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Re: Problem caused by removed function and its remaining dwarf entry


On Fri, Feb 13, 2015 at 5:36 PM, Senthil Kumar Selvaraj
<senthil_kumar.selvaraj@atmel.com> wrote:
> On Fri, Feb 13, 2015 at 05:07:08PM +0800, Terry Guo wrote:
>> Hi there,
>>
>> I have an unused function foo in file foo.c which is then compiled with -O0
>> and -ffunction-sections. The foo function will be kept in foo.o and will get
>> a dwarf entry in dwarf section. Lately the --gc-section will discard this
>> unused function and its section, but won't clean its dwarf entry. Then when
>> set breakpoint for function foo under gdb, gdb will use such remaining and
>> incorrect dwarf entry to set breakpoint for no-longer-existing function foo.
>> For embedded target, such incorrect information like PC value will be passed
>> to hardware debug unit to set breakpoint, this will cause trouble.
>>
>> Is it possible to remove corresponding dwarf entry after --gc-section
>> discarded sections? Please help. Thanks in advance.
>
> I encountered this a while back (see
> https://gcc.gnu.org/ml/gcc/2014-01/msg00116.html).
>
> AFAIK, this requires changes in the way the compiler emits DWARF. Right
> now, all debug info for a compilation unit are grouped together, and
> unless the linker understands DWARF binary format, it can't removing the
> entries.
>
> So, we'd need to make the compiler emit the appropriate DW_TAGs, and
> make gdb understand them.
>
> Regards
> Senthil

Totally agree with your idea and patch. Do you have any plan to
continue your work to get gcc accept your patch? I think it will be a
very helpful feature.

BR,
Terry


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