each frame links to the frame of its caller by a <code>frame record</code>
<ul>
<li>a frame record is described as a <code>(FP,LR)</code> pair</li>
</ul>
</li>
<li><code>x29 (FP)</code> must point to the frame record of the current stack-frame
<pre><code class="language-markdown"> +------+ Hi
| 0 | frame0 |
+->| 0 | |
| | ... | |
| +------+ |
| | LR | frame1 |
+--| FP |<-+ |
| ... | | |
+------+ | |
| LR | | current |
x29 ->| FP |--+ frame v
| ... | Lo
</code></pre>
</li>
<li>end of the frame chain is indicated by following frame record <code>(0,-)</code></li>
<li>location of the frame record in the stack frame is not specified</li>
</ul>
<h3><a class="header" href="#function-prologue--epilogue-1" id="function-prologue--epilogue-1">Function prologue & epilogue</a></h3>
<ul>
<li>prologue
<pre><code class="language-armasm">sub sp, sp, 16
stp x29, x30, [sp] // [sp] = x29; [sp + 8] = x30
mov x29, sp // FP points to frame record
</code></pre>
</li>
<li>epilogue
<pre><code class="language-armasm">ldp x29, x30, [sp] // x29 = [sp]; x30 = [sp + 8]
add sp, sp, 16
ret
</code></pre>
</li>
</ul>
<h2><a class="header" href="#asm-skeleton-1" id="asm-skeleton-1">ASM skeleton</a></h2>
<p>Small assembler skeleton, ready to use with following properties:</p>
<ul>
<li>use raw Linux syscalls (<code>man 2 syscall</code> for ABI)</li>
<li>no <code>C runtime (crt)</code></li>
<li>gnu assembler <a href="https://sourceware.org/binutils/docs/as"><code>gas</code></a></li>
</ul>
<pre><code class="language-armasm">// file: greet.S
#include <asm/unistd.h> // syscall NRs
.arch armv8-a
.section .text, "ax", @progbits
.balign 4 // align code on 4byte boundary
.global _start
_start:
mov x0, 2 // fd
ldr x1, =greeting // buf
ldr x2, =greeting_len // &len
ldr x2, [x2] // len
mov w8, __NR_write // write(2) syscall
svc 0
mov x0, 0 // exit code
mov w8, __NR_exit // exit(2) syscall
svc 0
.balign 8 // align data on 8byte boundary
.section .rodata, "a", @progbits
greeting:
.asciz "Hi ASM-World!\n"
greeting_len:
.int .-greeting
</code></pre>
<blockquote>
<p>man gcc: <code>file.S</code> assembler code that must be preprocessed.</p>
</blockquote>
<p>To cross-compile and run:</p>
<pre><code class="language-bash">> aarch64-linux-gnu-g++ -o greet greet.S -nostartfiles -nostdlib \
-Wl,--dynamic-linker=/usr/aarch64-linux-gnu/lib/ld-linux-aarch64.so.1 \
&& qemu-aarch64 ./greet
Hi ASM-World!
</code></pre>
<blockquote>
<p>Cross-compiling on <code>Ubuntu 20.04 (x86_64)</code>, paths might differ on other
distributions. Explicitly specifying the dynamic linker should not be
required when compiling natively on arm64.</p>
</blockquote>
<h2><a class="header" href="#references-2" id="references-2">References</a></h2>
<ul>
<li><a href="https://github.com/ARM-software/abi-aa/blob/master/aapcs64/aapcs64.rst">Procedure Call Standard ARM64</a></li>
<li><a href="https://developer.arm.com/documentation/den0024/latest">ARMv8-A Programmer's Guide</a></li>
<li><a href="https://developer.arm.com/documentation/ddi0487/latest">ARMv8-A Architecture Reference Manual</a></li>
<li><a href="https://developer.arm.com/documentation/dai0527/latest">AppNote: ARMv8 Bare-metal boot code</a></li>
<li><a href="https://sourceware.org/binutils/docs/as">GNU Assembler</a></li>
<li><a href="https://sourceware.org/binutils/docs/as/Pseudo-Ops.html#Pseudo-Ops">GNU Assembler Directives</a></li>
<li><a href="https://sourceware.org/binutils/docs/as/AArch64_002dDependent.html">GNU Assembler <code>AArch64</code> dependent features</a></li>
</ul>
<h1><a class="header" href="#armv7a" id="armv7a">armv7a</a></h1>
<p>keywords: arm, armv7, abi</p>
<ul>
<li>ISA type: <code>RISC</code></li>
<li>Endianness: <code>little</code>, <code>big</code></li>
</ul>
<h2><a class="header" href="#registers-2" id="registers-2">Registers</a></h2>
