<!DOCTYPE HTML> <html lang="en" class="sidebar-visible no-js light"> <head> <!-- Book generated using mdBook --> <meta charset="UTF-8"> <title>x86_64 - Notes</title> <!-- Custom HTML head --> <meta content="text/html; charset=utf-8" http-equiv="Content-Type"> <meta name="description" content=""> <meta name="viewport" content="width=device-width, initial-scale=1"> <meta name="theme-color" content="#ffffff" /> <link rel="icon" href="../favicon.svg"> <link rel="shortcut icon" href="../favicon.png"> <link rel="stylesheet" href="../css/variables.css"> <link rel="stylesheet" href="../css/general.css"> <link rel="stylesheet" href="../css/chrome.css"> <link rel="stylesheet" href="../css/print.css" media="print"> <!-- Fonts --> <link rel="stylesheet" href="../FontAwesome/css/font-awesome.css"> <link rel="stylesheet" href="../fonts/fonts.css"> <!-- Highlight.js Stylesheets --> <link rel="stylesheet" href="../highlight.css"> <link rel="stylesheet" href="../tomorrow-night.css"> <link rel="stylesheet" href="../ayu-highlight.css"> <!-- Custom theme stylesheets --> </head> <body> <!-- Provide site root to javascript --> <script type="text/javascript"> var path_to_root = "../"; var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? 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href="../tools/fish.html"><strong aria-hidden="true">1.3.</strong> fish</a></li><li class="chapter-item expanded "><a href="../tools/tmux.html"><strong aria-hidden="true">1.4.</strong> tmux</a></li><li class="chapter-item expanded "><a href="../tools/git.html"><strong aria-hidden="true">1.5.</strong> git</a></li><li class="chapter-item expanded "><a href="../tools/awk.html"><strong aria-hidden="true">1.6.</strong> awk</a></li><li class="chapter-item expanded "><a href="../tools/emacs.html"><strong aria-hidden="true">1.7.</strong> emacs</a></li><li class="chapter-item expanded "><a href="../tools/gpg.html"><strong aria-hidden="true">1.8.</strong> gpg</a></li><li class="chapter-item expanded "><a href="../tools/gdb.html"><strong aria-hidden="true">1.9.</strong> gdb</a></li><li class="chapter-item expanded "><a href="../tools/gdbserver.html"><strong aria-hidden="true">1.10.</strong> gdbserver</a></li><li class="chapter-item expanded "><a href="../tools/radare2.html"><strong aria-hidden="true">1.11.</strong> radare2</a></li><li class="chapter-item expanded "><a href="../tools/qemu.html"><strong aria-hidden="true">1.12.</strong> qemu</a></li><li class="chapter-item expanded "><a href="../tools/pacman.html"><strong aria-hidden="true">1.13.</strong> pacman</a></li><li class="chapter-item expanded "><a href="../tools/dot.html"><strong aria-hidden="true">1.14.</strong> dot</a></li></ol></li><li class="chapter-item expanded "><a href="../monitor/index.html"><strong aria-hidden="true">2.</strong> Resource analysis & monitor</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../monitor/lsof.html"><strong aria-hidden="true">2.1.</strong> lsof</a></li><li class="chapter-item expanded "><a href="../monitor/ss.html"><strong aria-hidden="true">2.2.</strong> ss</a></li><li class="chapter-item expanded "><a href="../monitor/pidstat.html"><strong aria-hidden="true">2.3.</strong> pidstat</a></li><li class="chapter-item expanded "><a href="../monitor/pgrep.html"><strong aria-hidden="true">2.4.</strong> pgrep</a></li><li class="chapter-item expanded "><a href="../monitor/pmap.html"><strong aria-hidden="true">2.5.</strong> pmap</a></li><li class="chapter-item expanded "><a href="../monitor/pstack.html"><strong aria-hidden="true">2.6.</strong> pstack</a></li></ol></li><li class="chapter-item expanded "><a href="../trace_profile/index.html"><strong aria-hidden="true">3.</strong> Trace and Profile</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../trace_profile/strace.html"><strong aria-hidden="true">3.1.</strong> strace</a></li><li class="chapter-item expanded "><a href="../trace_profile/ltrace.html"><strong aria-hidden="true">3.2.</strong> ltrace</a></li><li class="chapter-item expanded "><a href="../trace_profile/perf.html"><strong aria-hidden="true">3.3.