InLinux, theSystem.map file is asymbol table used by thekernel.
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 debuggingkernel panics andkernel oopses. The kernel does the address-to-name translation itself whenCONFIG_KALLSYMS is enabled so that tools like ksymoops are not required.[1]
The following is part of aSystem.map file:[2]
c041bc90 b packet_sklistc041bc94 b packet_sklist_lockc041bc94 b packet_socks_nrc041bc98 A __bss_stopc041bc98 A _endc041c000 A pg0ffffe400 A __kernel_vsyscallffffe410 A SYSENTER_RETURNffffe420 A __kernel_sigreturnffffe440 A __kernel_rt_sigreturn
Because addresses may change from one build to the next, a newSystem.map is generated for each build of the kernel.[3]
The character between the address and the symbol (separated by spaces) is thetype of a symbol. Thenm utility program onUnix systems lists the symbols from object files. TheSystem.map is directly related to it, in that this file is produced bynm on the whole kernel program – just likenm lists the symbols and their types for any small object programs.[4]
Some of these types are:[4]
A for absoluteB orb for uninitialized data section (called BSS)D ord for initialized data sectionG org for initialized data section for small objects (global)i for sections specific to DLLsN for debugging symbolp for stack unwind sectionR orr for read only data sectionS ors for uninitialized data section for small objectsT ort for text (code) sectionU for undefinedV orv for weak objectW orw for weak objects which have not been tagged so- for stabs symbol in an a.out object file? for "symbol type unknown"After building theLinux kernel,System.map is located in the root of the source directory. However, some further software installation steps expect to locate the file elsewhere:[5]
/boot/System.map-$(uname -r)/lib/modules/$(uname -r)/build/System.map| Linux kernel | |
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