[PATCH] D62106: [X86] Support -fno-plt __tls_get_addr calls

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

In D62106#1572575 <https://reviews.llvm.org/D62106#1572575>, @nikic wrote:

> I'm seeing linker failures that I suspect are related to this change:
>
>   /usr/bin/ld: /home/nikic/rust/foo/libtest2.rlib(test2.test2.3a1fbbbh-cgu.0.rcgu.o): TLS transition from R_X86_64_TLSLD to R_X86_64_TPOFF32 against `_ZN5test24TEST17h9cebda1c5e0bffdeE' at 0x4 in section `.text._ZN5test28get_test17h7831513ccc936b83E' failed
>
>
> Old:
>
>   0000000000000000 <_ZN5test28get_test17h7831513ccc936b83E>:
>      0:   50                      push   %rax
>      1:   48 8d 3d 00 00 00 00    lea    0x0(%rip),%rdi        # 8 <_ZN5test28get_test17h7831513ccc936b83E+0x8>
>               4: R_X86_64_TLSLD   _ZN5test24TEST17h9cebda1c5e0bffdeE-0x4
>      8:   e8 00 00 00 00          callq  d <_ZN5test28get_test17h7831513ccc936b83E+0xd>
>               9: R_X86_64_PLT32   __tls_get_addr-0x4
>      d:   48 8b 80 00 00 00 00    mov    0x0(%rax),%rax
>               10: R_X86_64_DTPOFF32   _ZN5test24TEST17h9cebda1c5e0bffdeE
>     14:   59                      pop    %rcx
>     15:   c3                      retq
>
>
> New:
>
>   0000000000000000 <_ZN5test28get_test17h7831513ccc936b83E>:
>      0:   50                      push   %rax
>      1:   48 8d 3d 00 00 00 00    lea    0x0(%rip),%rdi        # 8 <_ZN5test28get_test17h7831513ccc936b83E+0x8>
>               4: R_X86_64_TLSLD   _ZN5test24TEST17h9cebda1c5e0bffdeE-0x4
>      8:   ff 15 00 00 00 00       callq  *0x0(%rip)        # e <_ZN5test28get_test17h7831513ccc936b83E+0xe>
>               a: R_X86_64_GOTPCREL    __tls_get_addr-0x4
>      e:   48 8b 80 00 00 00 00    mov    0x0(%rax),%rax
>               11: R_X86_64_DTPOFF32   _ZN5test24TEST17h9cebda1c5e0bffdeE
>     15:   59                      pop    %rcx
>     16:   c3                      retq
>
>
> I'm not really familiar with TLS relocations -- do you have any pointers on what could be going wrong here?




  % clang -fno-plt -fpic a.cc -Wa,-mrelax-relocations=no -fuse-ld=gold
  % clang -fno-plt -fpic a.cc -Wa,-mrelax-relocations=no -fuse-ld=lld
  % clang -fno-plt -fpic a.cc -Wa,-mrelax-relocations=no -fuse-ld=bfd
  /usr/bin/ld.bfd: /tmp/a-9fd9f7.o: TLS transition from R_X86_64_TLSLD to R_X86_64_TPOFF32 against `_ZL1a' at 0x17 in section `.text' failed



  # bfd/elf-x86-64.c:elf_x86_64_check_tls_transition
  ...
      if (largepic)
        return r_type == R_X86_64_PLTOFF64;
      else if (indirect_call)
        return r_type == R_X86_64_GOTPCRELX; // it doesn't allow R_X86_64_GOTPCREL
      else
        return (r_type == R_X86_64_PC32 || r_type == R_X86_64_PLT32);

ld.bfd doesn't allow R_X86_64_GOTPCREL. You can work around the issue with:

  % clang -fno-plt -fpic a.cc -Wa,-mrelax-relocations=yes -fuse-ld=bfd

I'll file a bug against binutils-gdb.


Repository:
  rL LLVM

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  https://reviews.llvm.org/D62106/new/

https://reviews.llvm.org/D62106