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Subject[PATCH] Fix BUILD_BUG_ON in fs/compat_ioctl.c to build with gcc 4.5 snapshot
Fix BUILD_BUG_ON in fs/compat_ioctl.c to build with gcc 4.5 snapshot

The BUILD_BUG_ON in compat_ioctl_check_table() fails
with a recent gcc mainline snapshot (gcc version 4.5.0 20091219)
(GCC)), even though it works with older compilers.

const int max = ARRAY_SIZE(ioctl_pointer) - 1;
BUILD_BUG_ON(max >= (1 << 16));

I replaced the BUILD_BUG_ON with a old style extern reference and
that works.

That shows that the actual expression is evaluated ok and something must be
wrong with the BUILD_BUG_ON macro itself. Maybe Rusty's rework
will fix that (I haven't tried but it's probably worth investigating)

I filed a bug on the compiler too
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42439

According to Joseph Myers the problem is that even when declared
with const "max" is not a constant expression in the C standard sense,
so the code is indeed incorrect.

Anyways with this workaround a relatively standard defconfig like
configuration and a 64bit allyes configuration builds again with gcc 4.5

Cc: jbeulich@novell.com
Cc: rusty@rustcorp.com.au
Cc: rguenther@suse.de

Signed-off-by: Andi Kleen <ak@linux.intel.com>

---
fs/compat_ioctl.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

Index: linux-2.6.33-rc1-ak/fs/compat_ioctl.c
===================================================================
--- linux-2.6.33-rc1-ak.orig/fs/compat_ioctl.c
+++ linux-2.6.33-rc1-ak/fs/compat_ioctl.c
@@ -1649,8 +1649,10 @@ static int compat_ioctl_check_table(unsi
{
int i;
const int max = ARRAY_SIZE(ioctl_pointer) - 1;
+ extern void __ioctl_pointer_too_large(void);

- BUILD_BUG_ON(max >= (1 << 16));
+ if (max >= (1 << 16))
+ __ioctl_pointer_too_large();

/* guess initial offset into table, assuming a
normalized distribution */

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