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From:   Linus Walleij <linus.walleij@linaro.org>
Date:   Tue, 28 Sep 2021 23:33:28 +0200
Message-ID: <CACRpkdY2cjyzCtAwzuOE-4XoGNcxEzP+xEUWmUUs-b9wW+pjsA@mail.gmail.com>
Subject: Re: [PATCH 02/14] ARM: patch: fix BE32 compilation
To:     Arnd Bergmann <arnd@kernel.org>
Cc:     Russell King <linux@armlinux.org.uk>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Ard Biesheuvel <ardb@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        llvm@lists.linux.dev
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On Tue, Sep 28, 2021 at 5:42 PM Arnd Bergmann <arnd@kernel.org> wrote:

> From: Arnd Bergmann <arnd@arndb.de>
>
> On BE32 kernels, the __opcode_to_mem_thumb32() interface is intentionally
> not defined, but it is referenced whenever runtime patching is enabled
> for the kernel, which may be for ftrace, jump label, kprobes or kgdb:
>
> arch/arm/kernel/patch.c: In function '__patch_text_real':
> arch/arm/kernel/patch.c:94:32: error: implicit declaration of function '__opcode_to_mem_thumb32' [-Werror=implicit-function-declaration]
>    94 |                         insn = __opcode_to_mem_thumb32(insn);
>       |                                ^~~~~~~~~~~~~~~~~~~~~~~
>
> Since BE32 kernels never run Thumb2 code, we never end up using the
> result of this call, so providing an extern declaration without
> a definition makes it build correctly.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Looks good to me!
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

Yours,
Linus Walleij