Build problem with latest GCC (auto-load.c fails to compile)

Build problem with latest GCC (auto-load.c fails to compile)

[Steve Ellcey]

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Has anyone tried building gdb with the latest (top-of-tree) GCC sources?
I just did that and the build died with message shown below.

Steve Ellcey
sellcey@caviumnetworks.com



../../../src/binutils-gdb/gdb/auto-load.c: In function ‘void print_scripts(VEC_loaded_script_ptr*)’:
../../../src/binutils-gdb/gdb/auto-load.c:1317:52: error: argument 1 null where non-null expected [-Werror=nonnull]
   sizeof (loaded_script_ptr), sort_scripts_by_name);
                                                    ^
In file included from /home/ubuntu/sellcey/test-ifunc/install-init/include/c++/7.0.0/cstdlib:75:0,
                 from /home/ubuntu/sellcey/test-ifunc/install-init/include/c++/7.0.0/stdlib.h:36,
                 from build-gnulib/import/stdlib.h:36,
                 from ../../../src/binutils-gdb/gdb/common/common-defs.h:53,
                 from ../../../src/binutils-gdb/gdb/defs.h:28,
                 from ../../../src/binutils-gdb/gdb/auto-load.c:20:
/usr/include/stdlib.h:764:13: note: in a call to function ‘void qsort(void*, size_t, size_t, __compar_fn_t)’ declared here
 extern void qsort (void *__base, size_t __nmemb, size_t __size,
             ^~~~~
cc1plus: all warnings being treated as errors
Makefile:1880: recipe for target 'auto-load.o' failed
make[2]: *** [auto-load.o] Error 1
make[2]: Leaving directory '/home/ubuntu/sellcey/test-ifunc/obj/binutils-gdb/gdb'
Makefile:10455: recipe for target 'all-gdb' failed
make[1]: *** [all-gdb] Error 2
make[1]: Leaving directory '/home/ubuntu/sellcey/test-ifunc/obj/binutils-gdb'
Makefile:850: recipe for target 'all' failed
make: *** [all] Error 2

Re: Build problem with latest GCC (auto-load.c fails to compile)

[Pedro Alves]

On 12/21/2016 09:15 PM, Steve Ellcey wrote:
> Has anyone tried building gdb with the latest (top-of-tree) GCC sources?
> I just did that and the build died with message shown below.

I don't see the warning/error here, with ToT GCC.

> 
> 
> 
> ../../../src/binutils-gdb/gdb/auto-load.c: In function ‘void print_scripts(VEC_loaded_script_ptr*)’:
> ../../../src/binutils-gdb/gdb/auto-load.c:1317:52: error: argument 1 null where non-null expected [-Werror=nonnull]
>    sizeof (loaded_script_ptr), sort_scripts_by_name);
>                                                     ^


That's:

static void
print_scripts (VEC (loaded_script_ptr) *scripts)
{
  int i;
  loaded_script_ptr script;

  qsort (VEC_address (loaded_script_ptr, scripts),
	 VEC_length (loaded_script_ptr, scripts),
	 sizeof (loaded_script_ptr), sort_scripts_by_name);
  for (i = 0; VEC_iterate (loaded_script_ptr, scripts, i, script); ++i)
    print_script (script);
}

By design, a NULL VEC pointer is an empty VEC (though empty VECs can
be non-NULL if memory has already been reserved).  And VEC_address
returns NULL on such NULL VECs.

So sounds like GCC thinks that "scripts" here may be NULL
somehow?    I'm not immediately seeing how, given:

  script_files = VEC_alloc (loaded_script_ptr, 10);
  script_texts = VEC_alloc (loaded_script_ptr, 10);

Might be a GCC bug.  There's ongoing discussion on the gcc-patches
list about these -Wnonnull warnings.

Calling qsort with a null base is undefined, even if nmemb is 0.  So
fix could be simply to skip the qsort if the VEC is
empty (or len <= 1, since it's pointless to sort one element), like
we do in other places.  Something like:

static void
print_scripts (VEC (loaded_script_ptr) *scripts)
{
  int i;
  loaded_script_ptr script;

  if (VEC_length (int, ids) > 1)
    qsort (VEC_address (loaded_script_ptr, scripts),
	 VEC_length (loaded_script_ptr, scripts),
	 sizeof (loaded_script_ptr), sort_scripts_by_name);
  for (i = 0; VEC_iterate (loaded_script_ptr, scripts, i, script); ++i)
    print_script (script);
}

Thanks,
Pedro Alves

Re: Build problem with latest GCC (auto-load.c fails to compile)

[Steve Ellcey]

On Thu, 2016-12-22 at 16:04 +0000, Pedro Alves wrote:
> On 12/21/2016 09:15 PM, Steve Ellcey wrote:
> > 
> > Has anyone tried building gdb with the latest (top-of-tree) GCC
> > sources?
> > I just did that and the build died with message shown below.
> I don't see the warning/error here, with ToT GCC.

I don't get it anymore either.  I think this was a bogus warning and it
was fixed in GCC with the patch for GCC bug 78817.

Steve Ellcey
sellcey@caviumnetworks.com