Record maps per process rather than globally, attempt #2

Rather than reading the PID off the bitcasted structure pointer, we need
to use the NewE parsed event instead to avoid struct offsets being
incorrect in case some fields are not present.

Also refactor the readEvent method to have less variable shadowing and
get rid of the pointless definition of E from the PERF_RECORD_SAMPLE
case.

Change-Id: I2cbaf91d5096acdb156ca83291626f134273cb91

Author: georges-arm

lnt/testing/profile/cPerf.cpp

@@ -855,8 +855,8 @@ void PerfReader::registerNewMapping(unsigned char *Buf, const char *Filename) {
 }
 
 unsigned char *PerfReader::readEvent(unsigned char *Buf) {
-  perf_event_header *E = (perf_event_header *)Buf;
-  switch (E->type) {
+  perf_event_header *Header = (perf_event_header *)Buf;
+  switch (Header->type) {
   case PERF_RECORD_MMAP:
   {
     perf_event_mmap *E = (perf_event_mmap *)Buf;
@@ -873,16 +873,15 @@ unsigned char *PerfReader::readEvent(unsigned char *Buf) {
   break;
   case PERF_RECORD_SAMPLE:
   {
-    perf_event_sample* E = (perf_event_sample*)Buf;
-    auto NewE = parseEvent(((unsigned char*)E) + sizeof(perf_event_header),
+    auto NewE = parseEvent(Buf + sizeof(perf_event_header),
                            EventLayouts.begin()->second);
     auto EventID = NewE.id;
     auto PC = NewE.ip;
 
     // Search for the map corresponding to this sample. Search backwards through
     // time, discarding any maps created after our timestamp.
     uint64_t MapID = ~0ULL;
-    auto &MapsForPid = CurrentMaps[E->pid];
+    auto &MapsForPid = CurrentMaps[NewE.pid];
     for (auto I = MapsForPid.rbegin(), E = MapsForPid.rend(); I != E; ++I) {
       if (I->first > NewE.time)
         continue;
@@ -907,7 +906,7 @@ unsigned char *PerfReader::readEvent(unsigned char *Buf) {
   }
   break;
   }
-  return &Buf[E->size];
+  return &Buf[Header->size];
 }
 
 perf_event_sample PerfReader::parseEvent(unsigned char *Buf, uint64_t Layout) {