Avi Kivity <[email protected]> wrote:
> A "g" constraint may place a local variable in an %rsp-relative memory operand.
> but if your assembly changes %rsp, the operand points to the wrong location.
>
> An "r" constraint fixes that.
>
> Thanks to Ingo Molnar for neatly bisecting the problem.
>
> Signed-off-by: Avi Kivity <[email protected]>
>
> Index: linux-2.6/drivers/kvm/vmx.c
> ===================================================================
> --- linux-2.6.orig/drivers/kvm/vmx.c
> +++ linux-2.6/drivers/kvm/vmx.c
> @@ -1825,7 +1825,7 @@ again:
> #endif
> "setbe %0 \n\t"
> "popf \n\t"
> - : "=g" (fail)
> + : "=r" (fail)
> : "r"(vcpu->launched), "d"((unsigned long)HOST_RSP),
> "c"(vcpu),
> [rax]"i"(offsetof(struct kvm_vcpu, regs[VCPU_REGS_RAX])),
We need the following fix for 2.6.20.
[KVM] vmx: Fix register constraint in launch code
Both "=r" and "=g" breaks my build on i386:
$ make
CC [M] drivers/kvm/vmx.o
{standard input}: Assembler messages:
{standard input}:3318: Error: bad register name `%sil'
make[1]: *** [drivers/kvm/vmx.o] Error 1
make: *** [_module_drivers/kvm] Error 2
The reason is that setbe requires an 8-bit register but "=r" does not
constrain the target register to be one that has an 8-bit version on
i386.
According to
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=10153
the correct constraint is "=q".
Signed-off-by: Herbert Xu <[email protected]>
Cheers,
--
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--
diff --git a/drivers/kvm/vmx.c b/drivers/kvm/vmx.c
index ce219e3..0aa2659 100644
--- a/drivers/kvm/vmx.c
+++ b/drivers/kvm/vmx.c
@@ -1824,7 +1824,7 @@ again:
#endif
"setbe %0 \n\t"
"popf \n\t"
- : "=g" (fail)
+ : "=q" (fail)
: "r"(vcpu->launched), "d"((unsigned long)HOST_RSP),
"c"(vcpu),
[rax]"i"(offsetof(struct kvm_vcpu, regs[VCPU_REGS_RAX])),
-
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