[PATCH] powerpc/perf_events: Implement perf_arch_fetch_caller_regs for powerpc

[Paul Mackerras <paulus@samba.org>]

This implements a powerpc version of perf_arch_fetch_caller_regs.
It's implemented in assembly because that way we can be sure there
isn't a stack frame for perf_arch_fetch_caller_regs.  If it was in
C, gcc might or might not create a stack frame for it, which would
affect the number of levels we have to skip.  It's not ifdef'd
because it is only 14 instructions long.

With this, we see results from perf record -e lock:lock_acquire like
this:

# Samples: 24878
#
# Overhead         Command      Shared Object  Symbol
# ........  ..............  .................  ......
#
    14.99%            perf  [kernel.kallsyms]  [k] ._raw_spin_lock
                      |
                      --- ._raw_spin_lock
                         |          
                         |--25.00%-- .alloc_fd
                         |          (nil)
                         |          |          
                         |          |--50.00%-- .anon_inode_getfd
                         |          |          .sys_perf_event_open
                         |          |          syscall_exit
                         |          |          syscall
                         |          |          create_counter
                         |          |          __cmd_record
                         |          |          run_builtin
                         |          |          main
                         |          |          0xfd2e704
                         |          |          0xfd2e8c0
                         |          |          (nil)

... etc.

Signed-off-by: Paul Mackerras <paulus@samba.org>
---
 arch/powerpc/include/asm/asm-compat.h |    2 ++
 arch/powerpc/kernel/misc.S            |   20 ++++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/arch/powerpc/include/asm/asm-compat.h b/arch/powerpc/include/asm/asm-compat.h
index c1b475a..a9b91ed 100644
--- a/arch/powerpc/include/asm/asm-compat.h
+++ b/arch/powerpc/include/asm/asm-compat.h
@@ -28,6 +28,7 @@
 #define PPC_LLARX(t, a, b, eh)	PPC_LDARX(t, a, b, eh)
 #define PPC_STLCX	stringify_in_c(stdcx.)
 #define PPC_CNTLZL	stringify_in_c(cntlzd)
+#define PPC_LR_STKOFF	16
 
 /* Move to CR, single-entry optimized version. Only available
  * on POWER4 and later.
@@ -51,6 +52,7 @@
 #define PPC_STLCX	stringify_in_c(stwcx.)
 #define PPC_CNTLZL	stringify_in_c(cntlzw)
 #define PPC_MTOCRF	stringify_in_c(mtcrf)
+#define PPC_LR_STKOFF	4
 
 #endif
 
diff --git a/arch/powerpc/kernel/misc.S b/arch/powerpc/kernel/misc.S
index 2d29752..4459500 100644
--- a/arch/powerpc/kernel/misc.S
+++ b/arch/powerpc/kernel/misc.S
@@ -127,3 +127,23 @@ _GLOBAL(__setup_cpu_power7)
 _GLOBAL(__restore_cpu_power7)
 	/* place holder */
 	blr
+
+/*
+ * Get a minimal set of registers for our caller's nth caller.
+ * r3 = regs pointer, r5 = n.
+ */
+_GLOBAL(perf_arch_fetch_caller_regs)
+	mr	r6,r1
+	cmpwi	r5,0
+	mflr	r4
+	ble	2f
+	mtctr	r5
+1:	PPC_LL	r6,0(r6)
+	bdnz	1b
+	PPC_LL	r4,PPC_LR_STKOFF(r6)
+2:	PPC_LL	r7,0(r6)
+	PPC_LL	r7,PPC_LR_STKOFF(r7)
+	PPC_STL	r6,GPR1-STACK_FRAME_OVERHEAD(r3)
+	PPC_STL	r4,_NIP-STACK_FRAME_OVERHEAD(r3)
+	PPC_STL	r7,_LINK-STACK_FRAME_OVERHEAD(r3)
+	blr