[cfe-dev] [Debug Info] Wrong column numbers come from macros

[Adrian Prantl via cfe-dev]

> On Feb 21, 2018, at 9:11 AM, David Blaikie <dblaikie at gmail.com> wrote:
> 
> 
> 
> On Wed, Feb 21, 2018 at 9:07 AM Adrian Prantl <aprantl at apple.com <mailto:aprantl at apple.com>> wrote:
> 
>> On Feb 21, 2018, at 9:04 AM, David Blaikie <dblaikie at gmail.com <mailto:dblaikie at gmail.com>> wrote:
>> 
>> Not sure I follow there, though, Adrian - the semantics don't dictate just how we could model this in a debugger.. (similarly how our diagnostics can provide more detail rather than modelling a macro expansion as though it was all written at the macro invocation point)
>> 
>> I think we've talked about using something like inlining to represent macro expansions, for example - to provide help with the debugging experience.
> 
> Something like this would certainly be doable, but I'm somewhat concerned that we wouldn't be able to reproduce a compilation from preprocessed source any more. I suppose we could extend #line with inline information to reflect the macro expansion, though.
> 
> I think that might already be true - if it's a multi-line macro, for example, it'll change the line numbers of the file (& result in the multiple lines of the macro being attributed to different lines, rather than all to the same line).

As far as I rememeber, a multi-line macro gets expanded onto a single line.

> 
> (& certainly if you've got column info on, it'll change quite a lot)

That's might be the case, though.

-- adrian
>  
> 
> -- adrian
> 
>> 
>> On Wed, Feb 21, 2018 at 8:18 AM Adrian Prantl <aprantl at apple.com <mailto:aprantl at apple.com>> wrote:
>> This is not even a limitation of DWARF but rather mandated by the C specification. The C language standard explicitly specifies that all code in a (multi-line) macro expansion shall behave as if it were on the same line as the macro invocation. I understand that it technically doesn't say anything about columns and perhaps we could do something for single-line macros there, but this is basically the root of the issue.
>> 
>> 
>> -- adrian
>> 
>>> On Feb 21, 2018, at 8:00 AM, David Blaikie <dblaikie at gmail.com <mailto:dblaikie at gmail.com>> wrote:
>>> 
>>> I think it's a matter of this being the best of no great options available in DWARF, but I personally haven't given it a great deal of thought.
>>> 
>>> On Tue, Feb 20, 2018 at 10:34 PM Alex Denisov via cfe-dev <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>> wrote:
>>> Hi,
>>> 
>>> I see an issue with debug info and macro. Here is an example:
>>> 
>>> #define f(x) x
>>> ...
>>> int a = f(b + c);
>>>         ^
>>> 
>>> The debug information for each node in 'b + c' points to the 'f' (see the caret). I expect it to point to the actual source location.
>>> 
>>> I assume that is a known issue, but I could find neither explanation nor bug report.
>>> Can somebody shed some light on the issue?
>>> 
>>> Cheers,
>>> Alex.
>>> 
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>> 

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