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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 |
| commit | abdaadbcae30fe0c9a66c7516798279fdfd97750 (patch) | |
| tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/gdb/Separate-Debug-Files.html | |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
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diff --git a/share/doc/gdb/Separate-Debug-Files.html b/share/doc/gdb/Separate-Debug-Files.html new file mode 100644 index 0000000..2e42027 --- /dev/null +++ b/share/doc/gdb/Separate-Debug-Files.html @@ -0,0 +1,357 @@ +<!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: Separate Debug Files</title> + +<meta name="description" content="Debugging with GDB: Separate Debug Files"> +<meta name="keywords" content="Debugging with GDB: Separate Debug Files"> +<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="GDB-Files.html#GDB-Files" rel="up" title="GDB Files"> +<link href="MiniDebugInfo.html#MiniDebugInfo" rel="next" title="MiniDebugInfo"> +<link href="File-Caching.html#File-Caching" rel="previous" title="File Caching"> +<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="Separate-Debug-Files"></a> +<div class="header"> +<p> +Next: <a href="MiniDebugInfo.html#MiniDebugInfo" accesskey="n" rel="next">MiniDebugInfo</a>, Previous: <a href="File-Caching.html#File-Caching" accesskey="p" rel="previous">File Caching</a>, Up: <a href="GDB-Files.html#GDB-Files" accesskey="u" rel="up">GDB Files</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="Debugging-Information-in-Separate-Files"></a> +<h3 class="section">18.3 Debugging Information in Separate Files</h3> +<a name="index-separate-debugging-information-files"></a> +<a name="index-debugging-information-in-separate-files"></a> +<a name="index-_002edebug-subdirectories"></a> +<a name="index-debugging-information-directory_002c-global"></a> +<a name="index-global-debugging-information-directories"></a> +<a name="index-build-ID_002c-and-separate-debugging-files"></a> +<a name="index-_002ebuild_002did-directory"></a> + +<p><small>GDB</small> allows you to put a program’s debugging information in a +file separate from the executable itself, in a way that allows +<small>GDB</small> to find and load the debugging information automatically. +Since debugging information can be very large—sometimes larger +than the executable code itself—some systems distribute debugging +information for their executables in separate files, which users can +install only when they need to debug a problem. +</p> +<p><small>GDB</small> supports two ways of specifying the separate debug info +file: +</p> +<ul> +<li> The executable contains a <em>debug link</em> that specifies the name of +the separate debug info file. The separate debug file’s name is +usually <samp><var>executable</var>.debug</samp>, where <var>executable</var> is the +name of the corresponding executable file without leading directories +(e.g., <samp>ls.debug</samp> for <samp>/usr/bin/ls</samp>). In addition, the +debug link specifies a 32-bit <em>Cyclic Redundancy Check</em> (CRC) +checksum for the debug file, which <small>GDB</small> uses to validate that +the executable and the debug file came from the same build. + +</li><li> <a name="build-ID"></a>The executable contains a <em>build ID</em>, a unique bit string that is +also present in the corresponding debug info file. (This is supported +only on some operating systems, when using the ELF or PE file formats +for binary files and the <small>GNU</small> Binutils.) For more details about +this feature, see the description of the <samp>--build-id</samp> +command-line option in <a href="http://sourceware.org/binutils/docs/ld/Options.html#Options">Command Line Options</a> in <cite>The GNU Linker</cite>. The debug info file’s name is not specified +explicitly by the build ID, but can be computed from the build ID, see +below. +</li></ul> + +<p>Depending on the way the debug info file is specified, <small>GDB</small> +uses two different methods of looking for the debug file: +</p> +<ul> +<li> For the “debug link” method, <small>GDB</small> looks up the named file in +the directory of the executable file, then in a subdirectory of that +directory named <samp>.debug</samp>, and finally under each one of the +global debug directories, in a subdirectory whose name is identical to +the leading directories of the executable’s absolute file name. (On +MS-Windows/MS-DOS, the drive letter of the executable’s leading +directories is converted to a one-letter subdirectory, i.e. +<samp>d:/usr/bin/</samp> is converted to <samp>/d/usr/bin/</samp>, because Windows +filesystems disallow colons in file names.) + +</li><li> For the “build ID” method, <small>GDB</small> looks in the +<samp>.build-id</samp> subdirectory of each one of the global debug directories for +a file named <samp><var>nn</var>/<var>nnnnnnnn</var>.debug</samp>, where <var>nn</var> are the +first 2 hex characters of the build ID bit string, and <var>nnnnnnnn</var> +are the rest of the bit string. (Real build ID strings are 32 or more +hex characters, not 10.) <small>GDB</small> can automatically query +<code>debuginfod</code> servers using build IDs in order to download separate debug +files that cannot be found locally. For more information see <a href="Debuginfod.html#Debuginfod">Debuginfod</a>. +</li></ul> + +<p>So, for example, suppose you