linux-kernel - Re: [PATCH] arm64: drop linker script hack to hide __efistub

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Message-ID: <CAKwvOdnZKatfVa=dDSBbkrhfJPhsaD_FxVt4YYAvHMQOUimPeg@mail.gmail.com>
Date:   Fri, 30 Nov 2018 16:20:42 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH] arm64: drop linker script hack to hide __efistub_ symbols

On Fri, Nov 30, 2018 at 3:36 AM Ard Biesheuvel
<ard.biesheuvel@...aro.org> wrote:
>
> Commit 1212f7a16af4 ("scripts/kallsyms: filter arm64's __efistub_
> symbols") updated the kallsyms code to filter out symbols with
> the __efistub_ prefix explicitly, so we no longer require the
> hack in our linker script to emit them as absolute symbols.
>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>

Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>

Tested linking with bfd and booting in qemu.  Thanks Ard!  lld still
has some further bugs for us to work out, but this should help
simplify things for us.

> ---
>  arch/arm64/kernel/image.h | 46 +++++++++++++++------------------------
>  1 file changed, 18 insertions(+), 28 deletions(-)
>
> diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h
> index a820ed07fb80..8da289dc843a 100644
> --- a/arch/arm64/kernel/image.h
> +++ b/arch/arm64/kernel/image.h
> @@ -75,16 +75,6 @@
>
>  __efistub_stext_offset = stext - _text;
>
> -/*
> - * Prevent the symbol aliases below from being emitted into the kallsyms
> - * table, by forcing them to be absolute symbols (which are conveniently
> - * ignored by scripts/kallsyms) rather than section relative symbols.
> - * The distinction is only relevant for partial linking, and only for symbols
> - * that are defined within a section declaration (which is not the case for
> - * the definitions below) so the resulting values will be identical.
> - */
> -#define KALLSYMS_HIDE(sym)     ABSOLUTE(sym)
> -
>  /*
>   * The EFI stub has its own symbol namespace prefixed by __efistub_, to
>   * isolate it from the kernel proper. The following symbols are legally
> @@ -94,28 +84,28 @@ __efistub_stext_offset = stext - _text;
>   * linked at. The routines below are all implemented in assembler in a
>   * position independent manner
>   */
> -__efistub_memcmp               = KALLSYMS_HIDE(__pi_memcmp);
> -__efistub_memchr               = KALLSYMS_HIDE(__pi_memchr);
> -__efistub_memcpy               = KALLSYMS_HIDE(__pi_memcpy);
> -__efistub_memmove              = KALLSYMS_HIDE(__pi_memmove);
> -__efistub_memset               = KALLSYMS_HIDE(__pi_memset);
> -__efistub_strlen               = KALLSYMS_HIDE(__pi_strlen);
> -__efistub_strnlen              = KALLSYMS_HIDE(__pi_strnlen);
> -__efistub_strcmp               = KALLSYMS_HIDE(__pi_strcmp);
> -__efistub_strncmp              = KALLSYMS_HIDE(__pi_strncmp);
> -__efistub_strrchr              = KALLSYMS_HIDE(__pi_strrchr);
> -__efistub___flush_dcache_area  = KALLSYMS_HIDE(__pi___flush_dcache_area);
> +__efistub_memcmp               = __pi_memcmp;
> +__efistub_memchr               = __pi_memchr;
> +__efistub_memcpy               = __pi_memcpy;
> +__efistub_memmove              = __pi_memmove;
> +__efistub_memset               = __pi_memset;
> +__efistub_strlen               = __pi_strlen;
> +__efistub_strnlen              = __pi_strnlen;
> +__efistub_strcmp               = __pi_strcmp;
> +__efistub_strncmp              = __pi_strncmp;
> +__efistub_strrchr              = __pi_strrchr;
> +__efistub___flush_dcache_area  = __pi___flush_dcache_area;
>
>  #ifdef CONFIG_KASAN
> -__efistub___memcpy             = KALLSYMS_HIDE(__pi_memcpy);
> -__efistub___memmove            = KALLSYMS_HIDE(__pi_memmove);
> -__efistub___memset             = KALLSYMS_HIDE(__pi_memset);
> +__efistub___memcpy             = __pi_memcpy;
> +__efistub___memmove            = __pi_memmove;
> +__efistub___memset             = __pi_memset;
>  #endif
>
> -__efistub__text                        = KALLSYMS_HIDE(_text);
> -__efistub__end                 = KALLSYMS_HIDE(_end);
> -__efistub__edata               = KALLSYMS_HIDE(_edata);
> -__efistub_screen_info          = KALLSYMS_HIDE(screen_info);
> +__efistub__text                        = _text;
> +__efistub__end                 = _end;
> +__efistub__edata               = _edata;
> +__efistub_screen_info          = screen_info;
>
>  #endif
>
> --
> 2.19.1
>


-- 
Thanks,
~Nick Desaulniers