linux-kernel - Re: [PATCH v2] firmware_loader: Align .builtin

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Message-ID: <20210205190834.GC461042@localhost>
Date:   Fri, 5 Feb 2021 12:08:34 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        kernel test robot <lkp@...el.com>,
        Fangrui Song <maskray@...gle.com>
Subject: Re: [PATCH v2] firmware_loader: Align .builtin_fw to 8

On Mon, Dec 07, 2020 at 09:46:46PM -0800, Fangrui Song wrote:
> arm64 references the start address of .builtin_fw (__start_builtin_fw)
> with a pair of R_AARCH64_ADR_PREL_PG_HI21/R_AARCH64_LDST64_ABS_LO12_NC
> relocations. The compiler is allowed to emit the
> R_AARCH64_LDST64_ABS_LO12_NC relocation because struct builtin_fw in
> include/linux/firmware.h is 8-byte aligned.
> 
> The R_AARCH64_LDST64_ABS_LO12_NC relocation requires the address to be a
> multiple of 8, which may not be the case if .builtin_fw is empty.
> Unconditionally align .builtin_fw to fix the linker error. 32-bit
> architectures could use ALIGN(4) but that would add unnecessary
> complexity, so just use ALIGN(8).
> 
> Fixes: 5658c76 ("firmware: allow firmware files to be built into kernel image")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1204
> Reported-by: kernel test robot <lkp@...el.com>
> Signed-off-by: Fangrui Song <maskray@...gle.com>
> Acked-by: Arnd Bergmann <arnd@...db.de>

Acked-by: Nathan Chancellor <nathan@...nel.org>

Andrew, is there any way to get this picked up with the following tags
for 5.11?

Tested-by: Douglas Anderson <dianders@...omium.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>

If not, please let me know and I can try to shuffle this along to Linus
next week.

> 
> ---
> Change in v2:
> * Use output section alignment instead of inappropriate ALIGN_FUNCTION()
> ---
>  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 b2b3d81b1535..b97c628ad91f 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -459,7 +459,7 @@
>  	}								\
>  									\
>  	/* Built-in firmware blobs */					\
> -	.builtin_fw        : AT(ADDR(.builtin_fw) - LOAD_OFFSET) {	\
> +	.builtin_fw : AT(ADDR(.builtin_fw) - LOAD_OFFSET) ALIGN(8) {	\
>  		__start_builtin_fw = .;					\
>  		KEEP(*(.builtin_fw))					\
>  		__end_builtin_fw = .;					\
> -- 
> 2.29.2.576.ga3fc446d84-goog
>