gh-127076: Disable strace tests under LD_PRELOAD (#127086)

Distribution tooling (ex. sandbox on Gentoo and fakeroot on Debian) uses
LD_PRELOAD to intercept system calls and potentially modify them when
building. These tools can change the set of system calls, so disable
system call testing under these cases.

Co-authored-by: Michał Górny <mgorny@gentoo.org>

Lib/test/support/strace_helper.py

@@ -1,6 +1,7 @@
 import re
 import sys
 import textwrap
+import os
 import unittest
 from dataclasses import dataclass
 from functools import cache
@@ -163,6 +164,13 @@ def requires_strace():
     if sys.platform != "linux":
         return unittest.skip("Linux only, requires strace.")
 
+    if "LD_PRELOAD" in os.environ:
+        # Distribution packaging (ex. Debian `fakeroot` and Gentoo `sandbox`)
+        # use LD_PRELOAD to intercept system calls, which changes the overall
+        # set of system calls which breaks tests expecting a specific set of
+        # system calls).
+        return unittest.skip("Not supported when LD_PRELOAD is intercepting system calls.")
+
     if support.check_sanitizer(address=True, memory=True):
         return unittest.skip("LeakSanitizer does not work under ptrace (strace, gdb, etc)")
 

Misc/NEWS.d/next/Tests/2024-11-21-02-03-48.gh-issue-127076.a3avV1.rst

@@ -0,0 +1 @@
+Disable strace based system call tests when LD_PRELOAD is set.