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Diffstat (limited to 'externals/breakpad/docs/linux_system_calls.md')
| -rw-r--r-- | externals/breakpad/docs/linux_system_calls.md | 47 |
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diff --git a/externals/breakpad/docs/linux_system_calls.md b/externals/breakpad/docs/linux_system_calls.md deleted file mode 100644 index 17ada7e036..0000000000 --- a/externals/breakpad/docs/linux_system_calls.md +++ /dev/null @@ -1,47 +0,0 @@ -# Introduction - -Linux implements its userland-to-kernel transition using a special library -called linux-gate.so that is mapped by the kernel into every process. For more -information, see - -http://www.trilithium.com/johan/2005/08/linux-gate/ - -In a nutshell, the problem is that the system call gate function, -kernel\_vsyscall does not use EBP to point to the frame pointer. - -However, the Breakpad processor supports special frames like this via STACK -lines in the symbol file. If you look in src/client/linux/data you will see -symbol files for linux-gate.so for both Intel & AMD(the implementation of -kernel\_vsyscall changes depending on the CPU manufacturer). When processing -minidumps from Linux 2.6, having these symbol files is necessary for walking the -stack for crashes that happen while a thread is in a system call. - -If you're just interested in processing minidumps, those two symbol files should -be all you need! - -# Details - -The particular details of understanding the linux-gate.so symbol files can be -found by reading about STACK lines inside -src/common/windows/pdb\_source\_line\_writer.cc, and the above link. To -summarize briefly, we just have to inform the processor how to get to the -previous frame when the EIP is inside kernel\_vsyscall, and we do that by -telling the processor how many bytes kernel\_vsyscall has pushed onto the stack -in it's prologue. For example, one of the symbol files looks somewhat like the -following: - -MODULE Linux x86 random\_debug\_id linux-gate.so PUBLIC 400 0 kernel\_vsyscall -STACK WIN 4 100 1 1 0 0 0 0 0 1 - -The PUBLIC line indicates that kernel\_vsyscall is at offset 400 (in bytes) from -the beginning of linux-gate.so. The STACK line indicates the size of the -function(100), how many bytes it pushes(1), and how many bytes it pops(1). The -last 1 indicates that EBP is pushed onto the stack before being used by the -function. - -# Warnings - -These functions might change significantly depending on kernel version. In my -opinion, the actual function stack information is unlikely to change frequently, -but the Linux kernel might change the address of kernel\_vsyscall w.r.t the -beginning of linux-gate.so, which would cause these symbol files to be invalid. |