linux-kernel - Re: [PATCH -next 1/3] arm64: efi-header: Mark efi header as data

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Message-ID: <CAMj1kXGSjGr_yBC_9DiFu4k3JpDRPB+BPuKdNu2XeSWT2BSZvQ@mail.gmail.com>
Date:   Thu, 22 Sep 2022 15:13:59 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Chen Zhongjin <chenzhongjin@...wei.com>
Cc:     linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, herbert@...dor.apana.org.au,
        davem@...emloft.net, catalin.marinas@....com, will@...nel.org,
        broonie@...nel.org, maz@...nel.org, mark.rutland@....com,
        anshuman.khandual@....com
Subject: Re: [PATCH -next 1/3] arm64: efi-header: Mark efi header as data

On Thu, 22 Sept 2022 at 15:08, Chen Zhongjin <chenzhongjin@...wei.com> wrote:
>
> This file only contains a set of constants forming the efi header.
>
> Make the constants part of data symbols by wrapping them with
> SYM_DATA.
>
> Signed-off-by: Julien Thierry <jthierry@...hat.com>
> Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>
> Reviewed-by: Mark Brown <broonie@...nel.org>

Why is this necessary? These are not emitted into a .text section, and
are not even covered by the kernel's mapping of memory. So the .L
prefixed labels are deliberate: it prevents the symbols from polluting
the symbol namespace with symbols pointing nowhere.


> ---
>  arch/arm64/kernel/efi-header.S | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/arm64/kernel/efi-header.S b/arch/arm64/kernel/efi-header.S
> index 28d8a5dca5f1..3eacd27ab761 100644
> --- a/arch/arm64/kernel/efi-header.S
> +++ b/arch/arm64/kernel/efi-header.S
> @@ -28,6 +28,7 @@
>         .macro  __EFI_PE_HEADER
>  #ifdef CONFIG_EFI
>         .set    .Lpe_header_offset, . - .L_head
> +SYM_DATA_START_LOCAL(arm64_efi_header)
>         .long   PE_MAGIC
>         .short  IMAGE_FILE_MACHINE_ARM64                // Machine
>         .short  .Lsection_count                         // NumberOfSections
> @@ -160,6 +161,7 @@
>
>         .balign SEGMENT_ALIGN
>  .Lefi_header_end:
> +SYM_DATA_END_LABEL(arm64_efi_header, SYM_L_LOCAL, efi_header_end)
>  #else
>         .set    .Lpe_header_offset, 0x0
>  #endif
> --
> 2.17.1
>