Re: Mismatch between newlib and glibc regarding fileno

On Fri, Feb 9, 2024 at 8:30 AM Torbjorn SVENSSON
<[email protected]> wrote:
>
> Hi all,
>
> I've been trying to run tests for arm-none-eabi on GCC14 tree.
> What I've seen is that fileno() is not available. If you look though the
> header files, I see that this is guarded by __POSIX_VISIBLE and due to a
> recent change in the GCC testsuite (part of PR96395), they moved the
> test case to gcc/testsuite/c-c++-common/analyzer/fileno-1.c and then
> invoke it with g++ and -std=c++98. With this change, strict ANSI is
> defined, but not __POSIX_VISIBLE.

Note the testcase failure is recorded as https://gcc.gnu.org/PR113278 .

>
> If I run the same test on the native g++ tool in Ubuntu, I instead get
> that __USE_POSIX is set (the guard for fileno() in glibc), so this
> differs from the behavior noticed with newlib.

That is also due to _GNU_SOURCE being defined for C++ for Linux/g++. I
think this is just a GCC testcase issue rather than something needing
to be fixed in newlib even.

Thanks,
Andrew

>
>
> Is it correct that newlib does not define __POSIX_VISIBLE when g++ is
> invoked with -std=c++98 (or any other standard that does not use the GNU
> extensions)?
> It can also be seen using gcc with -std=c11 for example, so it's not
> strictly a C vs C++ issue.
>
>
> The expression used in glibc:
> https://github.com/bminor/glibc/blob/master/include/features.h#L335
>
> The expression used in newlib:
> https://sourceware.org/git/?p=newlib-cygwin.git;a=blob;f=newlib/libc/include/sys/features.h;h=6a925c87e9ec333fc51538201aa7b52d24b3ca5b;hb=refs/heads/main#l148
>
>
> Kind regards,
> Torbjörn