Re: Mismatch between newlib and glibc regarding fileno

[Corinna Vinschen <vinschen@redhat.com>]

On Feb 12 16:36, Torbjorn SVENSSON wrote:
> On 2024-02-09 17:54, Corinna Vinschen wrote:
> > On Feb  9 08:40, Andrew Pinski wrote:
> > > On Fri, Feb 9, 2024 at 8:30 AM Torbjorn SVENSSON
> > > <torbjorn.svensson@foss.st.com> 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.
> > 
> > Along these lines, note the Linux man page for fileno:
> > 
> >      STANDARDS
> >         POSIX.1-2008.
> > 
> >      HISTORY
> >        POSIX.1-2001.
> > 
> > and the feature test in GLibc's stdio.h:
> > 
> >      #ifdef  __USE_POSIX
> >      /* Return the system file descriptor for STREAM.  */
> >      extern int fileno (FILE *__stream) __THROW __wur;
> >      #endif /* Use POSIX.  */
> > 
> > 
> > Corinna
> > 
> Okay, so newlib is more restrictive than glibc on this topic.
> I will prepare a patch for test cases in GCC with defining _POSIX_SOURCE  so
> that the test cases succeed for newlib.

It looks like it.  But I do wonder if that's really intended by glibc.
I ran a quick test, first under newlibL

  $ g++ -std=c++98 -E -dM /usr/include/features.h | grep VISIBLE
  #define __LARGEFILE_VISIBLE 0
  #define __ISO_C_VISIBLE 1999
  #define __XSI_VISIBLE 0
  #define __GNU_VISIBLE 0
  #define __BSD_VISIBLE 0
  #define __POSIX_VISIBLE 0
  #define __SVID_VISIBLE 0
  #define __ATFILE_VISIBLE 0
  #define __MISC_VISIBLE 0

then under glibc:

  $ g++ -std=c++98 -E -dM x.cc | grep '#define __USE'
  #define __USE_UNIX98 1
  #define __USE_FORTIFY_LEVEL 0
  #define __USE_ISOC11 1
  #define __USE_ISOC95 1
  #define __USE_ISOC99 1
  #define __USE_XOPEN 1
  #define __USE_XOPEN2K 1
  #define __USE_POSIX199506 1
  #define __USE_GNU 1
  #define __USE_XOPEN2KXSI 1
  #define __USE_XOPEN2K8 1
  #define __USE_POSIX 1
  #define __USER_LABEL_PREFIX__ 
  #define __USE_MISC 1
  #define __USE_POSIX2 1
  #define __USE_LARGEFILE64 1
  #define __USE_POSIX199309 1
  #define __USE_XOPEN2K8XSI 1
  #define __USE_LARGEFILE 1
  #define __USE_XOPEN_EXTENDED 1
  #define __USE_DYNAMIC_STACK_SIZE 1
  #define __USE_ATFILE 1

How is it possible that with -std=c++98, everything and the kitchen sink
is enabled?  Is that really correct?!?


Corinna