llvm dev - Aug 2016 - CodeView and "line 0" ?

I've been playing with Fred Riss's "line 0" patch for DWARF
(https://reviews.llvm.org/D16569) but in adapting it for current trunk,
I find the DwarfDebug stuff has been refactored to allow either DWARF
or CodeView.  That's all good, but the question is whether the "line
0"
patch should be DWARF-specific or common.  The DWARF spec explicitly
states that code not associated with any particular source location 
should be associated with line number 0.  I don't know what CodeView
(or debuggers that consume CodeView) would think of seeing "line 0"
show
up in the debug info.

Does anybody know?
Thanks,
--paulr

Note that clang is also assigning line 0 to code that doesn't have a
corresponding source location. So CodeView needs to deal with this already,
though I don't know how it currently handles this.

-- adrian
> On Aug 17, 2016, at 11:43 AM, Robinson, Paul via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> I've been playing with Fred Riss's "line 0" patch for
DWARF
> (https://reviews.llvm.org/D16569) but in adapting it for current trunk,
> I find the DwarfDebug stuff has been refactored to allow either DWARF
> or CodeView.  That's all good, but the question is whether the
"line 0"
> patch should be DWARF-specific or common.  The DWARF spec explicitly
> states that code not associated with any particular source location 
> should be associated with line number 0.  I don't know what CodeView
> (or debuggers that consume CodeView) would think of seeing "line
0" show
> up in the debug info.
> 
> Does anybody know?
> Thanks,
> --paulr
> 
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev

I mean, we just skip over instructions without a DebugLoc:

void CodeViewDebug::beginInstruction(const MachineInstr *MI) {
  DebugHandlerBase::beginInstruction(MI);

  // Ignore DBG_VALUE locations and function prologue.
  if (!Asm || !CurFn || MI->isDebugValue() ||
      MI->getFlag(MachineInstr::FrameSetup))
    return;
  DebugLoc DL = MI->getDebugLoc();
  if (DL == PrevInstLoc || !DL)
    return;
  maybeRecordLocation(DL, Asm->MF);
}

Seems reasonable to extend the condition with ' || DL->getLine() ==
0'. I'm
not aware of a good way to say "this instruction is not associated with any
line" in CodeView.

On Wed, Aug 17, 2016 at 12:51 PM, Adrian Prantl via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Note that clang is also assigning line 0 to code that doesn't have a
> corresponding source location. So CodeView needs to deal with this already,
> though I don't know how it currently handles this.
>
> -- adrian
>
> > On Aug 17, 2016, at 11:43 AM, Robinson, Paul via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > I've been playing with Fred Riss's "line 0" patch
for DWARF
> > (https://reviews.llvm.org/D16569) but in adapting it for current
trunk,
> > I find the DwarfDebug stuff has been refactored to allow either DWARF
> > or CodeView.  That's all good, but the question is whether the
"line 0"
> > patch should be DWARF-specific or common.  The DWARF spec explicitly
> > states that code not associated with any particular source location
> > should be associated with line number 0.  I don't know what
CodeView
> > (or debuggers that consume CodeView) would think of seeing "line
0" show
> > up in the debug info.
> >
> > Does anybody know?
> > Thanks,
> > --paulr
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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