[PATCH] ARM: perf: modify kuser rmb() call to compile for Thumb-2

From: Will Deacon
Date: Wed Mar 03 2010 - 06:49:14 EST

The Thumb-2 instruction set does not provide an encoding
for sub pc, r0, #95 as present in the rmb() definition used
by perf. This results in compilation failure when using a
compiler targetting an instruction set other than ARM.

This patch redefines rmb() for ARM by casting the address
of the kuser helper to a function pointer, therefore getting
the compiler to take care of making the call.

Patch taken against tip/master.

Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Cc: Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx>
Cc: Jamie Iles <jamie.iles@xxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
tools/perf/perf.h | 4 +---
1 files changed, 1 insertions(+), 3 deletions(-)

diff --git a/tools/perf/perf.h b/tools/perf/perf.h
index 75f941b..6fb379b 100644
--- a/tools/perf/perf.h
+++ b/tools/perf/perf.h
@@ -65,9 +65,7 @@
* Use the __kuser_memory_barrier helper in the CPU helper page. See
* arch/arm/kernel/entry-armv.S in the kernel source for details.
-#define rmb() asm volatile("mov r0, #0xffff0fff; mov lr, pc;" \
- "sub pc, r0, #95" ::: "r0", "lr", "cc", \
- "memory")
+#define rmb() ((void(*)(void))0xffff0fa0)()
#define cpu_relax() asm volatile("":::"memory")


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