On 3/26/19 4:25 AM, Maxim Kuvyrkov wrote:
On Mar 26, 2019, at 12:22 AM, Vladimir Makarov <vmaka...@redhat.com> wrote:
Jeff Law recently found that my latest patch break some existing code
compilation (the code is big to make test out of it).
Here is the patch to fix it. The patch was successfully bootstrapped on
x86-64. The patch actually results in less new transformations the previous
patch introduced. So it should be safe.
Committed as rev. 269924.
Hi Vladimir,
FWIW, this fixed linux kernel builds on AArch64 and ARM, which your first patch
caused.
The failure was:
===
slub.s: Assembler messages:
slub.s:26: Error: reg pair must start from even reg at operand 1 -- `casp
x1,x0,x3,x5,[x6]'
===
from a reduced testcase:
===
void *a;
long b, c;
void d(void) {
typeof(0) e=0;
asm(" casp\t%[old1], %[old2], %[new1], %[new2], %[v]\n"
: [old1] "+&r"(b), [old2] "+&r"(c), [v] "+Q"(a)
: [new1] "r"(d), [new2] "r"(e));
}
===
Is this the same bug that Jeff reported?
Yes, it looks similar (reg pair and casp). I did know it was a kernel. I only
had a preprocessed file slub.i.
The reduced case is actually wrong. The constraints +&r does not guarantee
that b and c will be in the subsequent regs. In the original test case b and c
were also local *register* variables (x0 and x1). Generally speaking even this
does no guarantee (according to the documentation) that the original variable
values will be in subsequent regs for casp. But as people assume such
(undocumented) semantics, we should maintain this.
