perf/x86/intel: Discard zero length call entries in LBR call stack
authorYan, Zheng <zheng.z.yan@intel.com>
Wed, 5 Nov 2014 02:56:11 +0000 (21:56 -0500)
committerIngo Molnar <mingo@kernel.org>
Wed, 18 Feb 2015 16:16:14 +0000 (17:16 +0100)
"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.

We can partially resolve this issue by: decode call instructions and
discard any zero length call entry in the LBR stack.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Signed-off-by: Kan Liang <kan.liang@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: eranian@google.com
Cc: jolsa@redhat.com
Link: http://lkml.kernel.org/r/1415156173-10035-16-git-send-email-kan.liang@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
arch/x86/kernel/cpu/perf_event_intel_lbr.c

index 92a44fd..084f2eb 100644 (file)
@@ -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)
@@ -702,6 +705,12 @@ 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;