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Fix signal stack namespace (bug 21584)

In POSIX.1:2008, various signal stack symbols - sigaltstack, SS_*,
SIGSTKSZ, MINSIGSTKSZ - are all XSI-shaded.  glibc wrongly makes them
visible for non-XSI POSIX.  This patch fixes the conditionals, leaving
the symbols available for __USE_MISC as it seems likely some of them
are widely used and should be visible by default.  (Note that stack_t
is *not* XSI-shaded and so the conditionals on that are correctly

Tested for x86_64.

2017-06-13  Joseph Myers  <>

	[BZ #21584]
	* signal/signal.h: Make includes of <bits/sigstack.h> and
	<bits/ss_flags.h> conditional on [__USE_XOPEN_EXTENDED ||
	(sigaltstack): Make declaration conditional on

diff --git a/signal/signal.h b/signal/signal.h
index 23cd8ef..8dfe849 100644
--- a/signal/signal.h
+++ b/signal/signal.h
@@ -301,20 +301,22 @@ extern int sigreturn (struct sigcontext *__scp) __THROW;
    calls be restarted after signal SIG.  */
 extern int siginterrupt (int __sig, int __interrupt) __THROW;
-# include <bits/sigstack.h>
 # include <bits/types/stack_t.h>
-# include <bits/ss_flags.h>
 # if defined __USE_XOPEN || defined __USE_XOPEN2K8
 /* This will define `ucontext_t' and `mcontext_t'.  */
 #  include <sys/ucontext.h>
 # endif
+#endif /* Use POSIX.1-2008 or X/Open Unix.  */
+#if defined __USE_XOPEN_EXTENDED || defined __USE_MISC
+# include <bits/sigstack.h>
+# include <bits/ss_flags.h>
 /* Alternate signal handler stack interface.
    This interface should always be preferred over `sigstack'.  */
 extern int sigaltstack (const stack_t *__restrict __ss,
 			stack_t *__restrict __oss) __THROW;
-#endif /* Use POSIX.1-2008 or X/Open Unix.  */
+#endif /* __USE_XOPEN_EXTENDED || __USE_MISC */
 #if ((defined __USE_XOPEN_EXTENDED && !defined __USE_XOPEN2K8)	\
      || defined __USE_MISC)

Joseph S. Myers

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