Fix struct sigaltstack namespace (bug 21517).

glibc defines the stack_t type with the tag struct sigaltstack.  This
is not permitted by POSIX; sigaltstack is only reserved with file
scope in the namespace of ordinary identifiers, not the tag namespace,
and in the case where stack_t is obtained from ucontext.h rather than
signal.h, it's not reserved with file scope at all.

This patch removes the tag accordingly and updates uses in glibc of
struct sigaltstack.  This is similar to the removal of the "struct
siginfo" tag a few years ago: C++ name mangling changes are an
unavoidable consequence.  A NEWS item is added to note the changed
mangling.  There is inevitably some risk of breaking builds of
anything that relies on the struct sigaltstack name (though the first
few hits I looked at from codesearch.debian.net generally seemed to
involve code that could use the stack_t name conditionally, so
depending on how they determine the conditionals they may work with
glibc not defining the struct tag anyway).

Tested for x86_64 and x86, and with build-many-glibcs.py.

	[BZ #21517]
	* bits/types/stack_t.h (stack_t): Remove struct tag.
	* sysdeps/unix/sysv/linux/bits/types/stack_t.h (stack_t):
	Likewise.
	* sysdeps/unix/sysv/linux/mips/bits/types/stack_t.h (stack_t):
	Likewise.
	* debug/segfault.c (install_handler): Use stack_t instead of
	struct sigaltstack.
	* hurd/hurd/signal.h (struct hurd_sigstate): Likewise.
	* hurd/trampoline.c (_hurd_setup_sighandler): Likewise.
	* include/signal.h (__sigaltstack): Likwise.
	* signal/sigaltstack.c (__sigaltstack): Likewise.
	* signal/signal.h (sigaltstack): Likewise.
	* sysdeps/mach/hurd/i386/signal-defines.sym
	(SIGALTSTACK__SS_SP__OFFSET): Likewise.
	(SIGALTSTACK__SS_SIZE__OFFSET): Likewise.
	(SIGALTSTACK__SS_FLAGS__OFFSET): Likewise.
	* sysdeps/mach/hurd/sigaltstack.c (__sigaltstack): Likewise.
	* sysdeps/mach/hurd/sigstack.c (sigstack): Likewise.
	* sysdeps/unix/sysv/linux/alpha/sys/procfs.h (struct
	elf_prstatus): Likewise.
	* sysdeps/unix/sysv/linux/hppa/____longjmp_chk.c (CHECK_SP):
	Likewise.
	* sysdeps/unix/sysv/linux/ia64/sys/procfs.h (struct elf_prstatus):
	Likewise.
	* sysdeps/unix/sysv/linux/m68k/____longjmp_chk.c (CHECK_SP):
	Likewise.
	* sysdeps/unix/sysv/linux/powerpc/sys/procfs.h (struct
	elf_prstatus): Likewise.
	* sysdeps/unix/sysv/linux/sh/sys/procfs.h (struct elf_prstatus):
	Likewise.
	* sysdeps/unix/sysv/linux/sys/procfs.h (struct elf_prstatus):
	Likewise.

2 files changed, 3 insertions, 3 deletions

diff --git a/signal/sigaltstack.c b/signal/sigaltstack.c
index e4d23195a0..b70afa7127 100644
--- a/signal/sigaltstack.c
+++ b/signal/sigaltstack.c
@@ -21,7 +21,7 @@
 /* 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.  */
 int
-sigaltstack (const struct sigaltstack *ss, struct sigaltstack *oss)
+sigaltstack (const stack_t *ss, stack_t *oss)
 {
   __set_errno (ENOSYS);
   return -1;
diff --git a/signal/signal.h b/signal/signal.h
index 21d628dbd2..b3114736a5 100644
--- a/signal/signal.h
+++ b/signal/signal.h
@@ -309,8 +309,8 @@ extern int siginterrupt (int __sig, int __interrupt) __THROW;
 
 /* Alternate signal handler stack interface.
    This interface should always be preferred over `sigstack'.  */
-extern int sigaltstack (const struct sigaltstack *__restrict __ss,
-			struct sigaltstack *__restrict __oss) __THROW;
+extern int sigaltstack (const stack_t *__restrict __ss,
+			stack_t *__restrict __oss) __THROW;
 
 #endif /* Use POSIX.1-2008 or X/Open Unix.  */