svn commit: r311929 - head/sys/boot/common

[Dimitry Andric]

On 11 Jan 2017, at 22:42, Ian Lepore <ian at FreeBSD.org> wrote:
> 
> On Wed, 2017-01-11 at 13:35 -0800, Ngie Cooper wrote:
>> On Wed, Jan 11, 2017 at 10:47 AM, Dimitry Andric <dim at freebsd.org>
>> wrote:
>>> 
>>> Author: dim
>>> Date: Wed Jan 11 18:47:00 2017
>>> New Revision: 311929
>>> URL: https://svnweb.freebsd.org/changeset/base/311929
>>> 
>>> Log:
>>>   Don't include <errno.h> in reloc_elf.c, as it includes <stand.h>
>>> just
>>>   after it, which has a conflicting definition of errno.  This
>>> leads to
>>>   the following warning with clang 4.0.0:
>>> 
>>>       In file included from sys/boot/common/reloc_elf32.c:6:
>>>       In file included from sys/boot/common/reloc_elf.c:37:
>>>       /usr/obj/usr/src/tmp/usr/include/stand.h:155:12: error: this
>>> function declaration is not a prototype [-Werror,-Wstrict-
>>> prototypes]
>>>       extern int errno;
>>>                  ^
>>>       sys/sys/errno.h:46:26: note: expanded from macro 'errno'
>>>       #define errno           (* __error())
>> It seems like libstand (once again) should be fixed, not the
>> "offending code".
>> -Ngie
>> 
> 
> In this case it's not the library that's in error.  Libstand is the
> thing that implements errno, so it's the thing that must define it.
> 
> The code that includes both errno.h and libstand.h was wrong.  errno.h
> is a standard header file used with libc, and the loader code doesn't
> link with libc.
> 
> The thing that amazes me is the usual:  how did this ever work with gcc
> 4.2?

The line:

    extern int errno;

expanded to:

    extern int (* __error());

which is a declaration of an external function pointer called __error
(albeit with an empty parameter list).  Since nobody actually refers to
this symbol in libstand, there are no later complaints.

Interestingly, reloc_elf.c does not use errno at all, so I have no idea
why the include was originally added.

-Dimitry

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