question on sparc SHMLBA helper function

[David Miller <davem at davemloft dot net>]

I'm trying to fix a sparc glibc bug in that we use the wrong value for
SHMLBA (this is BZ #6471), currently it's PAGE_SIZE but it needs to be
a value which is dependent upon the CPU.

Some of these cases aren't easy to compute, but the main problem I
have is figuring out where to put the helper function.

Basically I have a __getshmlba that gets added as a sysdep routine
when subdir==sysvipc on sparc.

But the issue is where do I put the declaration so we can have a
hidden symbol available for things like shmat.c that reference SHMLBA
inside of glibc?

I considered putting something like:

extern int __getshmlba (void) __attribute__ ((__const__));
libc_hidden_proto (__getshmlba)

in include/unistd.h since that's where __getpagesize is right now, but
I'm not so sure about putting a sparc specific interface there.

Any suggestions?  Here's the patch I have so far.

--------------------
[PATCH] Try to fix sparc SHMLBA bug.

---
 sysdeps/unix/sysv/linux/sparc/Makefile    |    4 +++
 sysdeps/unix/sysv/linux/sparc/bits/shm.h  |    4 +-
 sysdeps/unix/sysv/linux/sparc/getshmlba.c |   40 +++++++++++++++++++++++++++++
 3 files changed, 46 insertions(+), 2 deletions(-)
 create mode 100644 sysdeps/unix/sysv/linux/sparc/getshmlba.c

diff --git a/sysdeps/unix/sysv/linux/sparc/Makefile b/sysdeps/unix/sysv/linux/sparc/Makefile
index 96bf0bb..d769c48 100644
--- a/sysdeps/unix/sysv/linux/sparc/Makefile
+++ b/sysdeps/unix/sysv/linux/sparc/Makefile
@@ -7,3 +7,7 @@ syscall-list-64bit-condition := __WORDSIZE == 64
 ifeq ($(subdir),rt)
 librt-routines += rt-sysdep
 endif
+
+ifeq ($(subdir),sysvipc)
+sysdep_routines += getshmlba
+endif
diff --git a/sysdeps/unix/sysv/linux/sparc/bits/shm.h b/sysdeps/unix/sysv/linux/sparc/bits/shm.h
index b0966d6..eb530de 100644
--- a/sysdeps/unix/sysv/linux/sparc/bits/shm.h
+++ b/sysdeps/unix/sysv/linux/sparc/bits/shm.h
@@ -40,8 +40,8 @@
 __BEGIN_DECLS
 
 /* Segment low boundary address multiple.  */
-#define SHMLBA		(__getpagesize ())
-extern int __getpagesize (void) __THROW __attribute__ ((__const__));
+#define SHMLBA		(__getshmlba ())
+extern int __getshmlba (void) __attribute__ ((__const__));
 
 
 /* Type to count number of attaches.  */
diff --git a/sysdeps/unix/sysv/linux/sparc/getshmlba.c b/sysdeps/unix/sysv/linux/sparc/getshmlba.c
new file mode 100644
index 0000000..b39fffa
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/sparc/getshmlba.c
@@ -0,0 +1,40 @@
+/* Copyright (C) 2012
+   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/>.  */
+
+#include <unistd.h>
+#include <sys/shm.h>
+#include <ldsodefs.h>
+
+int
+__getshmlba(void)
+{
+  uint64_t hwcap = GLRO(dl_hwcap);
+  int pgsz = GLRO(dl_pagesize);
+
+  if (hwcap & HWCAP_SPARC_V9)
+    {
+      if (pgsz < (16 * 1024))
+	return 16 * 1024;
+      else
+	return pgsz;
+    }
+  else if (!(hwcap & HWCAP_SPARC_FLUSH))
+    return 64 * 1024;
+  else
+    return 256 * 1024;
+}
-- 
1.7.6.401.g6a319