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Document /proc/self/exe and workaround.

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John Reiser
2006-09-25 13:02:07 -07:00
parent 6a5bee0cdd
commit 53ca41717a
1 changed files with 12 additions and 1 deletions
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doc/elf-to-mem.txt
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@@ -17,7 +17,7 @@ program itself. So, the decompressor program (which contains the
compressed version of the original executable) must have the same compressed version of the original executable) must have the same
brk() as the original executable. So, the second PT_LOAD brk() as the original executable. So, the second PT_LOAD
ELF "segment" of the compressed program is used only to set the brk(0). ELF "segment" of the compressed program is used only to set the brk(0).
See src/p_lx_elf.cpp, function PackLinuxI386elf::patchLoader(). See src/p_lx_elf.cpp, function PackLinuxElf32::generateElfHdr.
All of the decompressor's code, and all of the compressed image All of the decompressor's code, and all of the compressed image
of the original executable, reside in the first PT_LOAD of the of the original executable, reside in the first PT_LOAD of the
decompressor program. decompressor program.
@@ -63,3 +63,14 @@ clear the free portion of the stack (to compensate for ld-linux.so.2
assuming that its automatic stack variables are initialized to zero), assuming that its automatic stack variables are initialized to zero),
and remove (all but 4 bytes of) the decompression program (and and remove (all but 4 bytes of) the decompression program (and
compressed executable) from the address space. compressed executable) from the address space.
Because the UPX runtime stub removes all traces of the compressed file
from the address space, then the Linux kernel erases the symlink
/proc/self/exe. Linux stores the pathname argument that was specified
to execve() immediately after the '\0' which terminates the character
string of the last environment variable [as of execve()]. This is true
for at least all Linux 2.6, 2.4, and 2.2 kernels. The pathname is not
"bound" to the file as strongly as /proc/self/exe (the file may be changed
without affecting the pathname), but the pathname does provide some
information. The pathname may be relative to the working directory,
so look before any chdir().