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

[David Blaikie via cfe-dev]

On Wed, Feb 21, 2018 at 9:13 AM Adrian Prantl <aprantl at apple.com> wrote:

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

Ah, right you are!

> (& certainly if you've got column info on, it'll change quite a lot)
>
>
> That's might be the case, though.
>

*nod*


>
> -- adrian
>
>
>
>>
>> -- 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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