First failing build is https://ci.chromium.org/buildbot/chromium.memory/Linux%20CFI/8387, but that's where Nico added mojo_core_unittests to the bot.

The report itself is as follows:

../../mojo/public/c/system/thunks.cc:71:5: runtime error: control flow integrity check for type 'void (MojoSystemThunks *)' failed during indirect function call
(libmojo_core.so+0x6a580): note: (unknown) defined here
    #0 0x53a19e  (/b/s/w/ir/out/Release/mojo_core_unittests+0x53a19e)
    #1 0x539d1c  (/b/s/w/ir/out/Release/mojo_core_unittests+0x539d1c)
    #2 0x3a2cef  (/b/s/w/ir/out/Release/mojo_core_unittests+0x3a2cef)
    #3 0x7fefa5119f44  (/lib/x86_64-linux-gnu/libc.so.6+0x21f44)
    #4 0x382029  (/b/s/w/ir/out/Release/mojo_core_unittests+0x382029)

Error: failed to symbolize snippets in JSON:

Traceback (most recent call last):
  File "/b/s/w/ir/tools/valgrind/asan/asan_symbolize.py", line 245, in <module>
    main()
  File "/b/s/w/ir/tools/valgrind/asan/asan_symbolize.py", line 238, in main
    symbolize_snippets_in_json(args.test_summary_json_file, loop)
  File "/b/s/w/ir/tools/valgrind/asan/asan_symbolize.py", line 194, in symbolize_snippets_in_json
    with open(filename, 'r') as f:
IOError: [Errno 2] No such file or directory: '/b/s/w/iofN02Bb/output.json'

Traceback (most recent call last):
  File "../../testing/test_env.py", line 280, in <module>
    sys.exit(main())
  File "../../testing/test_env.py", line 276, in main
    return run_executable(sys.argv[1:], os.environ.copy())
  File "../../testing/test_env.py", line 266, in run_executable
    symbolize_snippets_in_json(cmd, env)
  File "../../testing/test_env.py", line 172, in symbolize_snippets_in_json
    raise subprocess.CalledProcessError(p.returncode, symbolize_command)
subprocess.CalledProcessError: Command '['/b/s/w/ir/.swarming_module_cache/vpython/73deba/bin/python', '/b/s/w/ir/tools/valgrind/asan/asan_symbolize.py', '--test-summary-json-file=/b/s/w/iofN02Bb/output.json', '--executable-path=./mojo_core_unittests']' returned non-zero exit status 1