On Tue, Nov 24 2015, Andy Shevchenko <[email protected]> wrote:
> On Mon, Nov 23, 2015 at 11:29 PM, Rasmus Villemoes > <[email protected]> wrote: >> 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. > > And any objections to put it into vsnprintf() ? I'd like to keep it close to the type definition. And I was hoping someone would come forward and say "yeah, that's been bugging me too, here's a patch I've been sitting on to fix that". Almost every compiler released this decade has _Static_assert, it's about time we start using that instead of the current mess of homegrown workarounds... Rasmus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
