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

[David Blaikie via cfe-dev]

On Wed, Feb 21, 2018 at 9:07 AM Adrian Prantl <aprantl at apple.com> wrote:

>
> On Feb 21, 2018, at 9:04 AM, David Blaikie <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).

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


>
> -- adrian
>
>
> On Wed, Feb 21, 2018 at 8:18 AM Adrian Prantl <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> 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> 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.
>>>
>>> _______________________________________________
>>> cfe-dev mailing list
>>> cfe-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>
>>
>>
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