gettimeofday: expose type of second argument

Needed to silence compiler warnings such as:
test-gettimeofday.c:23: warning: initialization from incompatible pointer type
based on whether gettimeofday complies with POSIX or provides
the extension of struct timezone.

* m4/gettimeofday.m4 (gl_FUNC_GETTIMEOFDAY): Do better detection
of glibc extension signature, and define GETTIMEOFDAY_TIMEZONE.
* tests/test-gettimeofday.c: Use it to silence warning.
* doc/posix-functions/gettimeofday.texi (gettimeofday): Document
the issue.

Signed-off-by: Eric Blake <ebb9@byu.net>

ChangeLog

@@ -1,3 +1,12 @@
+2010-02-04  Eric Blake  <ebb9@byu.net>
+
+	gettimeofday: expose type of second argument
+	* m4/gettimeofday.m4 (gl_FUNC_GETTIMEOFDAY): Do better detection
+	of glibc extension signature, and define GETTIMEOFDAY_TIMEZONE.
+	* tests/test-gettimeofday.c: Use it to silence warning.
+	* doc/posix-functions/gettimeofday.texi (gettimeofday): Document
+	the issue.
+
 2010-02-03  Jim Meyering  <meyering@redhat.com>
 
 	regcomp.c: avoid the sole warning from gcc's -Wtype-limits

doc/posix-functions/gettimeofday.texi

@@ -15,6 +15,15 @@ mingw.
 This function is declared with a nonstandard function prototype (only one
 argument, or ``...'' after the first argument) on some platforms.
 @item
+On some platforms, the second argument has type @code{struct
+timezone*} rather than @code{void *}, making it an error to redeclare
+the function with the POSIX signature:
+glibc.
+However, rather than penalize these systems with a replacement
+function, gnulib defines @code{GETTIMEOFDAY_TIMEZONE} to the
+appropriate type for use in avoiding a compiler warning if assigning
+@code{gettimeofday} to a function pointer.
+@item
 On some platforms, @code{gettimeofday} clobbers the buffer in which
 @code{localtime} returns its result:
 MacOS X 10.0.
@@ -22,4 +31,7 @@ MacOS X 10.0.
 
 Portability problems not fixed by Gnulib:
 @itemize
+@item
+Behavior is non-portable if the second argument to @code{gettimeofday}
+is not @code{NULL}.
 @end itemize

m4/gettimeofday.m4

@@ -1,4 +1,4 @@
-# serial 13
+# serial 14
 
 # Copyright (C) 2001-2003, 2005, 2007, 2009-2010 Free Software Foundation, Inc.
 # This file is free software; the Free Software Foundation
@@ -14,30 +14,46 @@ AC_DEFUN([gl_FUNC_GETTIMEOFDAY],
   AC_REQUIRE([gl_HEADER_SYS_TIME_H_DEFAULTS])
   AC_CHECK_FUNCS_ONCE([gettimeofday])
 
-  AC_CACHE_CHECK([for gettimeofday with POSIX signature],
-    [gl_cv_func_gettimeofday_posix_signature],
-    [AC_COMPILE_IFELSE(
-       [AC_LANG_PROGRAM(
-          [[#include <sys/time.h>
-            struct timeval c;
-          ]],
-          [[
-            int (*f) (struct timeval *restrict, void *restrict) = gettimeofday;
-            int x = f (&c, 0);
-            return !(x | c.tv_sec | c.tv_usec);
-          ]])],
-        [gl_cv_func_gettimeofday_posix_signature=yes],
-        [gl_cv_func_gettimeofday_posix_signature=no])])
-
-  gl_FUNC_GETTIMEOFDAY_CLOBBER
-
-  if test $gl_cv_func_gettimeofday_posix_signature != yes; then
-    REPLACE_GETTIMEOFDAY=1
-    if test $gl_cv_func_gettimeofday_clobber != yes; then
+  gl_gettimeofday_timezone=void
+  if test $ac_cv_func_gettimeofday = yes; then
+    gl_FUNC_GETTIMEOFDAY_CLOBBER
+    AC_CACHE_CHECK([for gettimeofday with POSIX signature],
+      [gl_cv_func_gettimeofday_posix_signature],
+      [AC_COMPILE_IFELSE(
+         [AC_LANG_PROGRAM(
+            [[#include <sys/time.h>
+              struct timeval c;
+              int gettimeofday (struct timeval *restrict, void *restrict);
+            ]],
+            [[/* glibc uses struct timezone * rather than the POSIX void *
+                 if _GNU_SOURCE is defined.  However, since the only portable
+                 use of gettimeofday uses NULL as the second parameter, and
+                 since the glibc definition is actually more typesafe, it is
+                 not worth wrapping this to get a compliant signature.  */
+              int (*f) (struct timeval *restrict, void *restrict)
+                = gettimeofday;
+              int x = f (&c, 0);
+              return !(x | c.tv_sec | c.tv_usec);
+            ]])],
+          [gl_cv_func_gettimeofday_posix_signature=yes],
+          [AC_COMPILE_IFELSE(
+            [AC_LANG_PROGRAM(
+              [[#include <sys/time.h>
+int gettimeofday (struct timeval *restrict, struct timezone *restrict);
+              ]])],
+            [gl_cv_func_gettimeofday_posix_signature=almost],
+            [gl_cv_func_gettimeofday_posix_signature=no])])])
+    if test $gl_cv_func_gettimeofday_posix_signature = almost; then
+      gl_gettimeofday_timezone='struct timezone'
+    elif test $gl_cv_func_gettimeofday_posix_signature != yes; then
+      REPLACE_GETTIMEOFDAY=1
       AC_LIBOBJ([gettimeofday])
       gl_PREREQ_GETTIMEOFDAY
     fi
   fi
+  AC_DEFINE_UNQUOTED([GETTIMEOFDAY_TIMEZONE], [$gl_gettimeofday_timezone],
+    [Define this to 'void' or 'struct timezone' to match the system's
+     declaration of the second argument to gettimeofday.])
 ])
 
 

tests/test-gettimeofday.c

@@ -20,7 +20,8 @@
 #include <sys/time.h>
 
 #include "signature.h"
-SIGNATURE_CHECK (gettimeofday, int, (struct timeval *, void *));
+SIGNATURE_CHECK (gettimeofday, int,
+                 (struct timeval *, GETTIMEOFDAY_TIMEZONE *));
 
 #include <time.h>
 
@@ -42,8 +43,5 @@ main (void)
       fprintf (stderr, "gettimeofday still clobbers the localtime buffer!\n");
       return 1;
     }
-  else
-    {
-      return 0;
-    }
+  return 0;
 }