Re: [PATCH 2/2] Fix efi_call

Matt Fleming
2016-05-12T11:43:46Z

On Thu, 12 May, at 08:48:35AM, Ingo Molnar wrote:
>
> * Alex Thorlton <athorlton@sgi.com> wrote:
>
> > The efi_call assembly code has a slight error that prevents us from
> > using arguments 7 and higher, which will be passed in on the stack.
> >
> > mov (%rsp), %rax
> > mov 8(%rax), %rax
> > ...
> > mov %rax, 40(%rsp)
> >
> > This code goes and grabs the return address for the current stack frame,
> > and puts it on the stack, next the 5th argument for the EFI runtime
> > call. Considering the fact that having the return address in that
> > position on the stack makes no sense, I'm guessing that the intent of
> > this code was actually to grab an argument off the stack frame for this
> > call and place it into the frame for the next one.
> >
> > The small change to that offset (i.e. 8(%rax) to 16(%rax)) ensures that
> > we grab the 7th argument off the stack, and pass it as the 6th argument
> > to the EFI runtime function that we're about to call. This change gets
> > our EFI runtime calls that need to pass more than 6 arguments working
> > again.
>
> I suppose the SGI/UV code is the only one using 7 arguments or more? Might make
> sense to point that out in the changelog.

Yeah, I included that info when I applied this patch.