[PATCH] LLVMSymbolizer: Use alternative method if no inlining frames found.

[Alexey Samsonov]

Hi Will,

On Thu, Oct 17, 2013 at 12:51 AM, Will Dietz <w at wdtz.org> wrote:

> Fixes bug exposed by tsan lit tests where addresses fail to be
> symbolized on my system (x86_64 linux).
>
> An example of this failure can be seen with this binary[1]:
>
> $ unxz ./thread_leak.3.c.tmp.xz
>
> Using llvm-symbolizer from ToT:
>
> $ echo ./thread_leak3.c.tmp 0x020560 | ~/llvm/build/bin/llvm-symbolizer
> __interceptor_pthread_create
> ??:0:0
>
> And after:
>
> $ echo ./thread_leak3.c.tmp 0x020560|~/llvm/build/bin/llvm-symbolizer
> __interceptor_pthread_create
>
> /home/will/llvm/latest/projects/compiler-rt/lib/tsan/rtl/tsan_interceptors.cc:876:0
>
> Proposed patch attached.


Interesting. I agree that llvm-symbolizer should perform at least as good
with --inlining=true
than without it, but the fix should probably go the DWARF parser in
DebugInfo library.

Here's the DWARF entry for __interceptor_pthread_create in your binary:

0x0002c37a:   DW_TAG_subprogram [182] *
                DW_AT_external [DW_FORM_flag_present]   (true)
                DW_AT_name [DW_FORM_strp]       ( .debug_str[0x00012957] =
"__interceptor_pthread_create")
                DW_AT_decl_file [DW_FORM_data1] (0x01)
                DW_AT_decl_line [DW_FORM_data2] (0x036b)
                DW_AT_type [DW_FORM_ref4]       (cu + 0x49a0 =>
{0x00014e6e})
                DW_AT_low_pc [DW_FORM_addr]     (0x0000000000020560)
                DW_AT_high_pc [DW_FORM_data8]   (0x000000000000015f)
<-------------------- [1]
                DW_AT_frame_base [DW_FORM_exprloc]      (<0x1> 9c )
                DW_AT_Unknown_2117 [DW_FORM_flag_present]       (true)
                DW_AT_sibling [DW_FORM_ref4]    (cu + 0x1c267 =>
{0x0002c735})

[1] DW_AT_high_pc has different DW_FORM here and actually means the size of
the functions, not its largest address.
My guess is DWARF parser doesn't know about this and fails to build a
correct address range for the function. I'm going
to investigate this soon.

Thanks for the reproducer!


> ~Will
>
> [1] http://wdtz.org/files/thread_leak3.c.tmp.xz
>
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>
>


-- 
Alexey Samsonov, MSK
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