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diff --git a/share/doc/gdb/Memory.html b/share/doc/gdb/Memory.html new file mode 100644 index 0000000..9aa8be3 --- /dev/null +++ b/share/doc/gdb/Memory.html @@ -0,0 +1,283 @@ +<!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: Memory</title> + +<meta name="description" content="Debugging with GDB: Memory"> +<meta name="keywords" content="Debugging with GDB: Memory"> +<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="Data.html#Data" rel="up" title="Data"> +<link href="Memory-Tagging.html#Memory-Tagging" rel="next" title="Memory Tagging"> +<link href="Output-Formats.html#Output-Formats" rel="previous" title="Output Formats"> +<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="Memory"></a> +<div class="header"> +<p> +Next: <a href="Memory-Tagging.html#Memory-Tagging" accesskey="n" rel="next">Memory Tagging</a>, Previous: <a href="Output-Formats.html#Output-Formats" accesskey="p" rel="previous">Output Formats</a>, Up: <a href="Data.html#Data" accesskey="u" rel="up">Data</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="Examining-Memory"></a> +<h3 class="section">10.6 Examining Memory</h3> + +<p>You can use the command <code>x</code> (for “examine”) to examine memory in +any of several formats, independently of your program’s data types. +</p> +<a name="index-examining-memory"></a> +<dl compact="compact"> +<dd><a name="index-x-_0028examine-memory_0029"></a> +</dd> +<dt><code>x/<var>nfu</var> <var>addr</var></code></dt> +<dt><code>x <var>addr</var></code></dt> +<dt><code>x</code></dt> +<dd><p>Use the <code>x</code> command to examine memory. +</p></dd> +</dl> + +<p><var>n</var>, <var>f</var>, and <var>u</var> are all optional parameters that specify how +much memory to display and how to format it; <var>addr</var> is an +expression giving the address where you want to start displaying memory. +If you use defaults for <var>nfu</var>, you need not type the slash ‘<samp>/</samp>’. +Several commands set convenient defaults for <var>addr</var>. +</p> +<dl compact="compact"> +<dt><span class="roman"><var>n</var>, the repeat count</span></dt> +<dd><p>The repeat count is a decimal integer; the default is 1. It specifies +how much memory (counting by units <var>u</var>) to display. If a negative +number is specified, memory is examined backward from <var>addr</var>. +</p> +</dd> +<dt><span class="roman"><var>f</var>, the display format</span></dt> +<dd><p>The display format is one of the formats used by <code>print</code> +(‘<samp>x</samp>’, ‘<samp>d</samp>’, ‘<samp>u</samp>’, ‘<samp>o</samp>’, ‘<samp>t</samp>’, ‘<samp>a</samp>’, ‘<samp>c</samp>’, +‘<samp>f</samp>’, ‘<samp>s</samp>’), ‘<samp>i</samp>’ (for machine instructions) and +‘<samp>m</samp>’ (for displaying memory tags). +The default is ‘<samp>x</samp>’ (hexadecimal) initially. The default changes +each time you use either <code>x</code> or <code>print</code>. +</p> +</dd> +<dt><span class="roman"><var>u</var>, the unit size</span></dt> +<dd><p>The unit size is any of +</p> +<dl compact="compact"> +<dt><code>b</code></dt> +<dd><p>Bytes. +</p></dd> +<dt><code>h</code></dt> +<dd><p>Halfwords (two bytes). +</p></dd> +<dt><code>w</code></dt> +<dd><p>Words (four bytes). This is the initial default. +</p></dd> +<dt><code>g</code></dt> +<dd><p>Giant words (eight bytes). +</p></dd> +</dl> + +<p>Each time you specify a unit size with <code>x</code>, that size becomes the +default unit the next time you use <code>x</code>. For the ‘<samp>i</samp>’ format, +the unit size is ignored and is normally not written. For the ‘<samp>s</samp>’ format, +the unit size defaults to ‘<samp>b</samp>’, unless it is explicitly given. +Use <kbd>x /hs</kbd> to display 16-bit char strings and <kbd>x /ws</kbd> to display +32-bit strings. The next use of <kbd>x /s</kbd> will again display 8-bit strings. +Note that the results depend on the programming language of the +current compilation unit. If the language is C, the ‘<samp>s</samp>’ +modifier will use the UTF-16 encoding while ‘<samp>w</samp>’ will use +UTF-32. The encoding is set by the programming language and cannot +be altered. +</p> +</dd> +<dt><span