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Document /proc/self/exe problems on arm*-linux-elf.

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John Reiser 2011-12-13 10:53:26 -08:00
parent 67f7e0089c
commit c56eefc739
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doc/elf-to-mem.txt
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@ -76,6 +76,21 @@ and previous versions did this by default with no option. However,
too much other software erroneously assumes that /proc/self/exe
always exists.
On arm*-linux-elf there is no good address at which to retain one
page of the compressed executable. Pages below the usual .p_vaddr
0x8000 (32KiB) are rejected by the kernel. Using a page above the
original uncompressed brk(0) would require placing the entire initial
compressed program above uncompressed brk(0), which would significantly
increase the running brk(0); but too many programs break if brk(0)
moves. Thus on arm*-linux-elf the compressed executable begins
with 0x8000==.p_vaddr, all pages mapped by execve() that are also
occupied by decompressed bytes are removed before overwriting, and
/proc/self/exe becomes a "(deleted)" symlink. It might be possible
to preserve /proc/self/exe if the original uncompressed executable
were created with 0x9000==.p_vaddr (one page higher than the usual
0x8000) so that the compressed page mapped at 0x8000 would linger.
[This has not been tested.]
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