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From:   Arnd Bergmann <arnd@kernel.org>
To:     Russell King <linux@armlinux.org.uk>
Cc:     linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Arnd Bergmann <arnd@arndb.de>,
        Ard Biesheuvel <ardb@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        llvm@lists.linux.dev
Subject: [PATCH 02/14] ARM: patch: fix BE32 compilation
Date:   Tue, 28 Sep 2021 17:41:31 +0200
Message-Id: <20210928154143.2106903-3-arnd@kernel.org>
In-Reply-To: <20210928154143.2106903-1-arnd@kernel.org>
References: <20210928154143.2106903-1-arnd@kernel.org>
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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>
---
 arch/arm/include/asm/opcodes.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/opcodes.h b/arch/arm/include/asm/opcodes.h
index 6bff94b2372b..38e3eabff5c3 100644
--- a/arch/arm/include/asm/opcodes.h
+++ b/arch/arm/include/asm/opcodes.h
@@ -110,12 +110,17 @@ extern asmlinkage unsigned int arm_check_condition(u32 opcode, u32 psr);
 #define __opcode_to_mem_thumb16(x) ___opcode_identity16(x)
 #define ___asm_opcode_to_mem_arm(x) ___asm_opcode_identity32(x)
 #define ___asm_opcode_to_mem_thumb16(x) ___asm_opcode_identity16(x)
-#ifndef CONFIG_CPU_ENDIAN_BE32
+#ifdef CONFIG_CPU_ENDIAN_BE32
+#ifndef __ASSEMBLY__
 /*
  * On BE32 systems, using 32-bit accesses to store Thumb instructions will not
  * work in all cases, due to alignment constraints.  For now, a correct
- * version is not provided for BE32.
+ * version is not provided for BE32, but the prototype needs to be there
+ * to compile patch.c.
  */
+extern __u32 __opcode_to_mem_thumb32(__u32);
+#endif
+#else
 #define __opcode_to_mem_thumb32(x) ___opcode_swahw32(x)
 #define ___asm_opcode_to_mem_thumb32(x) ___asm_opcode_swahw32(x)
 #endif
-- 
2.29.2