Re: libgcov, fork, and mingw (and other targets without the full POSIX set)

[Mark Wielaard <mark@klomp.org>]

Hi,

On Fri, 2023-12-01 at 13:09 +0100, Jakub Jelinek via Gcc wrote:
> On Fri, Dec 01, 2023 at 01:03:01PM +0100, Jan Hubicka via Gcc wrote:
> > > On Dez 01 2023, Richard Biener via Gcc wrote:
> > > 
> > > > Hmm, so why's it then referenced and not "GCed"?
> > > 
> > > This has nothing to do with garbage collection.  It's just the way
> > > libgcc avoids having too many source files.  It would be exactly the
> > > same if every function were in its own file.
> > 
> > THe ifdef machinery makes every function to go insto its own .o file
> > which are then archived.  So if user code never calls to fork, the .o
> > file with fork wrapper should not be picked by linker and we should not
> > have link error.
> > 
> > If user code calls fork, then the .o file with wrapper should be picked
> > and we will get linker error on missing fork.  So I think it ought to
> > work as it is now.  Does mingw linker behave somehow differently with
> > archives?  Or is there problem with a libgcov being DLL or something?
> 
> The problem is that the changes to switch to modern C result in calls to
> unprototyped function being an error rather than just warning as before.
> int foo (void) { return fork (); }
> warning: implicit declaration of function ‘fork’ [-Wimplicit-function-declaration]
> previously, now
> error: implicit declaration of function ‘fork’ [-Wimplicit-function-declaration]
> (by default in C99+).
> 
> So, as has been discussed earlier, either we should use __builtin_fork ()
> rather than fork (), or we need in configure to test for fork prototype and
> if missing, prototype it ourselves, or ensure _gcov_fork.o is not compiled
> on targets which don't have fork prototyped.

BTW. The gcc-fedora-mingw buildbot has been broken because of this
issue for the last week:

https://builder.sourceware.org/buildbot/#/builders/gcc-fedora-mingw
../../../gcc/libgcc/libgcov-interface.c: In function '__gcov_fork':
../../../gcc/libgcc/libgcov-interface.c:185:9: error: implicit
declaration of function 'fork' [-Wimplicit-function-declaration]
  185 |   pid = fork ();
      |         ^~~~
make[2]: *** [Makefile:935: _gcov_fork.o] Error 1

Cheers,

Mark