diff options
Diffstat (limited to 'development/gas.html')
| -rw-r--r-- | development/gas.html | 83 |
1 files changed, 57 insertions, 26 deletions
diff --git a/development/gas.html b/development/gas.html index 3c87981..dd946bb 100644 --- a/development/gas.html +++ b/development/gas.html @@ -31,10 +31,11 @@ <!-- Custom theme stylesheets --> - <!-- Provide site root to javascript --> + <!-- Provide site root and default themes to javascript --> <script> - var path_to_root = "../"; - var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "navy" : "light"; + const path_to_root = "../"; + const default_light_theme = "light"; + const default_dark_theme = "navy"; </script> <!-- Start loading toc.js asap --> <script src="../toc.js"></script> @@ -44,8 +45,8 @@ <!-- Work around some values being stored in localStorage wrapped in quotes --> <script> try { - var theme = localStorage.getItem('mdbook-theme'); - var sidebar = localStorage.getItem('mdbook-sidebar'); + let theme = localStorage.getItem('mdbook-theme'); + let sidebar = localStorage.getItem('mdbook-sidebar'); if (theme.startsWith('"') && theme.endsWith('"')) { localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1)); @@ -59,7 +60,8 @@ <!-- Set the theme before any content is loaded, prevents flash --> <script> - var theme; + const default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? default_dark_theme : default_light_theme; + let theme; try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { } if (theme === null || theme === undefined) { theme = default_theme; } const html = document.documentElement; @@ -72,8 +74,8 @@ <!-- Hide / unhide sidebar before it is displayed --> <script> - var sidebar = null; - var sidebar_toggle = document.getElementById("sidebar-toggle-anchor"); + let sidebar = null; + const sidebar_toggle = document.getElementById("sidebar-toggle-anchor"); if (document.body.clientWidth >= 1080) { try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { } sidebar = sidebar || 'visible'; @@ -109,6 +111,7 @@ <i class="fa fa-paint-brush"></i> </button> <ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu"> + <li role="none"><button role="menuitem" class="theme" id="default_theme">Auto</button></li> <li role="none"><button role="menuitem" class="theme" id="light">Light</button></li> <li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li> <li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li> @@ -158,8 +161,18 @@ <h1 id="gas"><a class="header" href="#gas">gas</a></h1> <h2 id="frequently-used-directives"><a class="header" href="#frequently-used-directives">Frequently used directives</a></h2> <ul> -<li> -<p><code>.byte</code>, <code>.2byte</code>, <code>.4byte</code>, <code>.8byte</code> to define a N byte value</p> +<li><code>.section</code> to define a section (elf files) +<pre><code class="language-x86asm">.section .text.foo, "ax", @progbits +; defines section named .text.foo with alloc+exec perms + +.section .data.foo, "aw", @progbits +; defines section named .data.foo with alloc+write perms + +.section .rodata.foo, "a", @progbits +; defines section named .rodata.foo with alloc perms +</code></pre> +</li> +<li><code>.byte</code>, <code>.2byte</code>, <code>.4byte</code>, <code>.8byte</code> to define a N byte value <pre><code class="language-x86asm">.byte 0xaa .2byte 0xaabb .2byte 0xaa, 0xbb @@ -167,19 +180,16 @@ .8byte 0xaabbccdd11223344 </code></pre> </li> -<li> -<p><code>.ascii</code> to define an ascii string</p> +<li><code>.ascii</code> to define an ascii string <pre><code class="language-x86asm">.ascii "foo" ; allocates 3 bytes </code></pre> </li> -<li> -<p><code>.asciz</code> to define an ascii string with <code>'\0'</code> terminator</p> +<li><code>.asciz</code> to define an ascii string with <code>'\0'</code> terminator <pre><code class="language-x86asm">.asciz "foo" ; allocates 4 bytes (str + \0) </code></pre> </li> -<li> -<p><code>.macro</code> to define assembler macros. Arguments are accessed with the -<code>\arg</code> syntax.</p> +<li><code>.macro</code> to define assembler macros. Arguments are accessed with the +<code>\arg</code> syntax. <pre><code class="language-x86asm">.macro defstr name str \name: .ascii "\str" @@ -194,16 +204,37 @@ defstr foo, "foobar" <p>Use <code>\()</code> to concatenate macro argument and literal.</p> </blockquote> </li> -<li> -<p><a href="https://sourceware.org/binutils/docs/as">GNU Assembler</a></p> -</li> -<li> -<p><a href="https://sourceware.org/binutils/docs/as/Pseudo-Ops.html#Pseudo-Ops">GNU Assembler Directives</a></p> +<li><code>.rept</code> to repeat a sequence of lines between <code>.rept</code> and <code>.endr</code>. +<pre><code class="language-x86asm">.rept 4 +.4byte 123 +.endr +</code></pre> </li> -<li> -<p><a href="https://sourceware.org/binutils/docs/as/i386_002dDependent.html">GNU Assembler <code>x86_64</code> dependent features</a></p> +<li><code>.fill cnt, elem_size, val</code> write <code>cnt</code> times <code>val</code> with element size <code>elem_size</code>. For example one can use it to create a mbr boot record (magic number 0xaa55 at byte 511, 512). +<pre><code class="language-x86asm">.section .boot, "ax", @progbits +; some code .. +.4byte 0xff + +.fill 510 - (. - .boot), 1, 0x00 +.2byte 0xaa55 + +; as foo.s && objdump -j .boot -s +; Contents of section .boot: +; 0000 ff000000 00000000 00000000 00000000 +; .. +; 01f0 00000000 00000000 00000000 000055aa +</code></pre> +<blockquote> +<p>Here <code>.</code> stands for the current location counter.</p> +</blockquote> </li> </ul> +<h2 id="references"><a class="header" href="#references">References</a></h2> +<ul> +<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> </main> @@ -213,7 +244,7 @@ defstr foo, "foobar" <i class="fa fa-angle-left"></i> </a> - <a rel="next prefetch" href="../development/git.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> + <a rel="next prefetch" href="../development/ld.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> <i class="fa fa-angle-right"></i> </a> @@ -227,7 +258,7 @@ defstr foo, "foobar" <i class="fa fa-angle-left"></i> </a> - <a rel="next prefetch" href="../development/git.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> + <a rel="next prefetch" href="../development/ld.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> <i class="fa fa-angle-right"></i> </a> </nav> |