[PATCH] D71509: [ELF][PowerPC] Set PltSection alignment to 4 and fix IPLT index

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

  #include <stdio.h>
  static void impl(void) { puts("meow"); }
  void thefunc(void) __attribute__((ifunc("resolver")));
  void *resolver(void) { return &impl; }
  int main(void) {
    thefunc();
    void (*theptr)(void) = &thefunc;
    theptr();
  }

GNU ld powerpc tries very hard to keep the type of `thefunc` as `STT_IFUNC` and uses `R_PPC64_IRELATIVE`

  % ~/llvm/Release/bin/clang -fPIC -fuse-ld=bfd -g b.c -o b.bfd
  % readelf -r b.bfd
  Relocation section '.rela.dyn' at offset 0x380 contains 3 entries:
      Offset             Info             Type               Symbol's Value  Symbol's Name + Addend
  000000001001ff08  0000000200000026 R_PPC64_ADDR64         0000000000000000 __gmon_start__ + 0
  000000001001ff28  00000000000000f8 R_PPC64_IRELATIVE                         10000660
  0000000010020028  00000000000000f8 R_PPC64_IRELATIVE                         10000660
  ...
  % readelf -Ws b | grep thefunc
      50: 0000000010000480     0 NOTYPE  LOCAL  DEFAULT   12 00000019.plt_call.thefunc
      66: 0000000010000660    32 IFUNC   GLOBAL DEFAULT [<localentry>: 8]    12 thefunc
  % ./b.bfd
  meow
  meow



  % ~/llvm/Release/bin/clang -fPIC -fuse-ld=lld -g b.c -o b.lld
  % readelf -r b.lld
  Relocation section '.rela.dyn' at offset 0x468 contains 1 entry:
      Offset             Info             Type               Symbol's Value  Symbol's Name + Addend
  0000000010030be0  00000000000000f8 R_PPC64_IRELATIVE                         10010700
  ...
  % readelf -Ws b.lld | grep thefunc                                          
      22: 00000000100108e8    20 FUNC    LOCAL  DEFAULT   14 __plt_thefunc
      39: 00000000100109b8     0 FUNC    GLOBAL DEFAULT [<localentry>: 8]    17 thefunc
  % ./b
  meow
  Inconsistency detected by ld.so: dl-runtime.c: 80: _dl_fixup: Assertion `ELFW(R_TYPE)(reloc->r_info) == ELF_MACHINE_JMP_SLOT' failed!


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D71509/new/

https://reviews.llvm.org/D71509