[lldb/test] Don't use preexec_fn for launching inferiors

As the documentation states, using this is not safe in multithreaded
programs, and I have traced it to a rare deadlock in some of the tests.

The reason this was introduced was to be able to attach to a program
from the very first instruction, where our usual mechanism of
synchronization -- waiting for a file to appear -- does not work.

However, this is only needed for a single test
(TestGdbRemoteAttachWait) so instead of doing this everywhere, I create
a bespoke solution for that single test. The solution basically
consists of outsourcing the preexec_fn code to a separate (and
single-threaded) shim process, which enables attaching and then executes
the real program.

This pattern could be generalized in case we needed to use it for other
tests, but I suspect that we will not be having many tests like this.

This effectively reverts commit
a997a1d7fbe229433fb458bb0035b32424ecf3bd.

2 files changed, 1 insertions, 14 deletions

diff --git a/lldb/packages/Python/lldbsuite/test/lldbplatformutil.py b/lldb/packages/Python/lldbsuite/test/lldbplatformutil.py
index e14c4f8..719131c 100644
--- a/lldb/packages/Python/lldbsuite/test/lldbplatformutil.py
+++ b/lldb/packages/Python/lldbsuite/test/lldbplatformutil.py
@@ -4,12 +4,11 @@ architecture and/or the platform dependent nature of the tests. """
 from __future__ import absolute_import
 
 # System modules
-import ctypes
 import itertools
-import os
 import re
 import subprocess
 import sys
+import os
 
 # Third-party modules
 import six
@@ -192,14 +191,3 @@ def hasChattyStderr(test_case):
     if match_android_device(test_case.getArchitecture(), ['aarch64'], range(22, 25+1)):
         return True  # The dynamic linker on the device will complain about unknown DT entries
     return False
-
-if getHostPlatform() == "linux":
-    def enable_attach():
-        """Enable attaching to _this_ process, if host requires such an action.
-        Suitable for use as a preexec_fn in subprocess.Popen and similar."""
-        c = ctypes.CDLL(None)
-        PR_SET_PTRACER = ctypes.c_int(0x59616d61)
-        PR_SET_PTRACER_ANY = ctypes.c_ulong(-1)
-        c.prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY)
-else:
-    enable_attach = None
diff --git a/lldb/packages/Python/lldbsuite/test/lldbtest.py b/lldb/packages/Python/lldbsuite/test/lldbtest.py
index 2285173..d46e54f 100644
--- a/lldb/packages/Python/lldbsuite/test/lldbtest.py
+++ b/lldb/packages/Python/lldbsuite/test/lldbtest.py
@@ -393,7 +393,6 @@ class _LocalProcess(_BaseProcess):
             stdout=open(
                 os.devnull) if not self._trace_on else None,
             stdin=PIPE,
-            preexec_fn=lldbplatformutil.enable_attach,
             env=env)
 
     def terminate(self):