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<p><b>New page</b></p><div>{{Short description|Symbol table used by the Linux kernel}}<br />
In [[Linux]], the {{mono|'''System.map'''}} file is a [[symbol table]] used by the [[kernel (operating system)|kernel]].<br />
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A symbol table is a look-up between symbol names and their addresses in memory. A symbol name may be the name of a variable or the name of a function. The System.map is required when the address of a symbol name, or the symbol name of an address, is needed. It is especially useful for debugging [[kernel panic]]s and [[Linux kernel oops|kernel oops]]es. The kernel does the address-to-name translation itself when <code>CONFIG_KALLSYMS</code> is enabled so that tools like ksymoops are not required.<ref>{{cite web|url=https://kernelnewbies.org/FAQ/System.map |title=FAQ/System.map - Linux Kernel Newbies |publisher=kernelnewbies.org |date=2006-04-14 |access-date=2014-04-06}}</ref><br />
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==Internals==<br />
The following is part of a <code>System.map</code> file:<ref>{{cite web|author=Peter Jay Salzman |url=https://rlworkman.net/system.map/ |title=The system.map File |publisher=Rlworkman.net |date=2003-05-28 |access-date=2014-04-06}}</ref><br />
<syntaxhighlight lang="asm"><br />
c041bc90 b packet_sklist<br />
c041bc94 b packet_sklist_lock<br />
c041bc94 b packet_socks_nr<br />
c041bc98 A __bss_stop<br />
c041bc98 A _end<br />
c041c000 A pg0<br />
ffffe400 A __kernel_vsyscall<br />
ffffe410 A SYSENTER_RETURN<br />
ffffe420 A __kernel_sigreturn<br />
ffffe440 A __kernel_rt_sigreturn<br />
</syntaxhighlight><br />
Because addresses may change from one build to the next, a new <code>System.map</code> is generated for each build of the kernel.<ref>{{cite web|url=http://www.faqs.org/docs/Linux-HOWTO/Kernel-HOWTO.html#systemmap |title=Kernel-HOWTO |publisher=faqs.org |access-date=2014-04-06}}</ref><br />
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===Symbol types===<br />
The character between the address and the symbol (separated by spaces) is the ''type'' of a symbol. The <code>[[nm (Unix)|nm]]</code> utility program on [[Unix system]]s lists the symbols from object files. The <code>System.map</code> is directly related to it, in that this file is produced by <code>nm</code> on the whole kernel program{{snd}} just like <code>nm</code> lists the symbols and their types for any small object programs.<ref name="nm-man">{{cite web|url=https://linux.die.net/man/1/nm |title=nm(1): symbols from object files - Linux man page |publisher=Linux.die.net |access-date=2014-04-06}}</ref><br />
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Some of these types are:<ref name="nm-man" /><br />
{{Div col|colwidth=30em}}<br />
* <code>A</code> for absolute<br />
* <code>B</code> or <code>b</code> for uninitialized data section (called BSS)<br />
* <code>D</code> or <code>d</code> for initialized data section<br />
* <code>G</code> or <code>g</code> for initialized data section for small objects (global)<br />
* <code>i</code> for sections specific to DLLs<br />
* <code>N</code> for debugging symbol<br />
* <code>p</code> for stack unwind section<br />
* <code>R</code> or <code>r</code> for read only data section<br />
* <code>S</code> or <code>s</code> for uninitialized data section for small objects<br />
* <code>T</code> or <code>t</code> for text (code) section<br />
* <code>U</code> for undefined<br />
* <code>V</code> or <code>v</code> for weak object<br />
* <code>W</code> or <code>w</code> for weak objects which have not been tagged so<br />
* <code>-</code> for stabs symbol in an a.out object file<br />
* <code>?</code> for "symbol type unknown"<br />
{{Div col end}}<br />
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==Filesystem location==<br />
After building the [[Linux kernel]], <code>System.map</code> is located in the root of the source directory. However, some further software installation steps expect to locate the file elsewhere:<ref>{{cite web|url=http://linuxmafia.com/faq/Kernel/systemmap.html |title=Peter's Notes: System.map |publisher=Linuxmafia.com |date=2003-05-29 |access-date=2014-04-06}}</ref><br />
* as <code>[[/boot/]]System.map-$([[uname]] -r)</code><br />
* building [[SVGALib|SVGAlib]] expects to find <code>/lib/modules/$(uname -r)/build/System.map</code><br />
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==See also==<br />
{{Portal|Linux}}<br />
* [[Linux kernel oops]]<br />
* [[Kernel panic]]<br />
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==References==<br />
{{Reflist}}<br />
<br />
{{Linux}}<br />
{{Linux kernel}}<br />
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[[Category:Executable file formats]]<br />
[[Category:Linux kernel]]</div>imported>Frap