Messages in this thread Patch in this message | | | Date | Sun, 20 Dec 2009 17:53:15 +0100 | From | Andi Kleen <> | Subject | [PATCH] Fix BUILD_BUG_ON in fs/compat_ioctl.c to build with gcc 4.5 snapshot |
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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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