lib/vsprintf.c: expand field_width to 24 bits

Maurizio Lombardi reported a problem [1] with the %pb extension: It
doesn't work for sufficiently large bitmaps, since the size is stashed
in the field_width field of the struct printf_spec, which is currently
an s16.  Concretely, this manifested itself in
/sys/bus/pseudo/drivers/scsi_debug/map being empty, since the bitmap
printer got a size of 0, which is the 16 bit truncation of the actual
bitmap size.

We do want to keep struct printf_spec at 8 bytes so that it can cheaply
be passed by value.  The qualifier field is only used for internal
bookkeeping in format_decode, so we might as well use a local variable
for that.  This gives us an additional 8 bits, which we can then use for
the field width.

To stay in 8 bytes, we need to do a little rearranging and make the type
member a bitfield as well.  For consistency, change all the members to
bit fields.  gcc doesn't generate much worse code with these changes (in
fact, bloat-o-meter says we save 300 bytes - which I think is a little
surprising).

I didn't find a BUILD_BUG/compiletime_assertion/... which would work
outside function context, so for now I just open-coded it.

[1] http://thread.gmane.org/gmane.linux.kernel/2034835

[[email protected]: avoid open-coded BUILD_BUG_ON]
Signed-off-by: Rasmus Villemoes <[email protected]>
Reported-by: Maurizio Lombardi <[email protected]>
Acked-by: Tejun Heo <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Joe Perches <[email protected]>
Cc: Kees Cook <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions