[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:
> 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).




https://reviews.llvm.org/D38721