[compiler-rt] [test] Handle missing ld.gold gracefully

[mgorny]

Summary

Fix the is_binutils_lto_supported() function to handle missing
executables gracefully. Currently, the function does not catch
exceptions from subprocess.Popen() and therefore causes lit to crash
if config.gold_executable does not specify a valid executable:

lit: /usr/lib/python3.11/site-packages/lit/TestingConfig.py:136: fatal: unable to parse config file '/tmp/portage/sys-libs/compiler-rt-
15.0.0/work/compiler-rt/test/lit.common.cfg.py', traceback: Traceback (most recent call last):
  File "/usr/lib/python3.11/site-packages/lit/TestingConfig.py", line 125, in load_from_path
    exec(compile(data, path, 'exec'), cfg_globals, None)
  File "/tmp/portage/sys-libs/compiler-rt-15.0.0/work/compiler-rt/test/lit.common.cfg.py", line 561, in <module>
    if is_binutils_lto_supported():
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/portage/sys-libs/compiler-rt-15.0.0/work/compiler-rt/test/lit.common.cfg.py", line 543, in is_binutils_lto_supported
    ld_cmd = subprocess.Popen([exe, '--help'], stdout=subprocess.PIPE, env={'LANG': 'C'})
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/subprocess.py", line 1022, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/usr/lib/python3.11/subprocess.py", line 1899, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'GOLD_EXECUTABLE-NOTFOUND'

[mgorny]

After reviewing this, please also approve backport to 15.x in https://github.com/llvm/llvm-project/issues/57580.

[MaskRay]

Python 3.7 can use subprocess.run with capture_output: https://docs.python.org/3/library/subprocess.html#:~:text=capture_output

But llvm-project requires Python >= 3.6 now, so we have to stay with Popen. Technically OSError can be FileNotFoundError if you want to be more specific.

[mgorny]

In D133358#3773210, @MaskRay wrote:

Python 3.7 can use subprocess.run with capture_output: https://docs.python.org/3/library/subprocess.html#:~:text=capture_output

Well, if you wanted to avoid calling subprocess.Popen(), then you could also use the "older" subprocess.check_output(). Not sure if using the "older" API should be a goal though.

Technically OSError can be FileNotFoundError if you want to be more specific.

I actually wanted a catch-all here. I don't think we want to crash if ld.gold e.g. isn't executable or something like that, we just care that we can't use it.

compiler-rt/test/lit.common.cfg.py

 
 def is_binutils_lto_supported():
   if not os.path.exists(os.path.join(config.llvm_shlib_dir, 'LLVMgold.so')):
     return False
 
   # We require both ld.bfd and ld.gold exist and support plugins. They are in
   # the same repository 'binutils-gdb' and usually built together.
   for exe in (config.gnu_ld_executable, config.gold_executable):
+    try:
       ld_cmd = subprocess.Popen([exe, '--help'], stdout=subprocess.PIPE, env={'LANG': 'C'})
       ld_out = ld_cmd.stdout.read().decode()
       ld_cmd.wait()
+    except OSError:
+      return False
     if not '-plugin' in ld_out:
       return False
 
   return True
 
 def is_windows_lto_supported():
   return os.path.exists(os.path.join(config.llvm_tools_dir, 'lld-link.exe'))