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Date: Thu, 30 May 2013 22:03:44 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: bug in <sys/un.h>
Message-ID: <20130530200344.GA23141@calimero.vinschen.de>
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References: <51A78E70 DOT 1010600 AT redhat DOT com>
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User-Agent: Mutt/1.5.21 (2010-09-15)

On May 30 11:37, Eric Blake wrote:
> STC - this program does nothing useful when executed; it merely exists
> to show a compilation problem extracted from a larger program:
> 
> $ cat foo.c
> #ifdef WORKAROUND
> # include <sys/socket.h>
> #endif
> #include <sys/un.h>
> #include <sys/socket.h>
> int main(void) {
>   const struct msghdr msg;
>   return sendmsg(0, &msg, 0);
> }
> $ gcc -o foo -Wall foo.c
> foo.c: In function 'main':
> foo.c:9:5: warning: passing argument 2 of 'sendmsg' from incompatible
> pointer type
> /usr/include/sys/socket.h:42:11: note: expected 'const struct msghdr *'
> but argument is of type 'const struct msghdr *'
> $ gcc -o foo -Wall foo.c -DWORKAROUND
> $
> 
> Gcc has a less-than-stellar error message (expect type X but have type
> X); it could do a better job about pointing out that it is complaining
> about two different 'type X' declarations, and where they come from.
> But the root cause is that if <sys/un.h> is included first, then the use
> of 'struct msghdr' applied in the declaration of sendmsg() is somehow
> scoped incorrectly (local to the declaration rather than the global
> type), so that the compiler really is complaining about two different
> incompatible 'struct msghdr' layouts.  I'm not quite sure what the fix
> should be, [...]

Try this:

Index: cygwin/if.h
===================================================================
RCS file: /cvs/src/src/winsup/cygwin/include/cygwin/if.h,v
retrieving revision 1.11
diff -u -p -r1.11 if.h
--- cygwin/if.h	21 Jan 2013 04:38:30 -0000	1.11
+++ cygwin/if.h	30 May 2013 20:02:56 -0000
@@ -16,7 +16,7 @@ extern "C" {
 #endif /* __cplusplus */
 
 #include <sys/types.h>
-#include <sys/socket.h>
+#include <cygwin/socket.h>
 
 /* Standard interface flags. */
 #define IFF_UP           0x1             /* interface is up               */


It resolves a circular dependency problem in the header files.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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