class="roman"><var>addr</var>, starting display address</span></dt> +<dd><p><var>addr</var> is the address where you want <small>GDB</small> to begin displaying +memory. The expression need not have a pointer value (though it may); +it is always interpreted as an integer address of a byte of memory. +See <a href="Expressions.html#Expressions">Expressions</a>, for more information on expressions. The default for +<var>addr</var> is usually just after the last address examined—but several +other commands also set the default address: <code>info breakpoints</code> (to +the address of the last breakpoint listed), <code>info line</code> (to the +starting address of a line), and <code>print</code> (if you use it to display +a value from memory). +</p></dd> +</dl> + +<p>For example, ‘<samp>x/3uh 0x54320</samp>’ is a request to display three halfwords +(<code>h</code>) of memory, formatted as unsigned decimal integers (‘<samp>u</samp>’), +starting at address <code>0x54320</code>. ‘<samp>x/4xw $sp</samp>’ prints the four +words (‘<samp>w</samp>’) of memory above the stack pointer (here, ‘<samp>$sp</samp>’; +see <a href="Registers.html#Registers">Registers</a>) in hexadecimal (‘<samp>x</samp>’). +</p> +<p>You can also specify a negative repeat count to examine memory backward +from the given address. For example, ‘<samp>x/-3uh 0x54320</samp>’ prints three +halfwords (<code>h</code>) at <code>0x5431a</code>, <code>0x5431c</code>, and <code>0x5431e</code>. +</p> +<p>Since the letters indicating unit sizes are all distinct from the +letters specifying output formats, you do not have to remember whether +unit size or format comes first; either order works. The output +specifications ‘<samp>4xw</samp>’ and ‘<samp>4wx</samp>’ mean exactly the same thing. +(However, the count <var>n</var> must come first; ‘<samp>wx4</samp>’ does not work.) +</p> +<p>Even though the unit size <var>u</var> is ignored for the formats ‘<samp>s</samp>’ +and ‘<samp>i</samp>’, you might still want to use a count <var>n</var>; for example, +‘<samp>3i</samp>’ specifies that you want to see three machine instructions, +including any operands. For convenience, especially when used with +the <code>display</code> command, the ‘<samp>i</samp>’ format also prints branch delay +slot instructions, if any, beyond the count specified, which immediately +follow the last instruction that is within the count. The command +<code>disassemble</code> gives an alternative way of inspecting machine +instructions; see <a href="Machine-Code.html#Machine-Code">Source and Machine Code</a>. +</p> +<p>If a negative repeat count is specified for the formats ‘<samp>s</samp>’ or ‘<samp>i</samp>’, +the command displays null-terminated strings or instructions before the given +address as many as the absolute value of the given number. For the ‘<samp>i</samp>’ +format, we use line number information in the debug info to accurately locate +instruction boundaries while disassembling backward. If line info is not +available, the command stops examining memory with an error message. +</p> +<p>All the defaults for the arguments to <code>x</code> are designed to make it +easy to continue scanning memory with minimal specifications each time +you use <code>x</code>. For example, after you have inspected three machine +instructions with ‘<samp>x/3i <var>addr</var></samp>’, you can inspect the next seven +with just ‘<samp>x/7</samp>’. If you use <tt class="key">RET</tt> to repeat the <code>x</code> command, +the repeat count <var>n</var> is used again; the other arguments default as +for successive uses of <code>x</code>. +</p> +<p>When examining machine instructions, the instruction at current program +counter is shown with a <code>=></code> marker. For example: +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) x/5i $pc-6 + 0x804837f <main+11>: mov %esp,%ebp + 0x8048381 <main+13>: push %ecx + 0x8048382 <main+14>: sub $0x4,%esp +=> 0x8048385 <main+17>: movl $0x8048460,(%esp) + 0x804838c <main+24>: call 0x80482d4 <puts@plt> +</pre></div> + +<p>If the architecture supports memory tagging, the tags can be displayed by +using ‘<samp>m</samp>’. See <a href="Memory-Tagging.html#Memory-Tagging">Memory