linux-kernel - Re: [PATCH] x86/entry: add compatibility with IAS

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Message-ID: <CAMzpN2idjMEFXvxZKOwDggO1MAFESRE4E_Ch55gfPeLFipxDqw@mail.gmail.com>
Date:   Sun, 12 Jul 2020 22:33:20 -0400
From:   Brian Gerst <brgerst@...il.com>
To:     Jian Cai <caij2003@...il.com>
Cc:     jiancai@...gle.com, Nick Desaulniers <ndesaulniers@...gle.com>,
        manojgupta@...gle.com, Sedat Dilek <sedat.dilek@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] x86/entry: add compatibility with IAS

On Sun, Jul 12, 2020 at 9:26 PM Jian Cai <caij2003@...il.com> wrote:
>
> Clang's integrated assembler does not allow symbols with non-absolute
> values to be reassigned. This patch allows the affected code to be
> compatible with IAS.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1043
> Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Reported-by: Sedat Dilek <sedat.dilek@...il.com>
> Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Tested-by: Sedat Dilek <sedat.dilek@...il.com>
> Signed-off-by: Jian Cai <caij2003@...il.com>
> ---
>  arch/x86/include/asm/idtentry.h | 22 ++++++++++------------
>  1 file changed, 10 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
> index f3d70830bf2a..77beed2cd6d9 100644
> --- a/arch/x86/include/asm/idtentry.h
> +++ b/arch/x86/include/asm/idtentry.h
> @@ -468,34 +468,32 @@ __visible noinstr void func(struct pt_regs *regs,                 \
>   */
>         .align 8
>  SYM_CODE_START(irq_entries_start)
> -    vector=FIRST_EXTERNAL_VECTOR
> -    pos = .
> +    i = 1

Start with index 0.

> +    pos1 = .

pos1 is unnecessary, as it's equal to irq_entries_start.

>      .rept (FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR)
>         UNWIND_HINT_IRET_REGS
> -       .byte   0x6a, vector
> +       .byte   0x6a, FIRST_EXTERNAL_VECTOR + i - 1
>         jmp     asm_common_interrupt
>         nop
>         /* Ensure that the above is 8 bytes max */
> -       . = pos + 8
> -    pos=pos+8
> -    vector=vector+1
> +       . = pos1 + 8 * i
> +       i = i + 1

If you swap these two lines then the index will be correct for the
next stub if you start at 0..

>      .endr
>  SYM_CODE_END(irq_entries_start)
>
>  #ifdef CONFIG_X86_LOCAL_APIC
>         .align 8
>  SYM_CODE_START(spurious_entries_start)
> -    vector=FIRST_SYSTEM_VECTOR
> -    pos = .
> +    i = 1
> +    pos2 = .
>      .rept (NR_VECTORS - FIRST_SYSTEM_VECTOR)
>         UNWIND_HINT_IRET_REGS
> -       .byte   0x6a, vector
> +       .byte   0x6a, FIRST_SYSTEM_VECTOR + i - 1
>         jmp     asm_spurious_interrupt
>         nop
>         /* Ensure that the above is 8 bytes max */
> -       . = pos + 8
> -    pos=pos+8
> -    vector=vector+1
> +       . = pos2 + 8 * i
> +       i = i + 1
>      .endr
>  SYM_CODE_END(spurious_entries_start)
>  #endif

--
Brian Gerst