From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matt Fleming Subject: Re: [PATCH 2/2] Fix efi_call Date: Thu, 12 May 2016 12:43:46 +0100 Message-ID: <20160512114346.GE2728@codeblueprint.co.uk> References: <1462996545-98387-1-git-send-email-athorlton@sgi.com> <1462996545-98387-3-git-send-email-athorlton@sgi.com> <20160512064835.GB30717@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20160512064835.GB30717@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Ingo Molnar Cc: Alex Thorlton , linux-kernel@vger.kernel.org, Dimitri Sivanich , Russ Anderson , Mike Travis , Borislav Petkov , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org, linux-efi@vger.kernel.org List-Id: linux-efi@vger.kernel.org On Thu, 12 May, at 08:48:35AM, Ingo Molnar wrote: > > * Alex Thorlton 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.