linux-kernel - [PATCH 3/3] ARM: kprobes: use "I" constraint for inline assembly offsets

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Message-Id: <1454941613-2775081-3-git-send-email-arnd@arndb.de>
Date:	Mon,  8 Feb 2016 15:25:58 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Russell King <linux@....linux.org.uk>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] ARM: kprobes: use "I" constraint for inline assembly offsets

build-testing with clang showed that the "J" constraint does not take
positive arguments on clang when building in for Thumb-2:

core.c:540:3: error: invalid operand for inline asm constraint 'J'

This has been reported as llvm bug https://llvm.org/bugs/show_bug.cgi?id=26061

However, looking at the source code in depth, I found that the
kernel is also wrong, and it should not use "J" at all, but should
use "I" to pass an immediate argument to the inline assembly when that
is used as an offset to an 'ldr' instruction rather than the 'sub'
argument.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 arch/arm/probes/kprobes/core.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm/probes/kprobes/core.c b/arch/arm/probes/kprobes/core.c
index a4ec240ee7ba..4b34b40ca917 100644
--- a/arch/arm/probes/kprobes/core.c
+++ b/arch/arm/probes/kprobes/core.c
@@ -570,10 +570,10 @@ void __kprobes jprobe_return(void)
 		:
 		: "r" (kcb->jprobe_saved_regs.ARM_sp),
 		  "I" (sizeof(struct pt_regs) * 2),
-		  "J" (offsetof(struct pt_regs, ARM_sp)),
-		  "J" (offsetof(struct pt_regs, ARM_pc)),
-		  "J" (offsetof(struct pt_regs, ARM_cpsr)),
-		  "J" (offsetof(struct pt_regs, ARM_lr))
+		  "I" (offsetof(struct pt_regs, ARM_sp)),
+		  "I" (offsetof(struct pt_regs, ARM_pc)),
+		  "I" (offsetof(struct pt_regs, ARM_cpsr)),
+		  "I" (offsetof(struct pt_regs, ARM_lr))
 		: "memory", "cc");
 }
 
-- 
2.7.0