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

Wed Dec 23 09:45:39 PST 2020

tmsriram added a comment.

In D93747#2470189 <https://reviews.llvm.org/D93747#2470189>, @hoy wrote:

> In D93747#2470178 <https://reviews.llvm.org/D93747#2470178>, @tmsriram wrote:
>
>> In D93747#2469556 <https://reviews.llvm.org/D93747#2469556>, @hoy wrote:
>>
>>>> In D93656 <https://reviews.llvm.org/D93656>, @dblaikie wrote:
>>>> Though the C case is interesting - it means you'll end up with C functions with the same DWARF 'name' but different linkage name. I don't know what that'll do to DWARF consumers - I guess they'll probably be OK-ish with it, as much as they are with C++ overloading. I think there are some cases of C name mangling so it's probably supported/OK-ish with DWARF Consumers. Wouldn't hurt for you to take a look/see what happens in that case with a debugger like gdb/check other cases of C name mangling to see what DWARF they end up creating (with both GCC and Clang).
>>>
>>> I did a quick experiment with C name managing with GCC and -flto. It turns out the `DW_AT_linkage_name` field of `DW_TAG_subprogram` is never set for C programs. 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. I'm inclined to have it under a switch. What do you think?
>>
>> Just a thought, we could always check if rawLinkageName is set and only set it when it is not null.  That seems safe without needing the option. Not a strong opinion.
>
> It seems that the demangler of the debugger is not able to handle an uniquefied name, even if the debug record originally comes with a linkage name.

Yep, the demangler (which can be checked with c++filt) is very restricted on what comes after the "."  It can be either numbers or characters but not a mix of the two.  I guess we can enhance it.

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https://reviews.llvm.org/D93747