linux-kernel - Re: [PATCH 1/5] efi/arm: Remove __efistub

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Date:   Thu, 16 Apr 2020 09:50:36 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     linux-efi <linux-efi@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        X86 ML <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/5] efi/arm: Remove __efistub_global annotation

On Thu, 16 Apr 2020 at 00:15, Arvind Sankar <nivedita@...m.mit.edu> wrote:
>
> Instead of using __efistub_global to force variables into the .data
> section, leave them in the .bss but pull the EFI stub's .bss section
> into .data in the linker script for the compressed kernel.
>
> Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>

Reviewed-by: Ard Biesheuvel <ardb@...nel.org>

> ---
>  arch/arm/boot/compressed/vmlinux.lds.S | 2 +-
>  drivers/firmware/efi/libstub/Makefile  | 7 ++++---
>  drivers/firmware/efi/libstub/efistub.h | 2 +-
>  3 files changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm/boot/compressed/vmlinux.lds.S b/arch/arm/boot/compressed/vmlinux.lds.S
> index b247f399de71..b6793c7932a9 100644
> --- a/arch/arm/boot/compressed/vmlinux.lds.S
> +++ b/arch/arm/boot/compressed/vmlinux.lds.S
> @@ -78,7 +78,7 @@ SECTIONS
>       * The EFI stub always executes from RAM, and runs strictly before the
>       * decompressor, so we can make an exception for its r/w data, and keep it
>       */
> -    *(.data.efistub)
> +    *(.data.efistub .bss.efistub)
>      __pecoff_data_end = .;
>
>      /*
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index 094eabdecfe6..45ffe0822df1 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -100,8 +100,9 @@ quiet_cmd_stubcopy = STUBCPY $@
>
>  #
>  # ARM discards the .data section because it disallows r/w data in the
> -# decompressor. So move our .data to .data.efistub, which is preserved
> -# explicitly by the decompressor linker script.
> +# decompressor. So move our .data to .data.efistub and .bss to .bss.efistub,
> +# which are preserved explicitly by the decompressor linker script.
>  #
> -STUBCOPY_FLAGS-$(CONFIG_ARM)   += --rename-section .data=.data.efistub
> +STUBCOPY_FLAGS-$(CONFIG_ARM)   += --rename-section .data=.data.efistub \
> +                                  --rename-section .bss=.bss.efistub,load,alloc
>  STUBCOPY_RELOC-$(CONFIG_ARM)   := R_ARM_ABS
> diff --git a/drivers/firmware/efi/libstub/efistub.h b/drivers/firmware/efi/libstub/efistub.h
> index bd0b86b63936..a92d42ffd9f7 100644
> --- a/drivers/firmware/efi/libstub/efistub.h
> +++ b/drivers/firmware/efi/libstub/efistub.h
> @@ -25,7 +25,7 @@
>  #define EFI_ALLOC_ALIGN                EFI_PAGE_SIZE
>  #endif
>
> -#if defined(CONFIG_ARM) || defined(CONFIG_X86)
> +#if defined(CONFIG_X86)
>  #define __efistub_global       __section(.data)
>  #else
>  #define __efistub_global
> --
> 2.24.1
>