enabling libgcc for 64-bit divisions, was Re: PROBLEM: XFS on ARM corruption 'Structure needs cleaning'
pavel at ucw.cz
Thu Oct 8 08:50:26 PDT 2015
On Wed 2015-08-12 08:49:45, Linus Torvalds wrote:
> On Tue, Aug 11, 2015 at 11:24 PM, Christoph Hellwig <hch at infradead.org> wrote:
> > Maybe it's time to rely on gcc to handle 64 bit divisions now?
> Ugh. gcc still does a pretty horrible job at it. While gcc knows that
> a widening 32x32->64 multiplication can be simplified, it doesn't do
> the same thing for a 64/32->64 division, and always calls __udivdi3
> for it.
> Now, __udivdi3 does avoid the general nasty case by then testing the
> upper 32 bits of the divisor against zero, so it's not entirely
> disastrous. It's just ugly.
> But perhaps more importantly, I'm not at all sure libgcc is
> kernel-safe. In particular, I'm not at all sure it *remains*
> kernel-safe. Just as an example: can you guarantee that libgcc doesn't
U-Boot relies on toolchain-provided libgcc by default, and one of reasons
we do that is so that libgcc stays sane. Yes, there's occasionally some fun
But if kernel did that, at least U-Boot would not be alone with the fun.
More information about the linux-arm-kernel