Re: [patch+7.9] compile: Filter out -fpreprocessed

[Doug Evans <dje at google dot com>]

On Tue, Feb 3, 2015 at 11:10 AM, Mark Wielaard <mjw@redhat.com> wrote:
> On Tue, 2015-02-03 at 19:59 +0100, Jan Kratochvil wrote:
>> On Tue, 03 Feb 2015 19:50:40 +0100, Doug Evans wrote:
>> > On Fri, Jan 16, 2015 at 2:42 PM, Jan Kratochvil
>> > <jan.kratochvil@redhat.com> wrote:
>> > > [...]
>> > > It is wrong that gcc puts -fpreprocessed into DW_AT_producer - I may post a gcc
>> > > patch for it.
>> >
>> > I wasn't aware there are now rules for what can and cannot go in DW_AT_producer.
>> > DW_AT_producer has gone from being informational to having a formal
>> > spec (in the sense that something will break if, for example, a
>> > particular option is mentioned).
>> > Is this spec written down somewhere? [At least guidelines for what
>> > things may lead to breakage?]
>>
>> No. Do you have a suggestion where to put it? Should it be only a GNU
>> extension or should it be even DWARF-standardized?
>
> The gcc documentation describes it:
> https://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html
>
> -grecord-gcc-switches
>         This switch causes the command-line options used to invoke the
>         compiler that may affect code generation to be appended to the
>         DW_AT_producer attribute in DWARF debugging information. The
>         options are concatenated with spaces separating them from each
>         other and from the compiler version. See also
>         -frecord-gcc-switches for another way of storing compiler
>         options into the object file. This is the default.
>
> -gno-record-gcc-switches
>         Disallow appending command-line options to the DW_AT_producer
>         attribute in DWARF debugging information.
>
> So Jan is right that gcc adding -fpreprocessed, which doesn't affect
> code generation, but is a preprocessor option, shouldn't be there.

Thanks.

Still, there's no hint to the reader that things may break if certain rules
are not followed. It still seems like it's for informational purposes for
human readers, with no suggestion that programs use this information too.

[For completeness sake, I'm setting aside the compiler and version string.
That seemed common enough knowledge to not need documentation
as much as this does.  I realize we're now talking about -grecord-gcc-switches,
but this thread was originally about DW_AT_producer in general.]