SuperSize: Use the combined native library for analysis where needed

With native feature modules, generation of the main library (and feature
libraries) is a two-step process:

1. Link a single, combined library (with partitions inside it)
2. Use llvm-objcopy to split out the main lib and feature libs

This implies that:
- libchrome.so's ninja inputs are not .o and .a files
- The .map file now relates to the combined library, not the partitions,
  although it can naturally be used to analyze the partitions.

Bug: 982334
Change-Id: I345f618f30639e7637ee905776a50c9cf5686773
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1708204
Commit-Queue: Christopher Grant <cjgrant@chromium.org>
Reviewed-by: Samuel Huang <huangs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680169}

tools/binary_size/libsupersize/archive.py

@@ -1339,6 +1339,18 @@ def CreateSectionSizesAndSymbols(map_path=None,
     logging.info('Parsing ninja files.')
     source_mapper, ninja_elf_object_paths = (
         ninja_parser.Parse(output_directory, elf_path))
+
+    # If no symbols came from the library, it's because it's a partition
+    # extracted from a combined library. Look there instead.
+    if not ninja_elf_object_paths and elf_path:
+      combined_elf_path = elf_path.replace('.so', '__combined.so')
+      logging.info('Found no objects in %s, trying %s', elf_path,
+                   combined_elf_path)
+      source_mapper, ninja_elf_object_paths = (ninja_parser.Parse(
+          output_directory, combined_elf_path))
+      if ninja_elf_object_paths:
+        assert map_path and '__combined.so.map' in map_path
+
     logging.debug('Parsed %d .ninja files.', source_mapper.parsed_file_count)
     assert not elf_path or ninja_elf_object_paths, (
         'Failed to find link command in ninja files for ' +
@@ -1487,6 +1499,11 @@ def _SectionSizesFromElf(elf_path, tool_prefix):
   return section_sizes
 
 
+def _ElfIsMainPartition(elf_path, tool_prefix):
+  section_names = _SectionSizesFromElf(elf_path, tool_prefix).keys()
+  return models.SECTION_PART_END in section_names
+
+
 def _ArchFromElf(elf_path, tool_prefix):
   args = [path_util.GetReadElfPath(tool_prefix), '-h', elf_path]
   stdout = subprocess.check_output(args)
@@ -1653,13 +1670,21 @@ def _DeduceMainPaths(args, parser, extracted_minimal_apk_path=None):
     if not map_path.endswith('.map') and not map_path.endswith('.map.gz'):
       parser.error('Expected --map-file to end with .map or .map.gz')
   elif elf_path:
-    map_path = elf_path + '.map'
+    # Look for a .map file named for either the ELF file, or in the partitioned
+    # native library case, the combined ELF file from which the main library was
+    # extracted. Note that we don't yet have a tool_prefix to use here, but
+    # that's not a problem for this use case.
+    if _ElfIsMainPartition(elf_path, ''):
+      map_path = elf_path.replace('.so', '__combined.so') + '.map'
+    else:
+      map_path = elf_path + '.map'
     if not os.path.exists(map_path):
       map_path += '.gz'
     if not os.path.exists(map_path):
       parser.error('Could not find .map(.gz)? file. Ensure you have built with '
                    'is_official_build=true and generate_linker_map=true, or '
                    'use --map-file to point me a linker map file.')
+
   tool_prefix = None
   if map_path:
     linker_name = _DetectLinkerName(map_path)