ask <small>GDB</small> to debug +<samp>/usr/bin/ls</samp>, which has a debug link that specifies the +file <samp>ls.debug</samp>, and a build ID whose value in hex is +<code>abcdef1234</code>. If the list of the global debug directories includes +<samp>/usr/lib/debug</samp>, then <small>GDB</small> will look for the following +debug information files, in the indicated order: +</p> +<ul class="no-bullet"> +<li>- <samp>/usr/lib/debug/.build-id/ab/cdef1234.debug</samp> +</li><li>- <samp>/usr/bin/ls.debug</samp> +</li><li>- <samp>/usr/bin/.debug/ls.debug</samp> +</li><li>- <samp>/usr/lib/debug/usr/bin/ls.debug</samp>. +</li></ul> + +<p>If the debug file still has not been found and <code>debuginfod</code> +(see <a href="Debuginfod.html#Debuginfod">Debuginfod</a>) is enabled, <small>GDB</small> will attempt to download the +file from <code>debuginfod</code> servers. +</p> +<a name="debug_002dfile_002ddirectory"></a><p>Global debugging info directories default to what is set by <small>GDB</small> +configure option <samp>--with-separate-debug-dir</samp>. During <small>GDB</small> run +you can also set the global debugging info directories, and view the list +<small>GDB</small> is currently using. +</p> +<dl compact="compact"> +<dd> +<a name="index-set-debug_002dfile_002ddirectory"></a> +</dd> +<dt><code>set debug-file-directory <var>directories</var></code></dt> +<dd><p>Set the directories which <small>GDB</small> searches for separate debugging +information files to <var>directory</var>. Multiple path components can be set +concatenating them by a path separator. +</p> +<a name="index-show-debug_002dfile_002ddirectory"></a> +</dd> +<dt><code>show debug-file-directory</code></dt> +<dd><p>Show the directories <small>GDB</small> searches for separate debugging +information files. +</p> +</dd> +</dl> + +<a name="index-_002egnu_005fdebuglink-sections"></a> +<a name="index-debug-link-sections"></a> +<p>A debug link is a special section of the executable file named +<code>.gnu_debuglink</code>. The section must contain: +</p> +<ul> +<li> A filename, with any leading directory components removed, followed by +a zero byte, +</li><li> zero to three bytes of padding, as needed to reach the next four-byte +boundary within the section, and +</li><li> a four-byte CRC checksum, stored in the same endianness used for the +executable file itself. The checksum is computed on the debugging +information file’s full contents by the function given below, passing +zero as the <var>crc</var> argument. +</li></ul> + +<p>Any executable file format can carry a debug link, as long as it can +contain a section named <code>.gnu_debuglink</code> with the contents +described above. +</p> +<a name="index-_002enote_002egnu_002ebuild_002did-sections"></a> +<a name="index-build-ID-sections"></a> +<p>The build ID is a special section in the executable file (and in other +ELF binary files that <small>GDB</small> may consider). This section is +often named <code>.note.gnu.build-id</code>, but that name is not mandatory. +It contains unique identification for the built files—the ID remains +the same across multiple builds of the same build tree. The default +algorithm SHA1 produces 160 bits (40 hexadecimal characters) of the +content for the build ID string. The same section with an identical +value is present in the original built binary with symbols, in its +stripped variant, and in the separate debugging information file. +</p> +<p>The debugging information file itself should be an ordinary +executable, containing a full set of linker symbols, sections, and +debugging information. The sections of the debugging information file +should have the same names, addresses, and sizes as the original file, +but they need not contain any data—much like a <code>.bss</code> section +in an ordinary executable. +</p> +<p>The <small>GNU</small> binary utilities (Binutils) package includes the +‘<samp>objcopy</samp>’ utility that can produce +the separated executable / debugging information file pairs using the +following commands: +</p> +<div class="smallexample"> +<pre class="smallexample"><kbd>objcopy --only-keep-debug foo foo.debug</kbd> +<kbd>strip -g foo</kbd> +</pre></div> + +<p>These commands remove the debugging +information from the executable file <samp>foo</samp> and place it in the file +<samp>foo.debug</samp>. You can use the first, second or both methods to link the +two files: +</p> +<ul> +<li> The debug link method needs the following additional command to also leave +behind a debug link in <samp>foo</samp>: + +<div class="smallexample"> +<pre class="smallexample"><kbd>objcopy --add-gnu-debuglink=foo.debug foo</kbd> +</pre></div> + +<p>Ulrich Drepper’s <samp>elfutils</samp> package, starting with version 0.53, contains +a version of the <code>strip</code> command such that the command <kbd>strip foo -f +foo.debug</kbd> has the same functionality as the two <code>objcopy</code> commands and +the <code>ln -s</code> command above, together. +</p> +</li><li> Build ID gets embedded into the main executable using <code>ld --build-id</code> or +the <small>GCC</small> counterpart <code>gcc -Wl,--build-id</code>. Build ID support plus +compatibility fixes for debug files separation are present in <small>GNU</small> binary +utilities (Binutils) package since version 2.18. +</li></ul> + + +<a name="index-CRC-algorithm-definition"></a> +<p>The CRC