linux-kernel - Re: [PATCH] x86/unwind/orc: Fix ORC unwind table alignment

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Message-ID: <CAKwvOdmHe-bkt34E5yf81GoiFRHR8EPnu8wqk2aD2u8P_4Q5jQ@mail.gmail.com>
Date:   Wed, 6 Mar 2019 10:44:01 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Dmitry Golovin <dima@...ovin.in>,
        Sedat Dilek <sedat.dilek@...il.com>
Subject: Re: [PATCH] x86/unwind/orc: Fix ORC unwind table alignment

On Wed, Mar 6, 2019 at 9:08 AM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> The .orc_unwind section is a packed array of 6-byte structs.  It's
> currently aligned to 6 bytes, which is causing warnings in the LLD
> linker.
>
> Six isn't a power of two, so it's not a valid alignment value.  The
> actual alignment doesn't matter much because it's an array of packed
> structs.  An alignment of two is sufficient.  In reality it always gets
> aligned to four bytes because it comes immediately after the
> 4-byte-aligned .orc_unwind_ip section.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/218
> Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder")

Thanks for the patch Josh, we appreciate it.  It looks like
ee9f8fce9964 landed in v4.14-rc1.  Should we CC stable?

> Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Reported-by: Dmitry Golovin <dima@...ovin.in>
> Reported-by: Sedat Dilek <sedat.dilek@...il.com>
> Tested-by: Sedat Dilek <sedat.dilek@...il.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> ---
>  include/asm-generic/vmlinux.lds.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 3d7a6a9c2370..f8f6f04c4453 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -733,7 +733,7 @@
>                 KEEP(*(.orc_unwind_ip))                                 \
>                 __stop_orc_unwind_ip = .;                               \
>         }                                                               \
> -       . = ALIGN(6);                                                   \
> +       . = ALIGN(2);                                                   \
>         .orc_unwind : AT(ADDR(.orc_unwind) - LOAD_OFFSET) {             \
>                 __start_orc_unwind = .;                                 \
>                 KEEP(*(.orc_unwind))                                    \
> --
> 2.17.2
>


-- 
Thanks,
~Nick Desaulniers