[Diffusion] rL309526: DebugInfo: Use base address selection entries in debug_ranges to reduce…

[Tamas Berghammer via Phabricator via llvm-commits]

tberghammer added subscribers: llvm-commits, tberghammer.
tberghammer raised a concern with this commit.
tberghammer added a comment.

Hi David,

This CL caused a regression in LLDB by generating some incorrect relocations for the debug info. To reproduce:

Compile the following source code using ToT clang (trunk 309523) for x86_64-unknown-linux-gnu with "clang -g -c -o ns2.cpp ns2.o"

  inline int a() { return 1; }
  void b() { a(); }
  void c() {}

Running "objdump -W -r ns2.o" will show the following data:

  Contents of the .debug_ranges section:
  
      Offset   Begin    End
      00000000 ffffffffffffffff 0000000000000000 (base address)
      00000000 0000000000000000 0000000000000016 
      00000000 0000000000000020 0000000000000026 
      00000000 0000000000000000 000000000000000b 
      00000000 <End of list>
  
  ....
  
  RELOCATION RECORDS FOR [.debug_ranges]:
  OFFSET           TYPE              VALUE 
  0000000000000008 R_X86_64_64       .text
  0000000000000030 R_X86_64_64       .text._Z1av
  0000000000000038 R_X86_64_64       .text._Z1av

Looking at the data it will apply both the base address entry and the relocation entry for the 4th row in the debug_ranges section what will mean they will end up with invalid values.

Note: As far as I can tell LLDB doesn't support these base address entries but that should be an easy fix on the LLDB side what I can take care of once clang emits the correct data.


Users:
  dblaikie (Author)
  tberghammer (Auditor)

https://reviews.llvm.org/rL309526