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

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

[Will Deacon]

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@arm.com>
Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Jamie Iles <jamie.iles@picochip.com>
Cc: Ingo Molnar <mingo@elte.hu>
---
 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")
 #endif
 
-- 
1.6.3.3

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

[Jamie Iles]

On Wed, Mar 03, 2010 at 11:47:58AM +0000, Will Deacon wrote:
> 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@arm.com>
> Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>
> Cc: Jamie Iles <jamie.iles@picochip.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> ---
>  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)()
This will take care of doing the CPU barrier but don't we still need a
compiler memory barrier? I guess you could do:

#define rmb() ({ \
		((void(*)(void))0xffff0fa0)(); \
		asm volatile("" ::: "memory"); \
	})

Jamie

[tip:perf/pebs] perf, ARM: Modify kuser rmb() call to compile for Thumb-2

[tip-bot for Will Deacon]

Commit-ID:  da7196e1f986c846ffa8b2ec385223fad38e8518
Gitweb:     http://git.kernel.org/tip/da7196e1f986c846ffa8b2ec385223fad38e8518
Author:     Will Deacon <will.deacon@arm.com>
AuthorDate: Wed, 3 Mar 2010 11:47:58 +0000
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Thu, 4 Mar 2010 12:13:28 +0100

perf, ARM: Modify kuser rmb() call to compile for Thumb-2

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@arm.com>
Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Jamie Iles <jamie.iles@picochip.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1267616878-2154-1-git-send-email-will.deacon@arm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 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")
 #endif