[PATCH v2 7/7] perf, x86: Discard zero length call entries in LBR call stack

2013-07-01 Thread Yan, Zheng 
From: "Yan, Zheng" 

"Zero length call" uses the attribute of the call instruction to push
the immediate instruction pointer on to the stack and then pops off
that address into a register. This is accomplished without any matching
return instruction. It confuses the hardware and make the recorded call
stack incorrect. Try fixing the call stack by discarding zero length
call entries.

Signed-off-by: Yan, Zheng 
---
 arch/x86/kernel/cpu/perf_event_intel_lbr.c | 13 +++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c 
b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index 3146fb5..b1617d8 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -94,7 +94,8 @@ enum {
X86_BR_ABORT= 1 << 12,/* transaction abort */
X86_BR_IN_TX= 1 << 13,/* in transaction */
X86_BR_NO_TX= 1 << 14,/* not in transaction */
-   X86_BR_CALL_STACK   = 1 << 15,/* call stack */
+   X86_BR_ZERO_CALL= 1 << 15,/* zero length call */
+   X86_BR_CALL_STACK   = 1 << 16,/* call stack */
 };
 
 #define X86_BR_PLM (X86_BR_USER | X86_BR_KERNEL)
@@ -111,13 +112,15 @@ enum {
 X86_BR_JMP  |\
 X86_BR_IRQ  |\
 X86_BR_ABORT|\
-X86_BR_IND_CALL)
+X86_BR_IND_CALL |\
+X86_BR_ZERO_CALL)
 
 #define X86_BR_ALL (X86_BR_PLM | X86_BR_ANY)
 
 #define X86_BR_ANY_CALL \
(X86_BR_CALL|\
 X86_BR_IND_CALL|\
+X86_BR_ZERO_CALL   |\
 X86_BR_SYSCALL |\
 X86_BR_IRQ |\
 X86_BR_INT)
@@ -650,6 +653,12 @@ static int branch_type(unsigned long from, unsigned long 
to, int abort)
ret = X86_BR_INT;
break;
case 0xe8: /* call near rel */
+   insn_get_immediate(&insn);
+   if (insn.immediate1.value == 0) {
+   /* zero length call */
+   ret = X86_BR_ZERO_CALL;
+   break;
+   }
case 0x9a: /* call far absolute */
ret = X86_BR_CALL;
break;
-- 
1.8.1.4

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Re: [PATCH V2 7/7] perf, x86: Discard zero length call entries in LBR call stack

2012-10-25 Thread Namhyung Kim 
Hi,

On Wed, 24 Oct 2012 13:59:10 +0800, Zheng Yan wrote:
> From: "Yan, Zheng" 
>
> Zero length calls may confuse the hardware and make the recorded
> call stack incorrect. Try fixing the call stack by discarding
> zero length call entries.

It would be great adding an explanation what is the "zero length call"
and why it makes a confusion.

Thanks,
Namhyung
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[PATCH V2 7/7] perf, x86: Discard zero length call entries in LBR call stack

2012-10-23 Thread Yan, Zheng 
From: "Yan, Zheng" 

Zero length calls may confuse the hardware and make the recorded
call stack incorrect. Try fixing the call stack by discarding
zero length call entries.

Signed-off-by: Yan, Zheng 
---
 arch/x86/kernel/cpu/perf_event_intel_lbr.c | 13 +++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c 
b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
index 4879904..012ddca 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
@@ -86,7 +86,8 @@ enum {
X86_BR_ABORT= 1 << 12,/* transaction abort */
X86_BR_INTX = 1 << 13,/* in transaction */
X86_BR_NOTX = 1 << 14,/* not in transaction */
-   X86_BR_CALL_STACK   = 1 << 15,/* call stack */
+   X86_BR_ZERO_CALL= 1 << 15,/* zero length call */
+   X86_BR_CALL_STACK   = 1 << 16,/* call stack */
 };
 
 #define X86_BR_PLM (X86_BR_USER | X86_BR_KERNEL)
@@ -103,13 +104,15 @@ enum {
 X86_BR_JMP  |\
 X86_BR_IRQ  |\
 X86_BR_ABORT|\
-X86_BR_IND_CALL)
+X86_BR_IND_CALL |\
+X86_BR_ZERO_CALL)
 
 #define X86_BR_ALL (X86_BR_PLM | X86_BR_ANY)
 
 #define X86_BR_ANY_CALL \
(X86_BR_CALL|\
 X86_BR_IND_CALL|\
+X86_BR_ZERO_CALL   |\
 X86_BR_SYSCALL |\
 X86_BR_IRQ |\
 X86_BR_INT)
@@ -625,6 +628,12 @@ static int branch_type(unsigned long from, unsigned long 
to, int abort)
ret = X86_BR_INT;
break;
case 0xe8: /* call near rel */
+   insn_get_immediate(&insn);
+   if (insn.immediate1.value == 0) {
+   /* zero length call */
+   ret = X86_BR_ZERO_CALL;
+   break;
+   }
case 0x9a: /* call far absolute */
ret = X86_BR_CALL;
break;
-- 
1.7.11.7

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