[HWASan] Fix symbol indexing

compiler-rt/lib/hwasan/scripts/hwasan_symbolize

@@ -42,6 +42,7 @@ Shdr_size = 64
 sh_type_offset = 4
 sh_offset_offset = 24
 sh_size_offset = 32
+SHT_SYMTAB = 2
 SHT_NOTE = 7
 
 Nhdr_size = 12
@@ -62,8 +63,13 @@ def handle_Nhdr(mv, sh_size):
     offset += Nhdr_size + align_up(n_namesz, 4) + align_up(n_descsz, 4)
   return None
 
-def handle_Shdr(mv):
+def unpack_sh_type(mv):
   sh_type, = struct.unpack_from('<I', buffer=mv, offset=sh_type_offset)
+  return sh_type
+
+def handle_Shdr(mv):
+  sh_type = unpack_sh_type(mv)
+  # Sanity check
   if sh_type != SHT_NOTE:
     return None, None
   sh_offset, = struct.unpack_from('<Q', buffer=mv, offset=sh_offset_offset)
@@ -76,19 +82,29 @@ def handle_elf(mv):
   # have to extend the parsing code.
   if mv[:6] != b'\x7fELF\x02\x01':
     return None
+  found_symbols = False
+  bid = None
   e_shnum, = struct.unpack_from('<H', buffer=mv, offset=e_shnum_offset)
   e_shoff, = struct.unpack_from('<Q', buffer=mv, offset=e_shoff_offset)
   for i in range(0, e_shnum):
     start = e_shoff + i * Shdr_size
-    sh_offset, sh_size = handle_Shdr(mv[start: start + Shdr_size])
-    if sh_offset is None:
-      continue
-    note_hdr = mv[sh_offset: sh_offset + sh_size]
-    result = handle_Nhdr(note_hdr, sh_size)
-    if result is not None:
-      return result
+    sh = mv[start: start + Shdr_size]
+    sh_type = unpack_sh_type(sh)
+
+    if sh_type == SHT_SYMTAB:
+      found_symbols = True
+    elif sh_type == SHT_NOTE:
+      sh_offset, sh_size = handle_Shdr(sh)
+      if sh_offset is None:
+        continue
+      note_hdr = mv[sh_offset: sh_offset + sh_size]
+      result = handle_Nhdr(note_hdr, sh_size)
+      if result is not None:
+        bid = result
+
+  return (found_symbols, bid)
 
-def get_buildid(filename):
+def read_elf(filename):
   with open(filename, "r") as fd:
     if os.fstat(fd.fileno()).st_size < Ehdr_size:
       return None
@@ -200,7 +216,7 @@ class Symbolizer:
       if os.path.exists(full_path):
         return full_path
     if name not in self.__warnings:
-      print("Could not find symbols for", name, file=sys.stderr)
+      print("Could not find symbols for {} (Build ID: {})".format(name, buildid), file=sys.stderr)
       self.__warnings.add(name)
     return None
 
@@ -268,13 +284,16 @@ class Symbolizer:
         for fn in fnames:
           filename = os.path.join(dname, fn)
           try:
-            bid = get_buildid(filename)
+            found_symbols, bid = read_elf(filename)
           except FileNotFoundError:
             continue
           except Exception as e:
             print("Failed to parse {}: {}".format(filename, e), file=sys.stderr)
             continue
-          if bid is not None:
+          if found_symbols and bid is not None:
+            if bid in self.__index:
+              print("Duplicate build ID {} for {} and {}".format(bid, self.__index[bid], filename), file=sys.stderr)
+              sys.exit(1)
             self.__index[bid] = filename
 
   def symbolize_line(self, line):