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

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Message-ID: <CA+icZUUXZmDLOXbcj6vZi6+ZTC41VbH77CViHFRmQfxiMBqYtw@mail.gmail.com>
Date:   Tue, 14 Jul 2020 11:34:12 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Jian Cai <caij2003@...il.com>
Cc:     jiancai@...gle.com, Nick Desaulniers <ndesaulniers@...gle.com>,
        manojgupta@...gle.com, Brian Gerst <brgerst@...il.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        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@...r.kernel.org,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] x86/entry: add compatibility with IAS

On Tue, Jul 14, 2020 at 12:40 AM 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>
> Suggested-by: Brian Gerst <brgerst@...il.com>
> Suggested-by: Arvind Sankar <nivedita@...m.mit.edu>
> Tested-by: Sedat Dilek <sedat.dilek@...il.com>
> Signed-off-by: Jian Cai <caij2003@...il.com>

Hi Jian,

thanks for the update!

I am glad to see that some Linux/x86 assembler "monsters" jumped on the train.

So, your patch with reviewer's comment got several iterations?
Not sure if you are aware of the process of submitting patches (see [1])?

It is common to add a ChangeLog below commit-message-body and diffstat
means add below "--".
Something like:
--
Changes v1 -> v2:
- I did some cool stuff to improve this

While at it... Please add your version-of-patch to the subject-line:
You can do this via "git format-patch --signoff --subject-prefix="PATCH v2".
There might be other cool git tricks I do not know.

Hope I was no "Uberlehrer".

- Sedat -

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst

> ---
>  arch/x86/include/asm/idtentry.h | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
> index f3d70830bf2a..5efaaed34eda 100644
> --- a/arch/x86/include/asm/idtentry.h
> +++ b/arch/x86/include/asm/idtentry.h
> @@ -469,16 +469,15 @@ __visible noinstr void func(struct pt_regs *regs,                 \
>         .align 8
>  SYM_CODE_START(irq_entries_start)
>      vector=FIRST_EXTERNAL_VECTOR
> -    pos = .
>      .rept (FIRST_SYSTEM_VECTOR - FIRST_EXTERNAL_VECTOR)
>         UNWIND_HINT_IRET_REGS
> +0 :
>         .byte   0x6a, vector
>         jmp     asm_common_interrupt
>         nop
>         /* Ensure that the above is 8 bytes max */
> -       . = pos + 8
> -    pos=pos+8
> -    vector=vector+1
> +       . = 0b + 8
> +       vector = vector+1
>      .endr
>  SYM_CODE_END(irq_entries_start)
>
> @@ -486,16 +485,15 @@ SYM_CODE_END(irq_entries_start)
>         .align 8
>  SYM_CODE_START(spurious_entries_start)
>      vector=FIRST_SYSTEM_VECTOR
> -    pos = .
>      .rept (NR_VECTORS - FIRST_SYSTEM_VECTOR)
>         UNWIND_HINT_IRET_REGS
> +0 :
>         .byte   0x6a, vector
>         jmp     asm_spurious_interrupt
>         nop
>         /* Ensure that the above is 8 bytes max */
> -       . = pos + 8
> -    pos=pos+8
> -    vector=vector+1
> +       . = 0b + 8
> +       vector = vector+1
>      .endr
>  SYM_CODE_END(spurious_entries_start)
>  #endif
> --
> 2.27.0.383.g050319c2ae-goog
>