[Qemu-devel] Counting barrier instructions in ARM

[Pranith Kumar <bobby.prani@gmail.com>]

Hello,

I am trying to count the number of barrier instructions (dmb) which are being
executed in an multi-threaded ARM executable. I am running the executable using
qemu user mode with the following patch applied.

Basically I created two counters in the ARM cpu state and incrementing them by
generating a TCG instruction whenever a barrier instruction is translated. I am
doing something similar even for counting the total instructions executed.

The problem I am facing is that this seems to be crashing when run with a
multi-threaded executable. Also the statistics gathered are not really accurate.

Is there something obviously wrong with what I am trying to do? Any help is
highly appreciated.

Thanks!


---
 linux-user/main.c      | 10 +++++++++-
 target-arm/cpu.h       |  2 ++
 target-arm/translate.c |  9 +++++++++
 3 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/linux-user/main.c b/linux-user/main.c
index b453a39..7984027 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -816,7 +816,15 @@ void cpu_loop(CPUARMState *env)
                             break;
                         }
                     } else {
-                        env->regs[0] = do_syscall(env,
+            // print stats on exit
+            if (n == 248) {
+                FILE *icount_file = fopen("inscount.out", "w");
+                unsigned long total  = (unsigned long)env->fence_count;
+                unsigned long icount = (unsigned long)env->insn_count;
+                fprintf(icount_file, "%lu, %lu, %f\n", icount, total, total * 1000.0/icount);
+                fclose(icount_file);
+            }
+            env->regs[0] = do_syscall(env,
                                                   n,
                                                   env->regs[0],
                                                   env->regs[1],
diff --git a/target-arm/cpu.h b/target-arm/cpu.h
index 369d472..be38574 100644
--- a/target-arm/cpu.h
+++ b/target-arm/cpu.h
@@ -304,6 +304,8 @@ typedef struct CPUARMState {
     uint64_t exclusive_test;
     uint32_t exclusive_info;
 #endif
+    uint32_t fence_count;
+    uint32_t insn_count;
 
     /* iwMMXt coprocessor state.  */
     struct {
diff --git a/target-arm/translate.c b/target-arm/translate.c
index cf4e767..4d4ceb1 100644
--- a/target-arm/translate.c
+++ b/target-arm/translate.c
@@ -68,6 +68,8 @@ static TCGv_i64 cpu_exclusive_val;
 static TCGv_i64 cpu_exclusive_test;
 static TCGv_i32 cpu_exclusive_info;
 #endif
+static TCGv_i32 cpu_fence_count;
+static TCGv_i32 cpu_insn_count;
 
 /* FIXME:  These should be removed.  */
 static TCGv_i32 cpu_F0s, cpu_F1s;
@@ -106,6 +108,10 @@ void arm_translate_init(void)
     cpu_exclusive_info = tcg_global_mem_new_i32(TCG_AREG0,
         offsetof(CPUARMState, exclusive_info), "exclusive_info");
 #endif
+    cpu_fence_count = tcg_global_mem_new_i32(TCG_AREG0,
+            offsetof(CPUARMState, fence_count), "fence_count");
+    cpu_insn_count = tcg_global_mem_new_i32(TCG_AREG0,
+            offsetof(CPUARMState, insn_count), "insn_count");
 
     a64_translate_init();
 }
@@ -7568,6 +7574,7 @@ static void disas_arm_insn(CPUARMState * env, DisasContext *s)
             case 5: /* dmb */
             case 6: /* isb */
                 ARCH(7);
+        tcg_gen_add_i32(cpu_fence_count, cpu_fence_count, 1);
                 /* We don't emulate caches so these are a no-op.  */
                 return;
             default:
@@ -9740,6 +9747,7 @@ static int disas_thumb2_insn(CPUARMState *env, DisasContext *s, uint16_t insn_hw
                         case 4: /* dsb */
                         case 5: /* dmb */
                         case 6: /* isb */
+                tcg_gen_add_i32(cpu_fence_count, cpu_fence_count, 1);
                             /* These execute as NOPs.  */
                             break;
                         default:
@@ -11022,6 +11030,7 @@ static inline void gen_intermediate_code_internal(ARMCPU *cpu,
             tcg_gen_debug_insn_start(dc->pc);
         }
 
+    tcg_gen_add_i32(cpu_insn_count, cpu_insn_count, 1);
         if (dc->thumb) {
             disas_thumb_insn(env, dc);
             if (dc->condexec_mask) {
-- 
1.9.1