</strong> perf</a></li><li class="chapter-item expanded "><a href="../trace_profile/oprofile.html"><strong aria-hidden="true">3.4.</strong> OProfile</a></li><li class="chapter-item expanded "><a href="../trace_profile/time.html"><strong aria-hidden="true">3.5.</strong> time</a></li></ol></li><li class="chapter-item expanded "><a href="../binary/index.html"><strong aria-hidden="true">4.</strong> Binary</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../binary/od.html"><strong aria-hidden="true">4.1.</strong> od</a></li><li class="chapter-item expanded "><a href="../binary/xxd.html"><strong aria-hidden="true">4.2.</strong> xxd</a></li><li class="chapter-item expanded "><a href="../binary/readelf.html"><strong aria-hidden="true">4.3.</strong> readelf</a></li><li class="chapter-item expanded "><a href="../binary/objdump.html"><strong aria-hidden="true">4.4.</strong> objdump</a></li><li class="chapter-item expanded "><a href="../binary/nm.html"><strong aria-hidden="true">4.5.</strong> nm</a></li></ol></li><li class="chapter-item expanded "><a href="../development/index.html"><strong aria-hidden="true">5.</strong> Development</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../development/c++filt.html"><strong aria-hidden="true">5.1.</strong> c++filt</a></li><li class="chapter-item expanded "><a href="../development/c++.html"><strong aria-hidden="true">5.2.</strong> c++</a></li><li class="chapter-item expanded "><a href="../development/glibc.html"><strong aria-hidden="true">5.3.</strong> glibc</a></li><li class="chapter-item expanded "><a href="../development/gcc.html"><strong aria-hidden="true">5.4.</strong> gcc</a></li><li class="chapter-item expanded "><a href="../development/make.html"><strong aria-hidden="true">5.5.</strong> make</a></li><li class="chapter-item expanded "><a href="../development/ld.so.html"><strong aria-hidden="true">5.6.</strong> ld.so</a></li><li class="chapter-item expanded "><a href="../development/symbolver.html"><strong aria-hidden="true">5.7.</strong> symbol versioning</a></li><li class="chapter-item expanded "><a href="../development/python.html"><strong aria-hidden="true">5.8.</strong> python</a></li></ol></li><li class="chapter-item expanded "><a href="../linux/index.html"><strong aria-hidden="true">6.</strong> Linux</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../linux/systemd.html"><strong aria-hidden="true">6.1.</strong> systemd</a></li><li class="chapter-item expanded "><a href="../linux/coredump.html"><strong aria-hidden="true">6.2.</strong> coredump</a></li><li class="chapter-item expanded "><a href="../linux/ptrace_scope.html"><strong aria-hidden="true">6.3.</strong> ptrace_scope</a></li><li class="chapter-item expanded "><a href="../linux/cryptsetup.html"><strong aria-hidden="true">6.4.</strong> cryptsetup</a></li><li class="chapter-item expanded "><a href="../linux/swap.html"><strong aria-hidden="true">6.5.</strong> swap</a></li></ol></li><li class="chapter-item expanded "><a href="../network/index.html"><strong aria-hidden="true">7.</strong> Network</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../network/tcpdump.html"><strong aria-hidden="true">7.1.</strong> tcpdump</a></li></ol></li><li class="chapter-item expanded "><a href="../web/index.html"><strong aria-hidden="true">8.</strong> Web</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../web/html.html"><strong aria-hidden="true">8.1.</strong> html</a></li></ol></li><li class="chapter-item expanded "><a href="../arch/index.html"><strong aria-hidden="true">9.</strong> Arch</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../arch/x86_64.html" class="active"><strong aria-hidden="true">9.1.</strong> x86_64</a></li><li class="chapter-item expanded "><a href="../arch/arm64.html"><strong aria-hidden="true">9.2.</strong> arm64</a></li><li class="chapter-item expanded "><a href="../arch/armv7.html"><strong aria-hidden="true">9.3.</strong> armv7</a></li><li class="chapter-item expanded "><a href="../arch/riscv.html"><strong aria-hidden="true">9.4.