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SubjectRe: linux-next: build failure after merge of the vfs tree
On Fri, Sep 25, 2020 at 10:01:28PM +1000, Stephen Rothwell wrote:
> $ x86_64-linux-gnu-gcc --version
> x86_64-linux-gnu-gcc (Debian 10.2.0-9) 10.2.0
> $ x86_64-linux-gnu-ld --version
> GNU ld (GNU Binutils for Debian) 2.35
>
> and the gcc plugins don't get built for the allnoconfig builds.

> I reverted my Revert commit after I finished linux-next today and built
> the x86_64 allnoconfig verion of lib/iov_iter.s:
>
> $ grep -A 1 '41 "/home/sfr/next/next/arch/x86/include/asm/barrier.h"' lib/iov_iter.s
> # 41 "/home/sfr/next/next/arch/x86/include/asm/barrier.h" 1
> cmp $140737488351232,%rdx; sbb %rcx,%rcx; #, uaddr, mask

Wait a sec...
static inline unsigned long array_index_mask_nospec(unsigned long index,
unsigned long size)
{
unsigned long mask;

asm volatile ("cmp %1,%2; sbb %0,%0;"
:"=r" (mask)
:"g"(size),"r" (index)
:"cc");
return mask;
}

used with large constant size will blow up - "g" is wrong, since cmp allows
64bit arguments to be register or memory ones; immediates can't go past
32bit.

Looks like on the configs where it builds we end up with not seeing it's
a constant...

Josh, any ideas? We could, of course, make it "r"(size), but that would
be unpleasant in all existing callers...

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