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

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Date:   Thu, 3 Dec 2020 19:00:30 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Fangrui Song <maskray@...gle.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        linux-arch <linux-arch@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] firmware_loader: Align .builtin_fw to 8

On Thu, Dec 3, 2020 at 6:05 PM 'Fangrui Song' via Clang Built Linux
<clang-built-linux@...glegroups.com> 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.
>
> 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>

I found the same thing in randconfig testing, but you beat me to
sending the fix.