Record a backtrace in the sampler

c8244ea7 · Silas Boyd-Wickizer · 7d71762b · c8244ea7 · c8244ea7
--- a/include/sampler.h
+++ b/include/sampler.h
@@ -6,8 +6,11 @@ struct sampconf {
  u64 period;
 };
+#define NTRACE 4
 struct pmuevent {
  u64 rip;
+  uptr trace[NTRACE];
 };
 struct logheader {

--- a/kernel/sampler.cc
+++ b/kernel/sampler.cc
@@ -95,12 +95,16 @@ static int
 samplog(struct trapframe *tf)
 {
  struct pmulog *l;
+  struct pmuevent *e;
  l = &pmulog[mycpu()->id];
  if (l->count == l->capacity)
    return 0;
-  l->event[l->count].rip = tf->rip;
+  e = &l->event[l->count];
+  e->rip = tf->rip;
+  getcallerpcs((void*)tf->rbp, e->trace, NELEM(e->trace));
  l->count++;
  return 1;
 }