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SubjectRe: [PATCH v2 4/6] compiler-gcc.h: add asm_inline definition
On Thu, Sep 5, 2019 at 3:45 PM Segher Boessenkool
<segher@kernel.crashing.org> wrote:
>
> [ That's not what a feature test macro is; a feature test macro allows the
> user to select some optional behaviour. Things like _GNU_SOURCE. ]

Yes and no. GNU libc defines feature test macros like you say, but
C++'s feature macros are like Rasmus/Nick are saying. I think libc's
definition is weird, I would call those "feature selection macros"
instead, because the user is selecting between some features (whether
to enable or not, for instance), rather than testing for the features.

> Why would GCC want to have macros for all features it has? That would be
> quite a few new ones every release.

Maybe GCC wouldn't, but its users, they surely would. For anything
that 1) is a new language feature, 2) breaks backwards-compatibility
with previous (or other compilers) and 3) is expected to be used by
end users, yes, it would be very useful to have.

For the same reasons C++ is adding feature test macros all over the
place nowadays and it is considered good practice (see SD-6: SG10
Feature Test Recommendations).

Cheers,
Miguel

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