[PATCH] D93747: Rename debug linkage name with -funique-internal-linkage-names

Tue Jan 5 18:23:19 PST 2021

hoy added a comment.

In D93747#2481073 <https://reviews.llvm.org/D93747#2481073>, @dblaikie wrote:

> In D93747#2481053 <https://reviews.llvm.org/D93747#2481053>, @tmsriram wrote:
>
>> In D93747#2480442 <https://reviews.llvm.org/D93747#2480442>, @dblaikie wrote:
>>
>>> @tmsriram - any ideas what your case/example was like that might've caused degraded debugging experience? Would be good to understand if we're producing some bad DWARF with this patch/if there might be some way to avoid it (as it seems like gdb can handle mangled names/overloading in C in this example I've tried)
>>
>> I haven't seen anything that caused degraded debugging experience.  I am interested in this as we do look at this field for the purposes of profile attribtution for calls that are inlined.  My comment was that we don't need to create this if it didn't already exist.  I am not fully aware of what would happen if we did it all the time.
>
> Ah, sorry, I got confused as to who's comment I was reading. I see it was @hoy who said:
>
>> If set, the gdb debugger will use that field to match the user input and set breakpoints. Therefore, giving DW_AT_linkage_name a uniquefied name prevents the debugger from setting a breakpoint based on source names unless the user specifies a decorated name.
>>
>> Hence, this approach sounds like a workaround for us when the profile quality matters more than debugging experience.
>
> So I'm still a bit confused. My test doesn't seem to demonstrate the issue with setting a linkage name preventing the debugger from setting a breakpoint based on the source name?
>
> Suggesting that gdb isn't using the DW_AT_name at all for "break <function name>" but instead demangling and stripping off the extras from the linkage name, and since it can't demangle this uniquified name (unlike the mangled name used when using the overloadable attribute) that degrades the debugger user experience? I'd have to test that in more detail/with some hand-hacked DWARF.

Yes, I think in your case the linage name can be demangled by the debugger. In my previous experiment, the uniquefied names could not be demangled therefore I was not able to breakpoint.

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https://reviews.llvm.org/D93747