[HWASan] Improve symbol indexing (#135967)

Previously we would add any ELF that contained a build id regardless
whether the ELF contained symbols or not. This works for Android since
soong will strip the symbols into a new directory. However other
build systems, like BUCK, will write the stripped file in the same
directory as the unstripped file. This would cause the hwasan_symbolize
script sometimes add then stripped ELF to its index and ignore the
symbolized ELF. The logic has now been changed to only add ELFs that
contain symbols to the index. If two symbolized ELFs are encountered
with the same build id, we now exit out with an error.

Fixes #135966

---------

Co-authored-by: Stefan Bossbaly <sboss@meta.com>

compiler-rt/lib/hwasan/scripts/hwasan_symbolize

@@ -16,6 +16,7 @@ from __future__ import unicode_literals
 
 import argparse
 import glob
+import hashlib
 import html
 import json
 import mmap
@@ -37,8 +38,9 @@ if sys.version_info.major < 3:
 Ehdr_size = 64
 e_shnum_offset = 60
 e_shoff_offset = 40
-
+e_shstrndx_offset = 62
 Shdr_size = 64
+sh_name_offset = 0
 sh_type_offset = 4
 sh_offset_offset = 24
 sh_size_offset = 32
@@ -62,13 +64,32 @@ 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 handle_shstrtab(mv, e_shoff):
+  e_shstrndx, = struct.unpack_from('<H', buffer=mv, offset=e_shstrndx_offset)
+  
+  start_shstrndx = e_shoff + e_shstrndx * Shdr_size
+  shstrndx_sh = mv[start_shstrndx: start_shstrndx + Shdr_size]
+  _, shstrndx_sh_offset, shstrndx_sh_size = handle_Shdr(shstrndx_sh)
+  return mv[shstrndx_sh_offset:shstrndx_sh_offset + shstrndx_sh_size]
+
+def read_string(mv):
+  name = ""
+  for byte in mv:
+    char = chr(byte)
+    if char == '\x00':
+      break
+    name += char
+  return name
+
+def unpack_sh_type(mv):
   sh_type, = struct.unpack_from('<I', buffer=mv, offset=sh_type_offset)
-  if sh_type != SHT_NOTE:
-    return None, None
+  return sh_type
+
+def handle_Shdr(mv):
+  name_offset, = struct.unpack_from('<I', buffer=mv, offset=sh_name_offset)
   sh_offset, = struct.unpack_from('<Q', buffer=mv, offset=sh_offset_offset)
   sh_size, = struct.unpack_from('<Q', buffer=mv, offset=sh_size_offset)
-  return sh_offset, sh_size
+  return name_offset, sh_offset, sh_size
 
 def handle_elf(mv):
   # \x02 is ELFCLASS64, \x01 is ELFDATA2LSB. HWASan currently only works on
@@ -76,19 +97,37 @@ 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)
+
+  # Section where all the section header names are stored.
+  shstr = handle_shstrtab(mv, e_shoff)
+
   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_name_offset, sh_offset, sh_size = handle_Shdr(sh)
+    sh_name = read_string(shstr[sh_name_offset:])
+    sh_type = unpack_sh_type(sh)
 
-def get_buildid(filename):
+    if sh_name == ".debug_info":
+      found_symbols = True
+    if sh_type == SHT_NOTE:
+      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
+
+  if found_symbols:
+    return bid
+  else:
+    return None
+
+def read_elf(filename):
   with open(filename, "r") as fd:
     if os.fstat(fd.fileno()).st_size < Ehdr_size:
       return None
@@ -200,7 +239,7 @@ 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 +307,30 @@ class Symbolizer:
         for fn in fnames:
           filename = os.path.join(dname, fn)
           try:
-            bid = get_buildid(filename)
+            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 bid is None:
+            continue
+
+          if bid in self.__index:
+            index_filename = self.__index[bid]
+
+            if os.path.samefile(index_filename, filename):
+              continue
+
+            with open(filename, "rb") as f:
+              file_hash = hashlib.file_digest(f, "sha256")
+
+            with open(index_filename, "rb") as f:
+              index_file_hash = hashlib.file_digest(f, "sha256")
+
+            if index_file_hash.digest() != file_hash.digest():
+              print("Build ID collision! Files share the same BuildId ({}) but their contents differ. Files {} and {} ".format(bid, filename, index_filename), file=sys.stderr)
+          else:
             self.__index[bid] = filename
 
   def symbolize_line(self, line):