used in <code>.gnu_debuglink</code> is the CRC-32 defined in +IEEE 802.3 using the polynomial: +</p> +<div class="display"> +<pre class="display"> <em>x</em><sup>32</sup> + <em>x</em><sup>26</sup> + <em>x</em><sup>23</sup> + <em>x</em><sup>22</sup> + <em>x</em><sup>16</sup> + <em>x</em><sup>12</sup> + <em>x</em><sup>11</sup> + + <em>x</em><sup>10</sup> + <em>x</em><sup>8</sup> + <em>x</em><sup>7</sup> + <em>x</em><sup>5</sup> + <em>x</em><sup>4</sup> + <em>x</em><sup>2</sup> + <em>x</em> + 1</pre></div> + +<p>The function is computed byte at a time, taking the least +significant bit of each byte first. The initial pattern +<code>0xffffffff</code> is used, to ensure leading zeros affect the CRC and +the final result is inverted to ensure trailing zeros also affect the +CRC. +</p> +<p><em>Note:</em> This is the same CRC polynomial as used in handling the +<em>Remote Serial Protocol</em> <code>qCRC</code> packet (see <a href="General-Query-Packets.html#qCRC-packet">qCRC packet</a>). +However in the case of the Remote Serial Protocol, the CRC is computed +<em>most</em> significant bit first, and the result is not inverted, so +trailing zeros have no effect on the CRC value. +</p> +<p>To complete the description, we show below the code of the function +which produces the CRC used in <code>.gnu_debuglink</code>. Inverting the +initially supplied <code>crc</code> argument means that an initial call to +this function passing in zero will start computing the CRC using +<code>0xffffffff</code>. +</p> +<a name="index-gnu_005fdebuglink_005fcrc32"></a> +<div class="smallexample"> +<pre class="smallexample">unsigned long +gnu_debuglink_crc32 (unsigned long crc, + unsigned char *buf, size_t len) +{ + static const unsigned long crc32_table[256] = + { + 0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, + 0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, + 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, + 0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de, + 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856, + 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9, + 0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, + 0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, + 0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, + 0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a, + 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599, + 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924, + 0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, + 0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, + 0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e, + 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01, + 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed, + 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950, + 0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, + 0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, + 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, + 0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5, + 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010, + 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f, + 0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, + 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, + 0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615, + 0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8, + 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344, + 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb, + 0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, + 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, + 0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, + 0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c, + 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef, + 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236, + 0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, + 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, + 0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c, + 0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713, + 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b, + 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242, + 0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, + 0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, + 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278, + 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7, + 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66, + 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9, + 0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, + 0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, + 0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, + 0x2d02ef8d + }; + unsigned char *end; + + crc = ~crc & 0xffffffff; + for (end = buf + len; buf < end; ++buf) + crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8); + return ~crc & 0xffffffff; +} +</pre></div> + +<p>This computation does not apply to the “build ID” method. +</p> +<hr> +<div class="header"> +<p> +Next: <a href="MiniDebugInfo.html#MiniDebugInfo" accesskey="n" rel="next">MiniDebugInfo</a>, Previous: <a href="File-Caching.html#File-Caching" accesskey="p" rel="previous">File Caching</a>, Up: <a href="GDB-Files.html#GDB-Files" accesskey="u" rel="up">GDB Files</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> |