</strong> riscv</a></li></ol></li></ol> </div> <div id="sidebar-resize-handle" class="sidebar-resize-handle"></div> </nav> <div id="page-wrapper" class="page-wrapper"> <div class="page"> <div id="menu-bar-hover-placeholder"></div> <div id="menu-bar" class="menu-bar sticky bordered"> <div class="left-buttons"> <button id="sidebar-toggle" class="icon-button" type="button" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar"> <i class="fa fa-bars"></i> </button> <button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list"> <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" 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(Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar"> <i class="fa fa-search"></i> </button> </div> <h1 class="menu-title">Notes</h1> <div class="right-buttons"> <a href="../print.html" title="Print this book" aria-label="Print this book"> <i id="print-button" class="fa fa-print"></i> </a> <a href="https://github.com/johannst/notes" title="Git repository" aria-label="Git repository"> <i id="git-repository-button" class="fa fa-github"></i> </a> </div> </div> <div id="search-wrapper" class="hidden"> <form id="searchbar-outer" class="searchbar-outer"> <input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header"> </form> <div id="searchresults-outer" class="searchresults-outer hidden"> <div id="searchresults-header" class="searchresults-header"></div> <ul id="searchresults"> </ul> </div> </div> <!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM --> <script type="text/javascript"> document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible'); document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible'); Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) { link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1); }); </script> <div id="content" class="content"> <main> <h1 id="x86_64"><a class="header" href="#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 id="registers"><a class="header" href="#registers">Registers</a></h2> <h3 id="general-purpose-register"><a class="header" href="#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 id="special-register"><a class="header" href="#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 id="flags-register"><a class="header" href="#flags-register">FLAGS register</a></h3> <pre><code class="language-markdown">rflags bits desc instr comment -------------------------------------------------------------------------------------------------------------- [21] ID identification ability to set/clear -> indicates support for CPUID instr [18] AC alignment check alignment exception for PL 3 (user), requires CR0.AM [13:12] IOPL io privilege level [11] OF overflow flag [10] DF direction flag cld/std increment (0) or decrement (1) registers in string operations [9] IF interrupt enable cli/sti [7] SF sign flag [6] ZF zero flag [4] AF auxiliary carry flag [2] PF parity flag [0] CF carry flag </code></pre> <p>Change flag bits with <code>pushf</code> / <code>popf</code> instructions:</p> <pre><code class="language-x86asm">pushfd // push flags (4bytes) onto stack or dword ptr [esp], (1 << 18) // enable AC flag popfd // pop flags (4byte) from stack </code></pre> <blockquote> <p>There is also <code>pushfq</code> / <code>popfq</code> to push and pop all 8 bytes of <code>rflags</code>.</p> </blockquote> <h3 id="model-specific-register-msr"><a class="header" href="#model-specific-register-msr">Model Specific Register (MSR)</a></h3> <pre><code class="language-x86asm">rdmsr // Read MSR register, effectively does EDX:EAX <- MSR[ECX] wrmsr // Write MSR register, effectively does MSR[ECX] <- EDX:EAX </code></pre> <h2 id="size-directives"><a class="header" href="#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 id="addressing"><a class="header" href="#addressing">Addressing</a></h2> <pre><code class="language-x86asm">mov qword ptr [rax], rbx // save val in rbx at [rax] mov qword ptr [imm], rbx // save val in rbx at [imm] mov rax, qword ptr [rbx+4*rcx] // load val at [rbx+4*rcx] into rax </code></pre> <p><code>rip</code> relative addressing:</p> <pre><code class="language-x86asm">lea rax, [rip+.my_str] // load addr of .my_str into rax ... .my_str: .asciz "Foo" </code></pre> <h2 id="string-instructions"><a class="header" href="#string-instructions">String instructions</a></h2> <p>The operand size of a string instruction is defined by the instruction suffix <code>b | w | d | q</code>.