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| author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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| committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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diff --git a/share/doc/gdb/Machine-Code.html b/share/doc/gdb/Machine-Code.html new file mode 100644 index 0000000..129b02f --- /dev/null +++ b/share/doc/gdb/Machine-Code.html @@ -0,0 +1,444 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1988-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "Free Software" and "Free Software Needs +Free Documentation", with the Front-Cover Texts being "A GNU Manual," +and with the Back-Cover Texts as in (a) below. + +(a) The FSF's Back-Cover Text is: "You are free to copy and modify +this GNU Manual. Buying copies from GNU Press supports the FSF in +developing GNU and promoting software freedom." --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>Debugging with GDB: Machine Code</title> + +<meta name="description" content="Debugging with GDB: Machine Code"> +<meta name="keywords" content="Debugging with GDB: Machine Code"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Source.html#Source" rel="up" title="Source"> +<link href="Disable-Reading-Source.html#Disable-Reading-Source" rel="next" title="Disable Reading Source"> +<link href="Source-Path.html#Source-Path" rel="previous" title="Source Path"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Machine-Code"></a> +<div class="header"> +<p> +Next: <a href="Disable-Reading-Source.html#Disable-Reading-Source" accesskey="n" rel="next">Disable Reading Source</a>, Previous: <a href="Source-Path.html#Source-Path" accesskey="p" rel="previous">Source Path</a>, Up: <a href="Source.html#Source" accesskey="u" rel="up">Source</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Source-and-Machine-Code"></a> +<h3 class="section">9.6 Source and Machine Code</h3> +<a name="index-source-line-and-its-code-address"></a> + +<p>You can use the command <code>info line</code> to map source lines to program +addresses (and vice versa), and the command <code>disassemble</code> to display +a range of addresses as machine instructions. You can use the command +<code>set disassemble-next-line</code> to set whether to disassemble next +source line when execution stops. When run under <small>GNU</small> Emacs +mode, the <code>info line</code> command causes the arrow to point to the +line specified. Also, <code>info line</code> prints addresses in symbolic form as +well as hex. +</p> +<dl compact="compact"> +<dd><a name="index-info-line"></a> +</dd> +<dt><code>info line</code></dt> +<dt><code>info line <var>locspec</var></code></dt> +<dd><p>Print the starting and ending addresses of the compiled code for the +source lines of the code locations that result from resolving +<var>locspec</var>. See <a href="Location-Specifications.html#Location-Specifications">Location Specifications</a>, for the various forms +of <var>locspec</var>. +With no <var>locspec</var>, information about the current source line is +printed. +</p></dd> +</dl> + +<p>For example, we can use <code>info line</code> to discover the location of +the object code for the first line of function +<code>m4_changequote</code>: +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) info line m4_changequote +Line 895 of "builtin.c" starts at pc 0x634c <m4_changequote> and \ + ends at 0x6350 <m4_changequote+4>. +</pre></div> + +<a name="index-code-address-and-its-source-line"></a> +<p>We can also inquire, using <code>*<var>addr</var></code> as the form for +<var>locspec</var>, what source line covers a particular address +<var>addr</var>: +</p><div class="smallexample"> +<pre class="smallexample">(gdb) info line *0x63ff +Line 926 of "builtin.c" starts at pc 0x63e4 <m4_changequote+152> and \ + ends at 0x6404 <m4_changequote+184>. +</pre></div> + +<a name="index-_0024_005f-and-info-line"></a> +<a name="index-x-command_002c-default-address"></a> +<a name="index-x_0028examine_0029_002c-and-info-line"></a> +<p>After <code>info line</code>, the default address for the <code>x</code> command +is changed to the starting address of the line, so that ‘<samp>x/i</samp>’ is +sufficient to begin examining the machine code (see <a href="Memory.html#Memory">Examining Memory</a>). Also, this address is saved as the value of the +convenience variable <code>$_</code> (see <a href="Convenience-Vars.html#Convenience-Vars">Convenience +Variables</a>). +</p> +<a name="index-info-line_002c-repeated-calls"></a> +<p>After <code>info line</code>, using <code>info line</code> again without +specifying a location will display information about the next source +line. +</p> +<a name="disassemble"></a><dl compact="compact"> +<dd><a name="index-disassemble"></a> +<a name="index-assembly-instructions"></a> +<a name="index-instructions_002c-assembly"></a> +<a name="index-machine-instructions"></a> +<a name="index-listing-machine-instructions"></a> +</dd> +<dt><code>disassemble</code></dt> +<dt><code>disassemble /m</code></dt> +<dt><code>disassemble /s</code></dt> +<dt><code>disassemble /r</code></dt> +<dt><code>disassemble /b</code></dt> +<dd><p>This specialized command dumps a range of memory as machine +instructions. It can also print mixed source+disassembly by specifying +the <code>/m</code> or <code>/s</code> modifier and print the raw instructions in +hex as well as in symbolic form by specifying the <code>/r</code> or <code>/b</code> +modifier. The default memory range is the function surrounding the +program counter of the selected frame. A single argument to this +command is a program counter value; <small>GDB</small> dumps the function +surrounding this value. When two arguments are given, they should be +separated by a comma, possibly surrounded by whitespace. The arguments +specify a range of addresses to dump, in one of two forms: +</p> +<dl compact="compact"> +<dt><code><var>start</var>,<var>end</var></code></dt> +<dd><p>the addresses from <var>start</var> (inclusive) to <var>end</var> (exclusive) +</p></dd> +<dt><code><var>start</var>,+<var>length</var></code></dt> +<dd><p>the addresses from <var>start</var> (inclusive) to +<code><var>start</var>+<var>length</var></code> (exclusive). +</p></dd> +</dl> + +<p>When 2 arguments are specified, the name of the function is also +printed (since there could be several functions in the given range). +</p> +<p>The argument(s) can be any expression yielding a numeric value, such as +‘<samp>0x32c4</samp>’, ‘<samp>&main+10</samp>’ or ‘<samp>$pc - 8</samp>’. +</p> +<p>If the range of memory being disassembled contains current program counter, +the instruction at that location is shown with a <code>=></code> marker. +</p></dd> +</dl> + +<p>The following example shows the disassembly of a range of addresses of +HP PA-RISC 2.0 code: +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) disas 0x32c4, 0x32e4 +Dump of assembler code from 0x32c4 to 0x32e4: + 0x32c4 <main+204>: addil 0,dp + 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26 + 0x32cc <main+212>: ldil 0x3000,r31 + 0x32d0 <main+216>: ble 0x3f8(sr4,r31) + 0x32d4 <main+220>: ldo 0(r31),rp + 0x32d8 <main+224>: addil -0x800,dp + 0x32dc <main+228>: ldo 0x588(r1),r26 + 0x32e0 <main+232>: ldil 0x3000,r31 +End of assembler dump. +</pre></div> + +<p>The following two examples are for RISC-V, and demonstrates the +difference between the <code>/r</code> and <code>/b</code> modifiers. First with +<code>/b</code>, the bytes of the instruction are printed, in hex, in memory +order: +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) disassemble /b 0x00010150,0x0001015c +Dump of assembler code from 0x10150 to 0x1015c: + 0x00010150 <call_me+4>: 22 dc sw s0,56(sp) + 0x00010152 <call_me+6>: 80 00 addi s0,sp,64 + 0x00010154 <call_me+8>: 23 26 a4 fe sw a0,-20(s0) + 0x00010158 <call_me+12>: 23 24 b4 fe sw a1,-24(s0) +End of assembler dump. +</pre></div> + +<p>In contrast, with <code>/r</code> the bytes of the instruction are displayed +in the instruction order, for RISC-V this means that the bytes have been +swapped to little-endian order: +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) disassemble /r 0x00010150,0x0001015c +Dump of assembler code from 0x10150 to 0x1015c: + 0x00010150 <call_me+4>: dc22 sw s0,56(sp) + 0x00010152 <call_me+6>: 0080 addi s0,sp,64 + 0x00010154 <call_me+8>: fea42623 sw a0,-20(s0) + 0x00010158 <call_me+12>: feb42423 sw a1,-24(s0) +End of assembler dump. +</pre></div> + +<p>Here is an example showing mixed source+assembly for Intel x86 +with <code>/m</code> or <code>/s</code>, when the program is stopped just after +function prologue in a non-optimized function with no inline code. +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) disas /m main +Dump of assembler code for function main: +5 { + 0x08048330 <+0>: push %ebp + 0x08048331 <+1>: mov %esp,%ebp + 0x08048333 <+3>: sub $0x8,%esp + 0x08048336 <+6>: and $0xfffffff0,%esp + 0x08048339 <+9>: sub $0x10,%esp + +6 printf ("Hello.\n"); +=> 0x0804833c <+12>: movl $0x8048440,(%esp) + 0x08048343 <+19>: call 0x8048284 <puts@plt> + +7 return 0; +8 } + 0x08048348 <+24>: mov $0x0,%eax + 0x0804834d <+29>: leave + 0x0804834e <+30>: ret + +End of assembler dump. +</pre></div> + +<p>The <code>/m</code> option is deprecated as its output is not useful when +there is either inlined code or re-ordered code. +The <code>/s</code> option is the preferred choice. +Here is an example for AMD x86-64 showing the difference between +<code>/m</code> output and <code>/s</code> output. +This example has one inline function defined in a header file, +and the code is compiled with ‘<samp>-O2</samp>’ optimization. +Note how the <code>/m</code> output is missing the disassembly of +several instructions that are present in the <code>/s</code> output. +</p> +<p><samp>foo.h</samp>: +</p> +<div class="smallexample"> +<pre class="smallexample">int +foo (int a) +{ + if (a < 0) + return a * 2; + if (a == 0) + return 1; + return a + 10; +} +</pre></div> + +<p><samp>foo.c</samp>: +</p> +<div class="smallexample"> +<pre class="smallexample">#include "foo.h" +volatile int x, y; +int +main () +{ + x = foo (y); + return 0; +} +</pre></div> + +<div class="smallexample"> +<pre class="smallexample">(gdb) disas /m main +Dump of assembler code for function main: +5 { + +6 x = foo (y); + 0x0000000000400400 <+0>: mov 0x200c2e(%rip),%eax # 0x601034 <y> + 0x0000000000400417 <+23>: mov %eax,0x200c13(%rip) # 0x601030 <x> + +7 return 0; +8 } + 0x000000000040041d <+29>: xor %eax,%eax + 0x000000000040041f <+31>: retq + 0x0000000000400420 <+32>: add %eax,%eax + 0x0000000000400422 <+34>: jmp 0x400417 <main+23> + +End of assembler dump. +(gdb) disas /s main +Dump of assembler code for function main: +foo.c: +5 { +6 x = foo (y); + 0x0000000000400400 <+0>: mov 0x200c2e(%rip),%eax # 0x601034 <y> + +foo.h: +4 if (a < 0) + 0x0000000000400406 <+6>: test %eax,%eax + 0x0000000000400408 <+8>: js 0x400420 <main+32> + +6 if (a == 0) +7 return 1; +8 return a + 10; + 0x000000000040040a <+10>: lea 0xa(%rax),%edx + 0x000000000040040d <+13>: test %eax,%eax + 0x000000000040040f <+15>: mov $0x1,%eax + 0x0000000000400414 <+20>: cmovne %edx,%eax + +foo.c: +6 x = foo (y); + 0x0000000000400417 <+23>: mov %eax,0x200c13(%rip) # 0x601030 <x> + +7 return 0; +8 } + 0x000000000040041d <+29>: xor %eax,%eax + 0x000000000040041f <+31>: retq + +foo.h: +5 return a * 2; + 0x0000000000400420 <+32>: add %eax,%eax + 0x0000000000400422 <+34>: jmp 0x400417 <main+23> +End of assembler dump. +</pre></div> + +<p>Here is another example showing raw instructions in hex for AMD x86-64, +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) disas /r 0x400281,+10 +Dump of assembler code from 0x400281 to 0x40028b: + 0x0000000000400281: 38 36 cmp %dh,(%rsi) + 0x0000000000400283: 2d 36 34 2e 73 sub $0x732e3436,%eax + 0x0000000000400288: 6f outsl %ds:(%rsi),(%dx) + 0x0000000000400289: 2e 32 00 xor %cs:(%rax),%al +End of assembler dump. +</pre></div> + +<p>Note that the ‘<samp>disassemble</samp>’ command’s address arguments are +specified using expressions in your programming language +(see <a href="Expressions.html#Expressions">Expressions</a>), not location specs +(see <a href="Location-Specifications.html#Location-Specifications">Location Specifications</a>). So, for example, if you want to +disassemble function <code>bar</code> in file <samp>foo.c</samp>, you must type +‘<samp>disassemble 