fix incorrect polarity on dyn_offset; closes #364

[ghost]

This fixes #364 and I have verified that --set-interpreter now works correctly on mips64el-linux-gnuabin32.

However --set-rpath is still broken (produces corrupted binaries); fortunately for that task chrpath can be used instead (it works properly).

[Mic92]

cc @iv-m

[Mic92]

So the user of this pointer does dyn->d_un.d_ptr + &dyn->d_un.d_ptr to compute the debug pointer location?

[iv-m]

So the user of this pointer does dyn->d_un.d_ptr + &dyn->d_un.d_ptr to compute the debug pointer location?

I'd say, it's dyn + dyn->d_un.d_ptr. Here is, for example, the relevant part of the glibc's elf loader code (sysdeps/mips/dl-machine.h):

char *ptr = (char *)(l)->l_info[DT_MIPS (RLD_MAP_REL)]; \
ptr += (l)->l_info[DT_MIPS (RLD_MAP_REL)]->d_un.d_val; \

[Mic92]

ping

[iv-m]

cc @iv-m

Sorry for slow reply, I'm checking this out.

[iv-m]

This patch is correct -- I checked on my MIPS32 LE system that with this patch applied, both before and after applying patchelf --set-rpath to a test binary, address of .dynamic section, offset of MIPS_RLD_MAP_REL tag in that section and the contents of MIPS_RLD_MAP_REL add up to __RLD_MAP symbol address, as they should (the numbers taken from readelf).

Apparently I screwed up the signs in #180 and did not notice that: on my mipsel system both + and - for dyn_offset produce working binaries -- all tests of the patchelf test suite pass, gdb works on patched binaries, and suchlike. I'm really sorry for not double checking the math back than.

So, please merge this pull request. @a-m-joseph, thanks for fixing this.

[ghost]

@a-m-joseph, thanks for fixing this.

No problem.

Once this is merged and patchelf makes a release, I would like to upstream all the work I've done on getting nixpkgs to bootstrap on mips64el and mips64el-n32, so it doesn't bitrot.