<h3><a class="header" href="#general-purpose-registers-1" id="general-purpose-registers-1">General purpose registers</a></h3>
<pre><code class="language-markdown">bytes
[3:0] alt desc
---------------------------------------------
r0-r12 general purpose registers
r11 fp
r13 sp stack pointer
r14 lr link register
r15 pc program counter
</code></pre>
<h3><a class="header" href="#special-registers" id="special-registers">Special registers</a></h3>
<pre><code class="language-markdown">bytes
[3:0] desc
---------------------------------------------
cpsr current program status register
</code></pre>
<h3><a class="header" href="#cpsr-register" id="cpsr-register">CPSR register</a></h3>
<pre><code class="language-markdown">cpsr
bits desc
-----------------------------
[31] N negative flag
[30] Z zero flag
[29] C carry flag
[28] V overflow flag
[27] Q cummulative saturation (sticky)
[9] E load/store endianness
[8] A disable asynchronous aborts
[7] I disable IRQ
[6] F disable FIQ
[5] T indicate Thumb state
[4:0] M process mode (USR, FIQ, IRQ, SVC, ABT, UND, SYS)
</code></pre>
<h2><a class="header" href="#instructions-cheatsheet-1" id="instructions-cheatsheet-1">Instructions cheatsheet</a></h2>
<h3><a class="header" href="#accessing-system-registers-1" id="accessing-system-registers-1">Accessing system registers</a></h3>
<p>Reading from system registers:</p>
<pre><code class="language-armasm">mrs r0, cpsr // move cpsr into r0
</code></pre>
<p>Writing to system registers:</p>
<pre><code class="language-armasm">msr cpsr, r0 // move r0 into cpsr
</code></pre>
<h3><a class="header" href="#control-flow-2" id="control-flow-2">Control Flow</a></h3>
<pre><code class="language-armasm">b <lable> // relative forward/back branch
bl <lable> // relative forward/back branch & link return addr in r14 (LR)
// branch & exchange (can change between ARM & Thumb instruction set)
// bit Rm[0] == 0 -> ARM
// bit Rm[0] == 1 -> Thumb
bx <Rm> // absolute branch to address in register Rm
blx <Rm> // absolute branch to address in register Rm &
// link return addr in r14 (LR)
</code></pre>
<h3><a class="header" href="#loadstore" id="loadstore">Load/Store</a></h3>
<p>Different addressing modes.</p>
<pre><code class="language-armasm">str r1, [r0] // [r0]=r1
str r1, [r0, #4] // [r0+4]=r1
str r1, [r0, #4]! // r0+=4; [r0]=r1
str r1, [r0], 4 // [r0]=r1; r0+=4
</code></pre>
<p>Load/store multiple registers full-descending.</p>
<pre><code class="language-armasm">stmfd r0!, {r1-r2, r5} // r0-=4; [r0]=r5
// r0-=4; [r0]=r2
// r0-=4; [r0]=r1
ldmfd r0!, {r1-r2, r5} // r1=[r0]; r0+=4
// r2=[r0]; r0+=4
// r5=[r0]; r0+=4
</code></pre>
<blockquote>
<p><code>!</code> is optional but has the effect to update the base pointer register <code>r0</code> here.</p>
</blockquote>
<p>Push/Pop</p>
<pre><code class="language-armasm">push {r0-r2} // effectively stmfd sp!, {r0-r2}
pop {r0-r2} // effectively ldmfd sp!, {r0-r2}
</code></pre>
<h2><a class="header" href="#procedure-call-standard-arm-a-hrefhttpsgithubcomarm-softwareabi-aablobmasteraapcs32aapcs32rstaapcs32a" id="procedure-call-standard-arm-a-hrefhttpsgithubcomarm-softwareabi-aablobmasteraapcs32aapcs32rstaapcs32a">Procedure Call Standard ARM (<a href="https://github.com/ARM-software/abi-aa/blob/master/aapcs32/aapcs32.rst"><code>aapcs32</code></a>)</a></h2>
<h3><a class="header" href="#passing-arguments-to-functions-2" id="passing-arguments-to-functions-2">Passing arguments to functions</a></h3>
<ul>
<li>integer/pointer arguments
<pre><code class="language-markdown">reg arg
-----------
r0 1
.. ..
r3 4
</code></pre>
</li>
<li>a double word (64bit) is passed in two consecutive registers (eg <code>r1+r2</code>)</li>
<li>additional arguments are passed on the stack. Arguments are pushed
<code>right-to-left (RTL)</code>, meaning next arguments are closer to current <code>sp</code>.
