[lld] r270346 - Simplify SplitInputSection::getRangeAndSize.

[Rui Ueyama via llvm-commits]

So it is a special case that .eh_frame contains only the terminator (empty)
record and there is a relocation pointing to offset 0 of .eh_frame, correct?

On Tue, May 24, 2016 at 3:10 AM, Simon Atanasyan <simon at atanasyan.com>
wrote:

> Hi,
>
> On Sun, May 22, 2016 at 3:41 AM, Rui Ueyama via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
> > Author: ruiu
> > Date: Sat May 21 19:41:38 2016
> > New Revision: 270346
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=270346&view=rev
> > Log:
> > Simplify SplitInputSection::getRangeAndSize.
> >
> > This patch adds Size member to SectionPiece so that getRangeAndSize
> > can just return a SectionPiece instead of a std::pair<SectionPiece *,
> uint_t>.
> > Also renamed the function.
>
> [...]
>
> > --- lld/trunk/ELF/OutputSections.cpp (original)
> > +++ lld/trunk/ELF/OutputSections.cpp Sat May 21 19:41:38 2016
> > @@ -1142,9 +1142,6 @@ void EHOutputSection<ELFT>::addSectionAu
> >
> >    DenseMap<uintX_t, uintX_t> OffsetToIndex;
> >    while (!D.empty()) {
> > -    unsigned Index = Sec->Pieces.size();
> > -    Sec->Pieces.emplace_back(Offset);
> > -
> >      uintX_t Length = readEntryLength<ELFT>(D);
> >      // If CIE/FDE data length is zero then Length is 4, this
> >      // shall be considered a terminator and processing shall end.
> > @@ -1152,6 +1149,9 @@ void EHOutputSection<ELFT>::addSectionAu
> >        break;
> >      StringRef Entry((const char *)D.data(), Length);
> >
> > +    unsigned Index = Sec->Pieces.size();
> > +    Sec->Pieces.emplace_back(Offset, Length);
> > +
> >      uint32_t ID = read32<E>(D.data() + 4);
> >      if (ID == 0) {
> >        // CIE
>
> Before this commit if .eh_frame section contains only 4-byte
> terminator, we added single entry into the Pieces. Now in that case
> the Pieces is empty. But it is possible to have a symbol points to
> this .eh_frame section. In that case Section->getOffset(Body) call for
> such symbol is crashed in the EhInputSection<ELFT>::getOffset()
> because SplitInputSection<ELFT>::getSectionPiece() returns trash.
>
> On my machine it prevents to link "Hello World":
> [[
> % ld.lld --hash-style=both --build-id --eh-frame-hdr -m elf_x86_64
> -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o a.out
> /usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crt1.o
> /usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crti.o
> /usr/lib/gcc/x86_64-linux-gnu/4.7/crtbegin.o
> -L/usr/lib/gcc/x86_64-linux-gnu/4.7
> -L/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu
> -L/lib/x86_64-linux-gnu -L/lib/../lib64 -L/usr/lib/x86_64-linux-gnu
> -L/usr/lib/gcc/x86_64-linux-gnu/4.7/../../..
> -L/home/simon/work/llvm/bld/bin/../lib -L/lib -L/usr/lib main.o -lgcc
> --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s
> --no-as-needed /usr/lib/gcc/x86_64-linux-gnu/4.7/crtend.o
> /usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crtn.o
>
> % objdump -st /usr/lib/gcc/x86_64-linux-gnu/4.7/crtend.o
> ...
>
> 0000000000000000 l    d  .eh_frame      0000000000000000 .eh_frame
> 0000000000000000 l     O .eh_frame      0000000000000000 __FRAME_END__
>
> ...
>
> Contents of section .eh_frame:
>  0000 00000000                             ....
> ]]
>
> --
> Simon Atanasyan
>
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