[PATCH 02/14] ARM: patch: fix BE32 compilation

From: Arnd Bergmann
Date: Tue Sep 28 2021 - 11:42:09 EST

From: Arnd Bergmann <arnd@xxxxxxxx>

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@xxxxxxxx>
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 __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);
#define __opcode_to_mem_thumb32(x) ___opcode_swahw32(x)
#define ___asm_opcode_to_mem_thumb32(x) ___asm_opcode_swahw32(x)