[LNT] Fixed possible crash or junk data in cPerf

The return value of the first call of Dump.next() was not checked. Dump.getText() returned an uninitialized string (a junk string) if the objdump did not return an usable data for the specified address range. It caused a crash or inconsistent profile data.

OS Laboratory. Huawei Russian Research Institute. Saint-Petersburg

Reviewed By: thopre

Differential Revision: https://reviews.llvm.org/D112782

Author: Pavel Kosov

lnt/testing/profile/cPerf.cpp

@@ -365,6 +365,7 @@ class ObjdumpOutput {
 
   void reset(Map *M, uint64_t Start, uint64_t Stop) {
     ThisAddress = 0;
+    ThisText = "";
     if (Stream) {
       fclose(Stream);
       wait(NULL);
@@ -396,6 +397,7 @@ class ObjdumpOutput {
       ssize_t Len = getline(&Line, &LineLen, Stream);
       if (Len == -1) {
         ThisAddress = EndAddress;
+        ThisText = "";
         return;
       }
       char *TokBuf;
@@ -757,10 +759,9 @@ void PerfReader::emitSymbol(
     uint64_t Adjust) {
   ObjdumpOutput Dump(Objdump, BinaryCacheRoot);
   Dump.reset(&M, Sym.Start, Sym.End);
-  Dump.next();
 
   emitFunctionStart(Sym.Name);
-  for (uint64_t I = Sym.Start; I < Sym.End; I = Dump.next()) {
+  for (uint64_t I = Dump.next(); I < Sym.End; I = Dump.next()) {
     auto PC = Event->first - Adjust;
 
     auto Text = Dump.getText();