[PATCH] D38721: [ELF] - Teach LLD to report line numbers for data symbols.

[George Rimar via Phabricator via llvm-commits]

grimar added inline comments.


================
Comment at: ELF/InputSection.cpp:292
+  // which describes variables and their locations.
+  if (Sym.Type == STT_OBJECT) {
+    if (Optional<std::pair<std::string, unsigned>> FileLine =
----------------
ruiu wrote:
> grimar wrote:
> > ruiu wrote:
> > > Are you sure that functions would never have type STT_OBJECT?
> > It's interesting. Specification says functions and other executable code should be of type STT_FUNC:
> > http://www.sco.com/developers/gabi/2000-07-17/ch4.symtab.html
> > So at least it does not seem correct.
> > 
> > At the same time it looks possible to do that:
> > ```
> > .section .text.fn,"ax", at progbits,unique,0
> > .globl fn
> > .type fn, at object
> > fn:
> >  nop
> > 
> > .section .text.fn2,"ax", at progbits,unique,0
> > .globl fn2
> > .type fn2, at function
> > fn2:
> >  callq fn at PLT
> > ```
> > 
> > And you'll get
> > ```
> >      4: 0000000000400079     0 FUNC    GLOBAL DEFAULT    1 fn2
> >      7: 0000000000400078     0 OBJECT  GLOBAL DEFAULT    1 fn
> > ```
> > 
> > We probably can fallback to always use .debug_line:
> > ```
> >   if (Sym.Type == STT_OBJECT)
> >     if (Optional<std::pair<std::string, unsigned>> FileLine =
> >             File->getVariableLoc(Sym.getName()))
> >       return createFileLineMsg(FileLine->first, FileLine->second);
> > 
> >   if (Optional<DILineInfo> Info = File->getDILineInfo(this, Offset))
> >     return createFileLineMsg(Info->FileName, Info->Line);
> > ```
> > 
> > At least such behavior does not seem harmful for me. 
> > Do you think we should ? (I am not sure because with assembly it is possible
> > to do many things, and particulary this one seems violates ELF spec, not sure we
> > should even think about supporting that until it is reported useful).
> > 
> > 
> Well, I think what I was trying to say is that we don't need to think about it too deeply. Why don't you just attempt both? First, try to get line info as a function, and if it fails, try as a variable.
Done.


https://reviews.llvm.org/D38721