Fix sigstack namespace (bug 21511).

The sigstack function was removed in the 2001 edition of POSIX, and
the sigstack structure in the 2008 edition.  signal.h wrongly includes
those declarations even for newer POSIX versions.  This patch fixes
the conditions, and conform/ expectations, accordingly.

This patch makes the minimum change to when these declarations are
present, leaving them visible for __USE_MISC as they would previously
have been visible by default.  Arguably these legacy declarations
should only be visible when an old standard is specifically requested,
but implementing that would require arranging for the various sigstack
implementations to be able to see the struct sigstack type despite it
not being in _GNU_SOURCE in that case.

Tested for x86_64.

	[BZ #21511]
	* signal/signal.h: Include <bits/types/struct_sigstack.h> only if
	[(__USE_XOPEN_EXTENDED && !__USE_XOPEN2K8) || __USE_MISC].
	(sigstack): Declare only if [(__USE_XOPEN_EXTENDED &&
	!__USE_XOPEN2K) || __USE_MISC].
	* conform/data/signal.h-data (struct sigstack): Expect type only
	if [!XOPEN2K8 && !POSIX2008].
	(sigstack): Expect function only if [XPG42 || UNIX98].

3 files changed, 26 insertions, 8 deletions

diff --git a/ChangeLog b/ChangeLog
index 85722c8f86..865c7e9960 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,14 @@
 2017-05-23  Joseph Myers  <joseph@codesourcery.com>
 
+	[BZ #21511]
+	* signal/signal.h: Include <bits/types/struct_sigstack.h> only if
+	[(__USE_XOPEN_EXTENDED && !__USE_XOPEN2K8) || __USE_MISC].
+	(sigstack): Declare only if [(__USE_XOPEN_EXTENDED &&
+	!__USE_XOPEN2K) || __USE_MISC].
+	* conform/data/signal.h-data (struct sigstack): Expect type only
+	if [!XOPEN2K8 && !POSIX2008].
+	(sigstack): Expect function only if [XPG42 || UNIX98].
+
 	[BZ #21457]
 	* sysdeps/arm/sys/ucontext.h: Do not include <signal.h>,
 	<bits/sigstack.h>, <bits/types/struct_sigstack.h> or
diff --git a/conform/data/signal.h-data b/conform/data/signal.h-data
index 3651e86ae1..8fbe3ac55d 100644
--- a/conform/data/signal.h-data
+++ b/conform/data/signal.h-data
@@ -141,10 +141,12 @@ element stack_t {void*} ss_sp
 element stack_t size_t ss_size
 element stack_t int ss_flags
 
+#  if !defined XOPEN2K8 && !defined POSIX2008
 type {struct sigstack}
 
 element {struct sigstack} int ss_onstack
 element {struct sigstack} {void*} ss_sp
+#  endif
 # endif
 
 # ifndef XPG4
@@ -249,7 +251,7 @@ function int sigqueue (pid_t, int, const union sigval)
 function int sigrelse (int)
 function void (*sigset (int, void(*)(int)))(int)
 # endif
-# if !defined POSIX
+# if defined XPG42 || defined UNIX98
 function int sigstack (struct sigstack*, struct sigstack*)
 # endif
 function int sigsuspend (const sigset_t*)
diff --git a/signal/signal.h b/signal/signal.h
index a51e912d08..947873ea8e 100644
--- a/signal/signal.h
+++ b/signal/signal.h
@@ -297,7 +297,6 @@ extern int sigreturn (struct sigcontext *__scp) __THROW;
 extern int siginterrupt (int __sig, int __interrupt) __THROW;
 
 # include <bits/sigstack.h>
-# include <bits/types/struct_sigstack.h>
 # include <bits/types/stack_t.h>
 # include <bits/ss_flags.h>
 # if defined __USE_XOPEN || defined __USE_XOPEN2K8
@@ -305,12 +304,6 @@ extern int siginterrupt (int __sig, int __interrupt) __THROW;
 #  include <sys/ucontext.h>
 # endif
 
-/* Run signals handlers on the stack specified by SS (if not NULL).
-   If OSS is not NULL, it is filled in with the old signal stack status.
-   This interface is obsolete and on many platform not implemented.  */
-extern int sigstack (struct sigstack *__ss, struct sigstack *__oss)
-     __THROW __attribute_deprecated__;
-
 /* Alternate signal handler stack interface.
    This interface should always be preferred over `sigstack'.  */
 extern int sigaltstack (const struct sigaltstack *__restrict __ss,
@@ -318,6 +311,20 @@ extern int sigaltstack (const struct sigaltstack *__restrict __ss,
 
 #endif /* Use POSIX.1-2008 or X/Open Unix.  */
 
+#if ((defined __USE_XOPEN_EXTENDED && !defined __USE_XOPEN2K8)	\
+     || defined __USE_MISC)
+# include <bits/types/struct_sigstack.h>
+#endif
+
+#if ((defined __USE_XOPEN_EXTENDED && !defined __USE_XOPEN2K)	\
+     || defined __USE_MISC)
+/* Run signals handlers on the stack specified by SS (if not NULL).
+   If OSS is not NULL, it is filled in with the old signal stack status.
+   This interface is obsolete and on many platform not implemented.  */
+extern int sigstack (struct sigstack *__ss, struct sigstack *__oss)
+     __THROW __attribute_deprecated__;
+#endif
+
 #ifdef __USE_XOPEN_EXTENDED
 /* Simplified interface for signal management.  */