Problem caused by removed function and its remaining dwarf entry

[Senthil Kumar Selvaraj]

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