[PATCH] D95518: [Debug-Info][XCOFF] support dwarf for XCOFF for assembly output

[ChenZheng via Phabricator via llvm-commits]

shchenz added inline comments.


================
Comment at: llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp:1804-1807
+  // When -function-sections is enabled, generating function section end symbol
+  // to tell debug line section where is the end of current function section.
+  if (TM.getFunctionSections() && !MAI->usesDwarfFileAndLocDirectives() &&
+      MMI->hasDebugInfo())
----------------
jasonliu wrote:
> shchenz wrote:
> > hubert.reinterpretcast wrote:
> > > @jasonliu, I'd like your analysis of how this interacts with explicit sections.
> > `explicit sections` are generated when `-fdata-sections` is enabled? If so, I think debugging functionality should not be impacted. We only need to worry about the "text" section for debug line. For `explicit sections` functionality, I guess it should not be impacted too as we only add new labels, not data, like `vbyte`, `byte`
> > 
> > Anyway, your input is appreciated @jasonliu 
> It seems that we want to generate a section end label on every text csect here.
> If that's the case, then it doesn't seem like we are generating them correctly when explicit section for text section is enabled. An example would be:
> ```
> int bar() {return 1;}
> int __attribute__((section ("explicit_main_sec"))) main() {
>   return bar();
> }
> ```
> I don't see a `L..sec_end` for `.text[PR]`.
> 
> A side note when I was trying things: it seems we have a subtle bug when we enables -function-sections and specify an explicit section for a function. We don't generate a label for the function entry point in this case, and we don't have the correct function entry point stored in the function descriptor section. 
> The bug is not related to this patch, and we need to fix it in another patch. But it affects how we want to construct a test case in this patch.
Good catch. We need to generate section end symbol for the explicit section too. Fixed in the new patch.

I found one issue, not sure if it is the same one as you found:
for the case you given, if we compile it with `-ffunction-sections`, we will get some linking error:
```
> clang 4.c -ffunction-sections          
ld: 0711-317 ERROR: Undefined symbol: .main
ld: 0711-345 Use the -bloadmap or -bnoquiet option to obtain more information.
clang-13: error: linker command failed with exit code 8 (use -v to see invocation)
```


================
Comment at: llvm/test/DebugInfo/XCOFF/empty.ll:51
+; ASM32-NEXT:   li 4, 0
+; ASM32-NEXT:  L..tmp1:
+; ASM32-NEXT:  L..tmp2:
----------------
jasonliu wrote:
> It might not be big deal, but it seems we are generating an extra label for no reason?
Not sure, this should be also exist without -g.


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  https://reviews.llvm.org/D95518/new/

https://reviews.llvm.org/D95518