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Date: Tue, 17 May 2016 10:46:55 +0100
From: Matt Fleming <matt@codeblueprint.co.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>, Alex Thorlton <athorlton@sgi.com>,
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        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Borislav Petkov <bp@alien8.de>, Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [GIT PULL] EFI fix
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On Tue, 17 May, at 10:04:34AM, Matt Fleming wrote:
> 
> Now I'm wondering whether other users of FRAME_BEGIN/FRAME_END make
> this same mistake. Coccinelle might be able to detect it perhaps.

A quick bit of sed turned up the code in arch/x86/entry/entry_64.S,
which looks to suffer from the same bug,

        /* rdi: arg1 ... normal C conventions. rax is saved/restored. */
        .macro THUNK name, func, put_ret_addr_in_rdi=0
        .globl \name
        .type \name, @function
\name:
        FRAME_BEGIN

        /* this one pushes 9 elems, the next one would be %rIP */
        pushq %rdi
        pushq %rsi
        pushq %rdx
        pushq %rcx
        pushq %rax
        pushq %r8
        pushq %r9
        pushq %r10
        pushq %r11

        .if \put_ret_addr_in_rdi
        /* 9*8(%rsp) is return addr on stack */
        movq 9*8(%rsp), %rdi
        .endif

With CONFIG_FRAME_POINTER=y 9*8(%rsp) is actually the value of %rbp on
entry, not the return address.