<pre><code class="language-markdown">void take(..., int a5, int a6);
| | | ... | Hi
| +-->| a6 | |
+---------->| a5 | <-SP |
+-----+ v
| ... | Lo
</code></pre>
</li>
</ul>
<h3><a class="header" href="#return-values-from-functions-2" id="return-values-from-functions-2">Return values from functions</a></h3>
<ul>
<li>integer/pointer return values
<pre><code class="language-markdown">reg size
-----------------
r0 32 bit
r0+r1 64 bit
</code></pre>
</li>
</ul>
<h3><a class="header" href="#callee-saved-registers-2" id="callee-saved-registers-2">Callee saved registers</a></h3>
<ul>
<li><code>r4</code> - <code>r11</code></li>
<li><code>sp</code></li>
</ul>
<h3><a class="header" href="#stack-2" id="stack-2">Stack</a></h3>
<ul>
<li>full descending
<ul>
<li>full: <code>sp</code> points to the last used location (valid item)</li>
<li>descending: stack grows downwards</li>
</ul>
</li>
<li><code>sp</code> must be 4byte aligned (word boundary) at all time</li>
<li><code>sp</code> must be 8byte aligned on public interface interfaces</li>
</ul>
<h3><a class="header" href="#frame-chain-1" id="frame-chain-1">Frame chain</a></h3>
<ul>
<li>not strictly required by each platform</li>
<li>linked list of stack-frames</li>
<li>each frame links to the frame of its caller by a <code>frame record</code>
<ul>
<li>a frame record is described as a <code>(FP,LR)</code> pair (2x32bit)</li>
</ul>
</li>
<li><code>r11 (FP)</code> must point to the frame record of the current stack-frame
<pre><code class="language-markdown"> +------+ Hi
| 0 | frame0 |
+->| 0 | |
| | ... | |
| +------+ |
| | LR | frame1 |
+--| FP |<-+ |
| ... | | |
+------+ | |
| LR | | current |
r11 ->| FP |--+ frame v
| ... | Lo
</code></pre>
</li>
<li>end of the frame chain is indicated by following frame record <code>(0,-)</code></li>
<li>location of the frame record in the stack frame is not specified</li>
<li><code>r11</code> is not updated before the new frame record is fully constructed</li>
</ul>
<h3><a class="header" href="#function-prologue--epilogue-2" id="function-prologue--epilogue-2">Function prologue & epilogue</a></h3>
<ul>
<li>prologue
<pre><code class="language-armasm">push {fp, lr}
mov fp, sp // FP points to frame record
</code></pre>
</li>
<li>epilogue
<pre><code class="language-armasm">pop {fp, pc} // pop LR directly into PC
</code></pre>
</li>
</ul>
<h2><a class="header" href="#asm-skeleton-2" id="asm-skeleton-2">ASM skeleton</a></h2>
<p>Small assembler skeleton, ready to use with following properties:</p>
<ul>
<li>use raw Linux syscalls (<code>man 2 syscall</code> for ABI)</li>
<li>no <code>C runtime (crt)</code></li>
<li>gnu assembler <a href="https://sourceware.org/binutils/docs/as"><code>gas</code></a></li>
</ul>
<pre><code class="language-armasm">// file: greet.S
#include <asm/unistd.h> // syscall NRs
.arch armv7-a
.section .text, "ax"
.balign 4
// Emit `arm` instructions, same as `.arm` directive.
.code 32
.global _start
_start:
// Branch with link and exchange instruction set.
blx _do_greet
mov r0, #0 // exit code
mov r7, #__NR_exit // exit(2) syscall
swi 0x0
// Emit `thumb` instructions, same as `.thumb` directive.
.code 16
.thumb_func
_do_greet:
mov r0, #2 // fd
ldr r1, =greeting // buf
ldr r2, =greeting_len // &len
ldr r2, [r2] // len
mov r7, #__NR_write // write(2) syscall
swi 0x0
// Branch and exchange instruction set.
bx lr
.balign 8 // align data on 8byte boundary
.section .rodata, "a"
greeting:
.asciz "Hi ASM-World!\n"
greeting_len:
.int .-greeting
</code></pre>
<blockquote>
<p>man gcc: <code>file.S</code> assembler code that must be preprocessed.</p>
</blockquote>
<p>To cross-compile and run:</p>
<pre><code class="language-bash">> arm-linux-gnueabi-gcc -o greet greet.S -nostartfiles -nostdlib \
-Wl,--dynamic-linker=/usr/arm-linux-gnueabi/lib/ld-linux.so.3 \
&& qemu-arm ./greet
Hi ASM-World!
</code></pre>
<blockquote>
<p>Cross-compiling on <code>Ubuntu 20.04 (x86_64)</code>, paths might differ on other
distributions. Explicitly specifying the dynamic linker should not be
required when compiling natively on arm.</p>
</blockquote>
<h2><a class="header" href="#references-3" id="references-3">References</a></h2>
<ul>
<li><a href="https://github.com/ARM-software/abi-aa/blob/master/aapcs32/aapcs32.rst">Procedure Call Standard ARM</a></li>
<li><a href="https://developer.arm.com/documentation/den0013/latest">ARMv7-A Programmer's Guide</a></li>
<li><a href="https://developer.arm.com/documentation/ddi0406/latest">ARMv7-A Architecture Reference Manual</a></li>
<li><a href="https://sourceware.org/binutils/docs/as">GNU Assembler</a></li>
<li><a href="https://sourceware.org/binutils/docs/as/Pseudo-Ops.html#Pseudo-Ops">GNU Assembler Directives</a></li>
<li><a href="https://sourceware.org/binutils/docs/as/ARM_002dDependent.html">GNU Assembler <code>ARM</code> dependent features</a></li>
</ul>
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