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diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo index 77360d0..af85889 100644 --- a/gdb/doc/gdb.texinfo +++ b/gdb/doc/gdb.texinfo @@ -9342,6 +9342,7 @@ program. To debug a core dump of a previous run, you must also tell @menu * Files:: Commands to specify files +* Separate Debug Files:: Debugging information in separate files * Symbol Errors:: Errors reading symbol files @end menu @@ -9789,6 +9790,190 @@ set @samp{solib-absolute-prefix} to a nonexistant directory to prevent Display the current shared library search path. @end table + +@node Separate Debug Files +@section Debugging Information in Separate Files +@cindex separate debugging information files +@cindex debugging information in separate files +@cindex @file{.debug} subdirectories +@cindex debugging information directory, global +@cindex global debugging information directory + +@value{GDBN} allows you to put a program's debugging information in a +file separate from the executable itself, in a way that allows +@value{GDBN} 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. + +If an executable's debugging information has been extracted to a +separate file, the executable should contain a @dfn{debug link} giving +the name of the debugging information file (with no directory +components), and a checksum of its contents. (The exact form of a +debug link is described below.) If the full name of the directory +containing the executable is @var{execdir}, and the executable has a +debug link that specifies the name @var{debugfile}, then @value{GDBN} +will automatically search for the debugging information file in three +places: + +@itemize @bullet +@item +the directory containing the executable file (that is, it will look +for a file named @file{@var{execdir}/@var{debugfile}}, +@item +a subdirectory of that directory named @file{.debug} (that is, the +file @file{@var{execdir}/.debug/@var{debugfile}}, and +@item +a subdirectory of the global debug file directory that includes the +executable's full path, and the name from the link (that is, the file +@file{@var{globaldebugdir}/@var{execdir}/@var{debugfile}}, where +@var{globaldebugdir} is the global debug file directory, and +@var{execdir} has been turned into a relative path). +@end itemize +@noindent +@value{GDBN} checks under each of these names for a debugging +information file whose checksum matches that given in the link, and +reads the debugging information from the first one it finds. + +So, for example, if you ask @value{GDBN} to debug @file{/usr/bin/ls}, +which has a link containing the name @file{ls.debug}, and the global +debug directory is @file{/usr/lib/debug}, then @value{GDBN} will look +for debug information in @file{/usr/bin/ls.debug}, +@file{/usr/bin/.debug/ls.debug}, and +@file{/usr/lib/debug/usr/bin/ls.debug}. + +You can set the global debugging info directory's name, and view the +name @value{GDBN} is currently using. + +@table @code + +@kindex set debug-file-directory +@item set debug-file-directory @var{directory} +Set the directory which @value{GDBN} searches for separate debugging +information files to @var{directory}. + +@kindex show debug-file-directory +@item show debug-file-directory +Show the directory @value{GDBN} searches for separate debugging +information files. + +@end table + +@cindex @code{.gnu_debuglink} sections +@cindex debug links +A debug link is a special section of the executable file named +@code{.gnu_debuglink}. The section must contain: + +@itemize +@item +A filename, with any leading directory components removed, followed by +a zero byte, +@item +zero to three bytes of padding, as needed to reach the next four-byte +boundary within the section, and +@item +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} argument. +@end itemize + +Any executable file format can carry a debug link, as long as it can +contain a section named @code{.gnu_debuglink} with the contents +described above. + +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} section +in an ordinary executable. + +As of December 2002, there is no standard GNU utility to produce +separated executable / debugging information file pairs. Ulrich +Drepper's @file{elfutils} package, starting with version 0.53, +contains a version of the @code{strip} command such that the command +@kbd{strip foo -f foo.debug} removes the debugging information from +the executable file @file{foo}, places it in the file +@file{foo.debug}, and leaves behind a debug link in @file{foo}. + +Since there are many different ways to compute CRC's (different +polynomials, reversals, byte ordering, etc.), the simplest way to +describe the CRC used in @code{.gnu_debuglink} sections is to give the +complete code for a function that computes it: + +@kindex @code{gnu_debuglink_crc32} +@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;; +@} +@end smallexample + + @node Symbol Errors @section Errors reading symbol files |