[Bug c/42439] New: Linux kernel BUILD_BUG_ON() broke

["andi-gcc at firstfloor dot org" <gcc-bugzilla at gcc dot gnu dot org>]

The linux kernel uses a special macro BUILD_BUG_ON() that uses
some tricks using bitfields to evaluate constant expressions at compile time
and error out if they are violated.

One of the BUILD_BUG_ON()s in a recent kernel now fail with gcc 4.5 snapshot
(gcc version 4.5.0 20091219 (experimental) (GCC)),
when 4.4 and earlier work.

The actual expression is evaluated correctly (I replaced it with a different
form and that worked) 

I'll be submitting a workaround to the kernel, but it might be some 
sort of regression.

I'm attaching the preprocessed file

% gcc44 fs/compat_ioctl.i -O2 -c           (as expected)
% gcc45 fs/compat_ioctl.i -O2 -c
linux-2.6.33-rc1-ak/fs/compat_ioctl.c: In function 'compat_ioctl_check_table':
linux-2.6.33-rc1-ak/fs/compat_ioctl.c:1653:24: error: bit-field '<anonymous>'
width not an integer constant

(fails)


-- 
           Summary: Linux kernel BUILD_BUG_ON() broke
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: andi-gcc at firstfloor dot org
 GCC build triplet: x86_64-linux
  GCC host triplet: x86_64-linux
GCC target triplet: x86_64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42439