Messages in this thread | | | Date | Wed, 30 Sep 2020 18:25:59 -0500 | From | Segher Boessenkool <> | Subject | Re: [PATCH v4 04/17] x86/acrn: Introduce hypercall interfaces |
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On Wed, Sep 30, 2020 at 12:14:03PM -0700, Nick Desaulniers wrote: > Do we need register local storage here?
Depends what you want. It looks like you do:
> static inline long bar(unsigned long hcall_id) > { > long result; > asm volatile("movl %1, %%r8d\n\t" > "vmcall\n\t" > : "=a" (result) > : "ir" (hcall_id) > : ); > return result; > }
"result" as output from the asm is in %rax, and the compiler will shuffle that to wherever it needs it as the function return value. That part will work fine.
But how you are accessing %r8d is not correct, that needs to be a local register asm (or r8 be made a fixed reg, probably not what you want ;-) )
Segher
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