[PATCH] AC_FUNC_VFORK: check for Solaris 2.4 signal-handling bug

[Paul Eggert]

* NEWS:
* doc/autoconf.texi (Particular Functions): Document this.
* lib/autoconf/functions.m4 (_AC_FUNC_VFORK): Check for the bug.
---
 NEWS                      |  7 ++++++-
 doc/autoconf.texi         |  5 +----
 lib/autoconf/functions.m4 | 24 ++++++++++++++++++++----
 3 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/NEWS b/NEWS
index 0fda46e..7c1e77e 100644
--- a/NEWS
+++ b/NEWS
@@ -5,13 +5,18 @@ GNU Autoconf NEWS - User visible changes.
 ** The use of the long-deprecated name 'configure.in' for the autoconf
    input file now elicits a warning in the 'obsolete' category.
 
-** MACROS
+** Macros
 
 - New macro AC_PROG_CC_C11.
 
 - AC_PROG_CC_STDC now prefers C11 if available, falling back on C99
   and then on C89 as before.
 
+- AC_FUNC_VFORK now checks for the signal-handling bug in Solaris 2.4 'vfork'.
+  Formerly, it ignored this bug, so that Emacs could use some tricky
+  code on that platform.  Solaris 2.4 has not been supported since
+  2003 and nowadays it's better to omit that old trick.
+
 * Noteworthy changes in release 2.69 (2012-04-24) [stable]
 
 ** Autoconf now requires perl 5.6 or better (but generated configure
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 7b8bfd5..611b675 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -4993,10 +4993,7 @@ If @file{vfork.h} is found, define @code{HAVE_VFORK_H}.  
If a working
 define @code{vfork} to be @code{fork} for backward compatibility with
 previous versions of @command{autoconf}.  This macro checks for several known
 errors in implementations of @code{vfork} and considers the system to not
-have a working @code{vfork} if it detects any of them.  It is not considered
-to be an implementation error if a child's invocation of @code{signal}
-modifies the parent's signal handler, since child processes rarely change
-their signal handlers.
+have a working @code{vfork} if it detects any of them.
 
 Since this macro defines @code{vfork} only for backward compatibility with
 previous versions of @command{autoconf} you're encouraged to define it
diff --git a/lib/autoconf/functions.m4 b/lib/autoconf/functions.m4
index 5987a0c..782393b 100644
--- a/lib/autoconf/functions.m4
+++ b/lib/autoconf/functions.m4
@@ -1894,10 +1894,18 @@ AC_DEFUN([_AC_FUNC_VFORK],
 [AC_CACHE_CHECK(for working vfork, ac_cv_func_vfork_works,
 [AC_RUN_IFELSE([AC_LANG_SOURCE([[/* Thanks to Paul Eggert for this test.  */
 ]AC_INCLUDES_DEFAULT[
+#include <signal.h>
 #include <sys/wait.h>
 #ifdef HAVE_VFORK_H
 # include <vfork.h>
 #endif
+
+static void
+do_nothing (int sig)
+{
+  (void) sig;
+}
+
 /* On some sparc systems, changes by the child to local and incoming
    argument registers are propagated back to the parent.  The compiler
    is told about this with #include <vfork.h>, but some compilers
@@ -1905,11 +1913,7 @@ AC_DEFUN([_AC_FUNC_VFORK],
    static variable whose address is put into a register that is
    clobbered by the vfork.  */
 static void
-#ifdef __cplusplus
 sparc_address_test (int arg)
-# else
-sparc_address_test (arg) int arg;
-#endif
 {
   static pid_t child;
   if (!child) {
@@ -1934,6 +1938,11 @@ main ()
 
   sparc_address_test (0);
 
+  /* On Solaris 2.4, changes by the child to the signal handler
+     also munge signal handlers in the parent.  To detect this,
+     start by putting the parent's handler in a known state.  */
+  signal (SIGTERM, SIG_DFL);
+
   child = vfork ();
 
   if (child == 0) {
@@ -1955,6 +1964,10 @@ main ()
        || p != p5 || p != p6 || p != p7)
       _exit(1);
 
+    /* Alter the child's signal handler.  */
+    if (signal (SIGTERM, do_nothing) != SIG_DFL)
+      _exit(1);
+
     /* On some systems (e.g. IRIX 3.3), vfork doesn't separate parent
        from child file descriptors.  If the child closes a descriptor
        before it execs or exits, this munges the parent's descriptor
@@ -1970,6 +1983,9 @@ main ()
         /* Was there some problem with vforking?  */
         child < 0
 
+        /* Did the child munge the parent's signal handler?  */
+        || signal (SIGTERM, SIG_DFL) != SIG_DFL
+
         /* Did the child fail?  (This shouldn't happen.)  */
         || status
 
-- 
1.7.11.4