Windows: Launcher doesn't work if argv[0] isn't set to the executable filename

[phst]

Description of the problem / feature request:

https://github.com/bazelbuild/bazel/blob/6.0.0-pre.20211110.1/src/tools/launcher/launcher_main.cc#L39 uses argv[0] to read information from the launcher binary, but argv[0] can be set arbitrarily by callers.

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

Create a Bazel workspace on Windows with the following files:

• WORKSPACE must be present, but can be empty
• BUILD:

  py_binary(name='bin',srcs=['bin.py'])
  

• bin.py:

  print('hello world')
  

• launch.py:

  #!/usr/bin/env python3
  import subprocess
  subprocess.run(['something'], executable='./bazel-bin/bin.exe', check=True)
  

Then, build the Python binary with bazel build :bin and run the launcher script using python launch.py. It will print an error:

LAUNCHER ERROR: Cannot open the binary to read launch data
LAUNCHER ERROR: Failed to parse launch info.
Traceback (most recent call last):
File "C:\Users\p\bazel-launcher-argv\launch.py", line 3, in
subprocess.run(['something'], executable='./bazel-bin/bin.exe', check=True)
File "C:\Program Files\Python39\lib\subprocess.py", line 528, in run
raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['something']' returned non-zero exit status 1.

The problem is that https://github.com/bazelbuild/bazel/blob/6.0.0-pre.20211110.1/src/tools/launcher/launcher_main.cc#L39 uses argv[0], it should use GetModuleFileNameW instead to obtain the actual executable filename.

This may seem exotic, but setting argv[0] to an arbitrary value is valid and supported. Also see the discussion at https://docs.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-createprocessw#parameters.

A Bazel-specific problem is that https://docs.google.com/document/d/e/2PACX-1vSDIrFnFvEYhKsCMdGdD40wZRBX3m3aZ5HhVj4CtHPmiXKDCxioTUbYsDydjKtFDAzER5eg7OjJWs3V/pub (implemented for the launcher in https://github.com/bazelbuild/bazel/pull/12650/files#diff-8632bef7ce05c706d0a109e19947e78a1ac4e029409fd4c32dc2ca1d3f1d7fdf) mandates checking argv[0] first for runfiles, and tools depending on tools (https://docs.bazel.build/versions/4.2.1/skylark/rules.html#tools-depending-on-tools) or binaries run as data dependencies at runtime/test time might inadvertedly pick the wrong runfile tree if argv[0] isn't set to the filename of the top-level tool. Following the recommendation at https://docs.bazel.build/versions/4.2.1/skylark/rules.html#tools-depending-on-tools ("it’s recommended that each subtool optionally accept its runfiles root as a parameter") addresses this, but it's somewhat awkward and requires all tools involved to cooperate.

What operating system are you running Bazel on?

Microsoft Windows [Version 10.0.17763.2300]

What's the output of bazel info release?

release 4.2.1

(I guess this issue is present in all versions.)

Have you found anything relevant by searching the web?

https://docs.microsoft.com/en-us/windows/win32/api/libloaderapi/nf-libloaderapi-getmodulefilenamew

Going forward, it might be better to use the resource functions (e.g. https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-loadstringw) instead.