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Re: [libvirt] [PATCH v2] virsh: workaround readline prototypes warnings

On Thu, Jun 08, 2017 at 05:20:35PM +0400, Roman Bogorodskiy wrote:
 Ján Tomko wrote:

On Fri, Jun 02, 2017 at 07:04:23PM +0400, Roman Bogorodskiy wrote:
>When building with clang 4.0.0, virsh build fails like this:


>Bug report on the readline mailing list:
> http://lists.gnu.org/archive/html/bug-readline/2017-05/msg00004.html
> configure.ac        | 2 +-
> m4/virt-readline.m4 | 4 +++-
> tools/Makefile.am   | 3 ++-
> 3 files changed, 6 insertions(+), 3 deletions(-)
>diff --git a/configure.ac b/configure.ac
>index 1af5538ee..1a73b3466 100644
>--- a/configure.ac
>+++ b/configure.ac
>@@ -328,7 +328,7 @@ dnl Availability of various common headers (non-fatal if missing).
> AC_CHECK_HEADERS([pwd.h regex.h sys/un.h \
>   sys/poll.h syslog.h mntent.h net/ethernet.h linux/magic.h \
>   sys/un.h sys/syscall.h sys/sysctl.h netinet/tcp.h ifaddrs.h \
>-  libtasn1.h sys/ucred.h sys/mount.h])
>+  libtasn1.h sys/ucred.h sys/mount.h stdarg.h])
> dnl Check whether endian provides handy macros.
> AC_CHECK_DECLS([htole64], [], [], [[#include <endian.h>]])
> AC_CHECK_FUNCS([stat stat64 __xstat __xstat64 lstat lstat64 __lxstat __lxstat64])

What is the purpose of checking for stdarg.h?

As the commit message says: "... and add a check for stdarg.h so readline headers
use proper rl_message declaration." I thought that's enough details, but
obviously it's not as you're asking :-)

I skipped that part of the commit message. I did not expect that other
checks would be influenced by this AC_CHECK_HEADERS.

The thing is that there's a following code in readline.h:

#if defined (USE_VARARGS) && defined (PREFER_STDARG)
extern int rl_message (const char *, ...)  __attribute__((__format__ (printf, 1, 2)));
extern int rl_message ();

The latter generates the described warning and the former does not.

PREFER_STDARG and USE_VARARGS come from another readline header,
rlstdc.h, and it contains the following:

#if defined (__STDC__) && defined (HAVE_STDARG_H)
#  define USE_VARARGS
#  if defined (HAVE_VARARGS_H)
#    define PREFER_VARARGS
#    define USE_VARARGS
#  endif

So we need to have HAVE_STDARG_H defined to have a proper declaration.

How do you like if I rephrase it like "... and add a check for stdarg.h so
we have HAVE_STDARG_H defined that's needed by the readline headers to use
proper rl_message declaration"?

Yes, that is clear enough even for me :)


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