linux-kernel - [PATCH] arm/ftrace: fix building on BE32

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Date:   Wed,  8 Jan 2020 15:36:30 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Russell King <linux@...linux.org.uk>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        ard.biesheuvel@...aro.org, james.morse@....com, rabin@....in,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Enrico Weigelt <info@...ux.net>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] arm/ftrace: fix building on BE32

Compiling patch.c on BE32 fails because there is no definition
of __opcode_to_mem_thumb32()

arch/arm/kernel/patch.c: In function '__patch_text_real':
arch/arm/kernel/patch.c:94:11: error: implicit declaration of function '__opcode_to_mem_thumb32' [-Werror=implicit-function-declaration]

Since we don't actually call it, only a declaration is required
here, add one without a definition that fixes the build here
but will cause a link failure if someone actually relies on the
result.

Fixes: 5a735583b764 ("arm/ftrace: Use __patch_text()")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
Not sure if this version is any less ugly than the first
approach of adding an #ifdef in patch.c
---
 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..f75f59c1257a 100644
--- a/arch/arm/include/asm/opcodes.h
+++ b/arch/arm/include/asm/opcodes.h
@@ -110,14 +110,19 @@ 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
 /*
  * 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, only an extern declaration to allow
+ * compiling patch.c
  */
+#ifndef CONFIG_CPU_ENDIAN_BE32
 #define __opcode_to_mem_thumb32(x) ___opcode_swahw32(x)
 #define ___asm_opcode_to_mem_thumb32(x) ___asm_opcode_swahw32(x)
+#else
+#ifndef __ASSEMBLY__
+extern unsigned __opcode_to_mem_thumb32(unsigned);
+#endif
 #endif
 
 #endif /* ! CONFIG_CPU_ENDIAN_BE8 */
-- 
2.20.0