Tagging</a>. +</p> +<p>The information will be displayed once per granule size +(the amount of bytes a particular memory tag covers). For example, AArch64 +has a granule size of 16 bytes, so it will display a tag every 16 bytes. +</p> +<p>Due to the way <small>GDB</small> prints information with the <code>x</code> command (not +aligned to a particular boundary), the tag information will refer to the +initial address displayed on a particular line. If a memory tag boundary +is crossed in the middle of a line displayed by the <code>x</code> command, it +will be displayed on the next line. +</p> +<p>The ‘<samp>m</samp>’ format doesn’t affect any other specified formats that were +passed to the <code>x</code> command. +</p> +<a name="index-_0024_005f_002c-_0024_005f_005f_002c-and-value-history"></a> +<p>The addresses and contents printed by the <code>x</code> command are not saved +in the value history because there is often too much of them and they +would get in the way. Instead, <small>GDB</small> makes these values available for +subsequent use in expressions as values of the convenience variables +<code>$_</code> and <code>$__</code>. After an <code>x</code> command, the last address +examined is available for use in expressions in the convenience variable +<code>$_</code>. The contents of that address, as examined, are available in +the convenience variable <code>$__</code>. +</p> +<p>If the <code>x</code> command has a repeat count, the address and contents saved +are from the last memory unit printed; this is not the same as the last +address printed if several units were printed on the last line of output. +</p> +<a name="addressable-memory-unit"></a><a name="index-addressable-memory-unit"></a> +<p>Most targets have an addressable memory unit size of 8 bits. This means +that to each memory address are associated 8 bits of data. Some +targets, however, have other addressable memory unit sizes. +Within <small>GDB</small> and this document, the term +<em>addressable memory unit</em> (or <em>memory unit</em> for short) is used +when explicitly referring to a chunk of data of that size. The word +<em>byte</em> is used to refer to a chunk of data of 8 bits, regardless of +the addressable memory unit size of the target. For most systems, +addressable memory unit is a synonym of byte. +</p> +<a name="index-remote-memory-comparison"></a> +<a name="index-target-memory-comparison"></a> +<a name="index-verify-remote-memory-image"></a> +<a name="index-verify-target-memory-image"></a> +<p>When you are debugging a program running on a remote target machine +(see <a href="Remote-Debugging.html#Remote-Debugging">Remote Debugging</a>), you may wish to verify the program’s image +in the remote machine’s memory against the executable file you +downloaded to the target. Or, on any target, you may want to check +whether the program has corrupted its own read-only sections. The +<code>compare-sections</code> command is provided for such situations. +</p> +<dl compact="compact"> +<dd><a name="index-compare_002dsections"></a> +</dd> +<dt><code>compare-sections <span class="roman">[</span><var>section-name</var><span class="roman">|</span><code>-r</code><span class="roman">]</span></code></dt> +<dd><p>Compare the data of a loadable section <var>section-name</var> in the +executable file of the program being debugged with the same section in +the target machine’s memory, and report any mismatches. With no +arguments, compares all loadable sections. With an argument of +<code>-r</code>, compares all loadable read-only sections. +</p> +<p>Note: for remote targets, this command can be accelerated if the +target supports computing the CRC checksum of a block of memory +(see <a href="General-Query-Packets.html#qCRC-packet">qCRC packet</a>). +</p></dd> +</dl> + +<hr> +<div class="header"> +<p> +Next: <a href="Memory-Tagging.html#Memory-Tagging" accesskey="n" rel="next">Memory Tagging</a>, Previous: <a href="Output-Formats.html#Output-Formats" accesskey="p" rel="previous">Output Formats</a>, Up: <a href="Data.html#Data" accesskey="u" rel="up">Data</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> |