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

[David Blaikie via llvm-commits]

On Sun, Jul 30, 2017 at 4:49 PM Tamas Berghammer via Phabricator <
reviews at reviews.llvm.org> wrote:

> 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.
>

Ah, I see what you mean - the base address selection entry has to be reset.
Makes sense. Thanks! Will get that fixed ASAP.


>
> 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
>
>
>
>
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