AC_HEADER_MAJOR vs. glibc 2.25(-to-be)
Eric Blake
eblake@redhat.com
Tue Sep 13 22:31:00 GMT 2016
[adding libvirt list, as this is what sparked my investigations so far
today]
On 09/13/2016 04:36 PM, Eric Blake wrote:
> One other possibility that distros can do is to prime a config.site
> file, with $ac_cv_header_sys_types_h_makedev=no, to forcefully bypass
> the configure check that is normally done where <sys/types.h> would
> warn. It has to be in config.site, because non-glibc systems do not
> want to do that.
Okay, I have confirmed that this prime-the-cache idea DOES work, using
libvirt.git commit 419bc8cf (one commit prior to d53fa838 which
installed a hack into libvirt to force the use of -Werror for the
duration of AC_HEADER_MAJOR [1]). By itself, './configure' succeeds but
leaves MAJOR_IN_SYSMACROS undefined, which results in a build failure
later in libvirt; but when run as './configure
ac_cv_header_sys_types_h_makedev=no', MAJOR_IN_SYSMACROS gets defined
and the build succeeds.
I want to remove the libvirt hack (not all compilers understand -Werror,
even if libvirt is only ever built by gcc or clang), and my experiment
was enough to prove that:
1. distros that provide a config.site file can use this file to avoid
the problem, even for packages that have not yet rebuilt with a
new-enough autoconf to fix the issue
2. autoconf and gnulib should indeed be fixed to probe for
<sys/sysmacros.h> _prior_ to probing for whether makedev() exists in
<sys/type.h>, rather than the 2.69 logic of only checking for
<sys/sysmacros.h> if makedev() was not found earlier.
Of course, the libvirt hack should not be reverted until autoconf and
gnulib have the final solution in place.
>
> Meanwhile, even without an autoconf release scheduled, I am currently
> working on patching the existing autoconf macro and documentation to
> match the current situation. It sounds to me like we want the following
> logic:
>
> If <sys/sysmacros.h> exists and defines major(), use that,
> else if <sys/mkdev.h> exists, use that,
> else if <sys/types.h> defines major(), use that,
> else not available
The current autoconf code assumes that if <sys/sysmacros.h> exists, then
it defines major()/minor()/makedev(); I think that assumption is still
safe. Where autoconf was wrong was that it was not even probing for the
existence of <sys/sysmacros.h> if it found that <sys/types.h> was enough
to pollute the namespace with the three macros.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 604 bytes
Desc: OpenPGP digital signature
URL: <http://sourceware.org/pipermail/libc-alpha/attachments/20160913/da499088/attachment.sig>
More information about the Libc-alpha
mailing list