On 16 Dec 2013 16:37, "Michael Hudson-Doyle" <michael.hud...@linaro.org> wrote: > > Michael Hudson-Doyle <michael.hud...@linaro.org> writes: > > > Aaah, you might be onto something there. I built myself a cross gcc-4.8 > > today and it appeared to compile things correctly (I didn't actually get > > to run it, but the objdump poking looked right) and I got a bit worried > > that this was all down to some cosmic ray / corruption when I first > > compiled it. But, the scripts I cargo culted just use compile binutils > > from git tip, so if the bug is in binutils... > > So I still don't know what's going on, exactly, but I have a debug build > of binutils now and some clues. It still only happens on real hardware, > not cross compiling on my laptop, but I think I have an idea as to why. > This might be complete crack, but anyway. > > I think it's to do with the order of things within the GOT. > > When I cross compile, sort the relocations by address, then count up the > number of relocations of each type, it looks like this: > > $ objdump -C -R build/linux2/*/mongo/base/counter_test | LC_ALL=C sort | cut -d' ' -f 2 | uniq -c > 4 > 496 R_AARCH64_GLOB_DAT > 1 R_AARCH64_TLS_TPREL64 > 103 R_AARCH64_GLOB_DAT > 305 R_AARCH64_JUMP_SLOT > 12 R_AARCH64_COPY > 1 RELOCATION > 2 > > In this case, the code and the relocation agree on where the thread > local variable is. > > When I compile natively, it looks like this: > > (t-mwhudson)ubuntu@arm64:~/src/mongo$ objdump -C -R build/linux2/*/mongo/base/counter_test | LC_ALL=C sort | cut -d' ' -f 2 | uniq -c > 4 > 295 R_AARCH64_JUMP_SLOT > 496 R_AARCH64_GLOB_DAT > 1 R_AARCH64_TLS_TPREL64 > 104 R_AARCH64_GLOB_DAT > 12 R_AARCH64_COPY > 1 RELOCATION > 2 > > And the code and the relocation disagree on where the thread local > variable is -- by 298 * sizeof(void*). Which is almost (but I admit, > not exactly) the number of JUMP_SLOTs that are, in this case, before the > TLS variable in the GOT. When I compiled in a different way, there were > only 160 JUMP_SLOTs before the TLS reloc, and the code and relocation > disagreed by 163 slots. > > So is it possible somehow that the GOT has these JUMP_SLOTs inserted > into it after the relocation for the TLS has been written out?
I guess I really mean "between patching the code and writing the relocs out" here. > I don't > really see how but maybe this rings a bell... > > Cheers, > mwh > > _______________________________________________ > linaro-toolchain mailing list > linaro-toolchain@lists.linaro.org > http://lists.linaro.org/mailman/listinfo/linaro-toolchain
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