2 files changed, 30 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/asm-compat.h b/arch/powerpc/include/asm/asm-compat.h
index c1b475a941eb..a9b91ed3d4b9 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 2d29752cbe16..b485a87c94e1 100644
--- a/arch/powerpc/kernel/misc.S
+++ b/arch/powerpc/kernel/misc.S
@@ -127,3 +127,31 @@ _GLOBAL(__setup_cpu_power7)
 _GLOBAL(__restore_cpu_power7)
         /* place holder */
         blr
+
+#ifdef CONFIG_EVENT_TRACING
+/*
+ * Get a minimal set of registers for our caller's nth caller.
+ * r3 = regs pointer, r5 = n.
+ *
+ * We only get R1 (stack pointer), NIP (next instruction pointer)
+ * and LR (link register).  These are all we can get in the
+ * general case without doing complicated stack unwinding, but
+ * fortunately they are enough to do a stack backtrace, which
+ * is all we need them for.
+ */
+_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
+#endif /* CONFIG_EVENT_TRACING */