* [PATCH] x86emul: replace further UB shifts
@ 2020-08-04 10:13 Jan Beulich
2020-08-04 13:19 ` Andrew Cooper
0 siblings, 1 reply; 2+ messages in thread
From: Jan Beulich @ 2020-08-04 10:13 UTC (permalink / raw)
To: xen-devel; +Cc: Andrew Cooper, Wei Liu, Roger Pau Monné
I have no explanation how I managed to overlook these while putting
together what is now b6a907f8c83d ("x86emul: replace UB shifts").
Signed-off-by: Jan Beulich <jbeulich@suse.com>
--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -9735,7 +9735,7 @@ x86_emulate(
rc = ops->read(ea.mem.seg,
truncate_ea(ea.mem.off +
- (idx << state->sib_scale)),
+ idx * (1 << state->sib_scale)),
(void *)mmvalp + i * op_bytes, op_bytes, ctxt);
if ( rc != X86EMUL_OKAY )
{
@@ -9857,7 +9857,8 @@ x86_emulate(
continue;
rc = ops->read(ea.mem.seg,
- truncate_ea(ea.mem.off + (idx << state->sib_scale)),
+ truncate_ea(ea.mem.off +
+ idx * (1 << state->sib_scale)),
(void *)mmvalp + i * op_bytes, op_bytes, ctxt);
if ( rc != X86EMUL_OKAY )
{
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: [PATCH] x86emul: replace further UB shifts
2020-08-04 10:13 [PATCH] x86emul: replace further UB shifts Jan Beulich
@ 2020-08-04 13:19 ` Andrew Cooper
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Cooper @ 2020-08-04 13:19 UTC (permalink / raw)
To: Jan Beulich, xen-devel; +Cc: Wei Liu, Roger Pau Monné
On 04/08/2020 11:13, Jan Beulich wrote:
> I have no explanation how I managed to overlook these while putting
> together what is now b6a907f8c83d ("x86emul: replace UB shifts").
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
I've just checked, and GCC 9.3.0 does convert this pattern back to a
single shift instruction, so at least we're not left with real mul
instructions.
~Andrew
^ permalink raw reply [flat|nested] 2+ messages in thread
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