Messages in this thread | | | Date | Wed, 30 Sep 2020 19:11:22 -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 07:38:15PM -0400, Arvind Sankar wrote: > On Wed, Sep 30, 2020 at 06:25:59PM -0500, Segher Boessenkool wrote: > > 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 ;-) ) > > Doesn't it just need an "r8" clobber to allow using r8d?
Yes, x86 asm is hard to read, what can I say :-) Sorry about that.
Segher
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