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

[Jason Liu via Phabricator via llvm-commits]

jasonliu 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())
----------------
shchenz wrote:
> 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)
> ```
Yes, it's the same bug.
I feel the current way of handling end of text csect is not very robust.
A few more ways to break it:
1.
```
int __attribute__((section ("explict_text_sec"))) foo() {
  return 1;
}
int bar2() {return 1;}
int __attribute__((section ("explict_text_sec"))) bar() {
  return bar2();
}

```
2. 
It seems when C++ exception handling is enabled, and eh instruments are generated, then we will not have the label `L..sec_end` on the correct location. 
A sample program would be:
```
int foo(){
  try { throw 1;}
  catch(...) { return 1;}
  return 0;
}
```


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

https://reviews.llvm.org/D95518