Re: ac_sys_largefile / fseeko problem

[Guido Draheim]

Guido Draheim schrieb:
> Paul Eggert schrieb:
>
> > Guido Draheim <address@hidden> writes:
> >
> >
> > > I am using
> > > AC_SYS_LARGEFILE
> > > AC_CHECK_FUNCS(ftello fseeko)
> >
> >
> >
> > Use AC_FUNC_FSEEKO rather than AC_CHECK_FUNCS(fseeko).
> > That should work around your problems.
>
> Thanks. However, that macro still calls the glibc
> behavior a bug, which I think is simply true. The
> glibc cvs stdio.h should be fixed, - atleast do export
> fseeko when #def __USE_FILE_OFFSET64 is set!! - just in
> order to avoid that silent callframe-mismatch. In other
> words, export the REDIRECT atleast when a redirect-call
> is required to make things to function properly.
>
> This mode is easily achieved, in the glibc stdio.h part
> on fseeko: delete the __USE_LARGEFILE ifdefs within the
> #else-part opened by that #ifndef __USE_FILE_OFFSET64.
>
> This minimal change is strictly required unless glibc
> maintainers like to see the next program to delete some
> large database with an innocent fseeko call of a
> software ported to lfs mode running on a glibc system.
> Note that C compilers wouldn't even warn about the
> missing fseeko declaration unless -Wall or similar was
> given.

I had a second look at current glibc cvs - the
libio/stdio.h does have a different order for the
two ifdefs but still has the problematic behavior
of ommitting fseeko when strictly required through
the existance of __USE_FILE_OFFSET64


#ifdef __USE_LARGEFILE
# ifndef __USE_FILE_OFFSET64
/* Seek to a certain position on STREAM.  */
extern int fseeko (FILE *__stream, __off_t __off, int __whence) __THROW;
/* Return the current position of STREAM.  */
extern __off_t ftello (FILE *__stream) __THROW;
# else
#  ifdef __REDIRECT
extern int __REDIRECT (fseeko,
                       (FILE *__stream, __off64_t __off, int __whence) __THROW,
                       fseeko64);
extern __off64_t __REDIRECT (ftello, (FILE *__stream) __THROW, ftello64);
#  else
#   define fseeko fseeko64
#   define ftello ftello64
#  endif
# endif
#endif

and it should be patched atleast to be:

#ifndef __USE_FILE_OFFSET64
# ifdef __USE_LARGEFILE
/* Seek to a certain position on STREAM.  */
extern int fseeko (FILE *__stream, __off_t __off, int __whence) __THROW;
/* Return the current position of STREAM.  */
extern __off_t ftello (FILE *__stream) __THROW;
# endif
#else
# ifdef __REDIRECT
extern int __REDIRECT (fseeko,
                       (FILE *__stream, __off64_t __off, int __whence) __THROW,
                       fseeko64);
extern __off64_t __REDIRECT (ftello, (FILE *__stream) __THROW, ftello64);
# else
#   define fseeko fseeko64
#   define ftello ftello64
# endif
#endif

Personally, I think it would be the best to simply
add a global change in features.h

 #if defined _FILE_OFFSET_BITS && _FILE_OFFSET_BITS == 64
 # define __USE_FILE_OFFSET64    1
+# ifndef __USE_LARGEFILE
+# define __USE_LARGEFILE 1
+# endif
 #endif

This should avoid callframe-mismatches in all futures cases
where glibc developers decide to do things differently
without a need and differently than all other systems.

The missing fseeko-export might be called a feature-flaw
by glibc maintainers, the callframe mismatch is a plain
bug, IMHO a severe bug as all silent errors should be
called that can trash your database files.

-- cheers, guido            http://ac-archive.sf.net/largefile