'foo.c'::bar</samp>’ and not ‘<samp>disassemble foo.c:bar</samp>’. +</p> +<p>Some architectures have more than one commonly-used set of instruction +mnemonics or other syntax. +</p> +<p>For programs that were dynamically linked and use shared libraries, +instructions that call functions or branch to locations in the shared +libraries might show a seemingly bogus location—it’s actually a +location of the relocation table. On some architectures, <small>GDB</small> +might be able to resolve these to actual function names. +</p> +<dl compact="compact"> +<dd><a name="index-set-disassembler_002doptions"></a> +<a name="index-disassembler-options"></a> +</dd> +<dt><code>set disassembler-options <var>option1</var>[,<var>option2</var>…]</code></dt> +<dd><p>This command controls the passing of target specific information to +the disassembler. For a list of valid options, please refer to the +<code>-M</code>/<code>--disassembler-options</code> section of the ‘<samp>objdump</samp>’ +manual and/or the output of <kbd>objdump --help</kbd> +(see <a href="http://sourceware.org/binutils/docs/binutils/objdump.html#objdump">objdump</a> in <cite>The GNU Binary Utilities</cite>). +The default value is the empty string. +</p> +<p>If it is necessary to specify more than one disassembler option, then +multiple options can be placed together into a comma separated list. +Currently this command is only supported on targets ARC, ARM, MIPS, +PowerPC and S/390. +</p> +<a name="index-show-disassembler_002doptions"></a> +</dd> +<dt><code>show disassembler-options</code></dt> +<dd><p>Show the current setting of the disassembler options. +</p></dd> +</dl> + +<dl compact="compact"> +<dd><a name="index-set-disassembly_002dflavor"></a> +<a name="index-Intel-disassembly-flavor"></a> +<a name="index-AT_0026T-disassembly-flavor"></a> +</dd> +<dt><code>set disassembly-flavor <var>instruction-set</var></code></dt> +<dd><p>Select the instruction set to use when disassembling the +program via the <code>disassemble</code> or <code>x/i</code> commands. +</p> +<p>Currently this command is only defined for the Intel x86 family. You +can set <var>instruction-set</var> to either <code>intel</code> or <code>att</code>. +The default is <code>att</code>, the AT&T flavor used by default by Unix +assemblers for x86-based targets. +</p> +<a name="index-show-disassembly_002dflavor"></a> +</dd> +<dt><code>show disassembly-flavor</code></dt> +<dd><p>Show the current setting of the disassembly flavor. +</p></dd> +</dl> + +<dl compact="compact"> +<dd><a name="index-set-disassemble_002dnext_002dline"></a> +<a name="index-show-disassemble_002dnext_002dline"></a> +</dd> +<dt><code>set disassemble-next-line</code></dt> +<dt><code>show disassemble-next-line</code></dt> +<dd><p>Control whether or not <small>GDB</small> will disassemble the next source +line or instruction when execution stops. If ON, <small>GDB</small> will +display disassembly of the next source line when execution of the +program being debugged stops. This is <em>in addition</em> to +displaying the source line itself, which <small>GDB</small> always does if +possible. If the next source line cannot be displayed for some reason +(e.g., if <small>GDB</small> cannot find the source file, or there’s no line +info in the debug info), <small>GDB</small> will display disassembly of the +next <em>instruction</em> instead of showing the next source line. If +AUTO, <small>GDB</small> will display disassembly of next instruction only +if the source line cannot be displayed. This setting causes +<small>GDB</small> to display some feedback when you step through a function +with no line info or whose source file is unavailable. The default is +OFF, which means never display the disassembly of the next line or +instruction. +</p></dd> +</dl> + +<hr> +<div class="header"> +<p> +Next: <a href="Disable-Reading-Source.html#Disable-Reading-Source" accesskey="n" rel="next">Disable Reading Source</a>, Previous: <a href="Source-Path.html#Source-Path" accesskey="p" rel="previous">Source Path</a>, Up: <a href="Source.html#Source" accesskey="u" rel="up">Source</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |