PowerPC SIGSTKSZ

[Alan Modra <amodra at gmail dot com>]

This copies the sparc version of sigstack.h, which gives powerpc
#define MINSIGSTKSZ     4096
#define SIGSTKSZ        16384

Before the VSX changes, struct rt_sigframe size was 1920 plus 128 for
__SIGNAL_FRAMESIZE giving ppc64 exactly the default MINSIGSTKSZ of
2048.

After VSX, ucontext increased by 256 bytes.  Oops, we're over
MINSIGSTKSZ, so powerpc has been using the wrong value for quite a
while.  Add another ucontext for TM and rt_sigframe is now at 3872,
giving actual MINSIGSTKSZ of 4000.

The glibc testcase that I was looking at was tst-cancel21, which
allocates 2*SIGSTKSZ (not because the test is trying to be
conservative, but because the test actually has nested signal stack
frames).  We blew the allocation by 48 bytes when using current
mainline gcc to compile glibc (le ppc64).

The required stack depth in _dl_lookup_symbol_x from the top of the
next signal frame was 10944 bytes.  I guess you'd want to add 288 to
that, implying an actual SIGSTKSZ of 11232.

	* sysdeps/unix/sysv/linux/powerpc/bits/sigstack.h: New file.

diff --git a/sysdeps/unix/sysv/linux/powerpc/bits/sigstack.h b/sysdeps/unix/sysv/linux/powerpc/bits/sigstack.h
new file mode 100644
index 0000000..33be9e8
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/powerpc/bits/sigstack.h
@@ -0,0 +1,54 @@
+/* sigstack, sigaltstack definitions.
+   Copyright (C) 1998-2013 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _SIGNAL_H
+# error "Never include this file directly.  Use <signal.h> instead"
+#endif
+
+
+/* Structure describing a signal stack (obsolete).  */
+struct sigstack
+  {
+    void *ss_sp;		/* Signal stack pointer.  */
+    int ss_onstack;		/* Nonzero if executing on this stack.  */
+  };
+
+
+/* Possible values for `ss_flags.'.  */
+enum
+{
+  SS_ONSTACK = 1,
+#define SS_ONSTACK	SS_ONSTACK
+  SS_DISABLE
+#define SS_DISABLE	SS_DISABLE
+};
+
+/* Minimum stack size for a signal handler.  */
+#define MINSIGSTKSZ	4096
+
+/* System default stack size.  */
+#define SIGSTKSZ	16384
+
+
+/* Alternate, preferred interface.  */
+typedef struct sigaltstack
+  {
+    void *ss_sp;
+    int ss_flags;
+    size_t ss_size;
+  } stack_t;

-- 
Alan Modra
Australia Development Lab, IBM