[PATCH] D67053: [LLD] [COFF] Resolve source locations for undefined references using dwarf

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added inline comments.


================
Comment at: test/COFF/undefined-symbol-dwarf.s:15
+# CHECK-NEXT: >>> referenced by {{.*}}.o:(myptr)
+
+	.text
----------------
mstorsjo wrote:
> MaskRay wrote:
> > clang -S output is verbose. Many directives in this file are not significant and they should be deleted to improve readability. The relocations are not resolved. Does that cause any problem?
> > clang -S output is verbose. Many directives in this file are not significant and they should be deleted to improve readability.
> 
> Yes, I guess I could trim out some. This is also built with -O0 to make sure the inline function ends up in a separate comdat (`.section .text$_ZN1A5afuncEv` below) to test that resolving references in different sections work, but I guess I could use some optimization with `-fno-inline` or something similar to keep them separate.
> 
> However, I'm a little weary of doing too much manual cleanups of it, if it would make the debug info mismatch the actual code. I'm not very proficient in DWARF so I don't know for sure exactly what needs to match what here, and which of the debug sections could be removed without breaking it.
> 
> > The relocations are not resolved. Does that cause any problem?
> 
> Um, what do you mean? The errors about undefined symbols? That's the whole point of the test; to have undefined references, that we try to resolve back to source line numbers using the debug info.
Can you take a look at test/ELF/debug-line-str.s and test/ELF/debug-line-obj.s? They are still a bit verbose in my opinion but is much conciser than this file..

.debug* sections (DWARF) in object files contains relocations (e.g. `.secrel32  .Linfo_string1`). They have to be resolved so that they can be symbolized by lib/DebugInfo/Symbolize. In the ELF port of lld, ELF/DWARF.cpp provides the relocation resolver functionality.

Does COFF need a counterpart? To be honest I know very little about COFF. I'll make some investigation into this. Meanwhile, can you test this patch on some larger programs, DLLs with multiple object files, etc?


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https://reviews.llvm.org/D67053