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Date: Thu, 12 May 2016 12:43:46 +0100 From: Matt Fleming <matt@...eblueprint.co.uk> To: Ingo Molnar <mingo@...nel.org> Cc: Alex Thorlton <athorlton@....com>, linux-kernel@...r.kernel.org, Dimitri Sivanich <sivanich@....com>, Russ Anderson <rja@....com>, Mike Travis <travis@....com>, Borislav Petkov <bp@...e.de>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org, linux-efi@...r.kernel.org Subject: Re: [PATCH 2/2] Fix efi_call On Thu, 12 May, at 08:48:35AM, Ingo Molnar wrote: > > * Alex Thorlton <athorlton@....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.
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