</p> <p>Source and destination registers are modified according to the <code>direction flag (DF)</code> in the <code>flags</code> register</p> <ul> <li><code>DF=0</code> increment src/dest registers</li> <li><code>DF=1</code> decrement src/dest registers</li> </ul> <p>Following explanation assumes <code>byte</code> operands with <code>DF=0</code>:</p> <pre><code class="language-x86asm">movsb // move data from string to string // ES:[DI] <- DS:[SI] // DI <- DI + 1 // SI <- SI + 1 lodsb // load string // AL <- DS:[SI] // SI <- SI + 1 stosb // store string // ES:[DI] <- AL // DI <- DI + 1 cmpsb // compare string operands // DS:[SI] - ES:[DI] ; set status flag (eg ZF) // SI <- SI + 1 // DI <- DI + 1 scasb // scan string // AL - ES:[DI] ; set status flag (eg ZF) // DI <- DI + 1 </code></pre> <p>String operations can be repeated:</p> <pre><code class="language-x86asm">rep // repeat until rcx = 0 repz // repeat until rcx = 0 or while ZF = 0 repnz // repeat until rcx = 0 or while ZF = 1 </code></pre> <h3 id="example-simple-memset"><a class="header" href="#example-simple-memset">Example: Simple <code>memset</code></a></h3> <pre><code class="language-x86asm">// memset (dest, 0xaa /* char */, 0x10 /* len */) lea di, [dest] mov al, 0xaa mov cx, 0x10 rep stosb </code></pre> <h2 id="sysv-x86_64-abi"><a class="header" href="#sysv-x86_64-abi"><a href="https://www.uclibc.org/docs/psABI-x86_64.pdf">SysV x86_64 ABI</a></a></h2> <h3 id="passing-arguments-to-functions"><a class="header" href="#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 id="return-values-from-functions"><a class="header" href="#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 id="caller-saved-registers"><a class="header" href="#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 id="callee-saved-registers"><a class="header" href="#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 id="stack"><a class="header" href="#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 id="function-prologue--epilogue"><a class="header" href="#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 id="asm-skeleton"><a class="header" href="#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 id="references"><a class="header" href="#references">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> </main> <nav class="nav-wrapper" aria-label="Page navigation"> <!-- Mobile navigation buttons --> <a rel="prev" href="../arch/index.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> <i class="fa fa-angle-left"></i> </a> <a rel="next" href="../arch/arm64.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> <i class="fa fa-angle-right"></i> </a> <div style="clear: both"></div> </nav> </div> </div> <nav class="nav-wide-wrapper" aria-label="Page navigation"> <a rel="prev" href="../arch/index.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> <i class="fa fa-angle-left"></i> </a> <a rel="next" href="../arch/arm64.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> <i class="fa fa-angle-right"></i> </a> </nav> </div> <script type="text/javascript"> window.playground_copyable = true; </script> <script src="../elasticlunr.min.js" type="text/javascript" charset="utf-8"></script> <script src="../mark.min.js" type="text/javascript" charset="utf-8"></script> <script src="../searcher.js" type="text/javascript" charset="utf-8"></script> <script src="../clipboard.min.js" type="text/javascript" charset="utf-8"></script> <script src="../highlight.js" type="text/javascript" charset="utf-8"></script> <script src="../book.js" type="text/javascript" charset="utf-8"></script> <!-- Custom JS scripts --> </body> </html>