Switch to measuring CPU time instead of real time in test timeouts

Signed-off-by: Artur Bieniek <abieniek@internships.antmicro.com>

test_regress/driver.py

@@ -4,6 +4,7 @@
 
 import argparse
 import collections
+import ctypes
 import glob
 import hashlib
 import json
@@ -14,6 +15,7 @@ import pickle
 import platform
 import pty
 import re
+import resource
 import runpy
 import shutil
 import signal
@@ -1366,6 +1368,19 @@ class VlTest:
             ]
             self.run(logfile=self.obj_dir + "/pli_compile.log", fails=param['fails'], cmd=cmd)
 
+    def timeout(self, seconds):
+        """Limit the CPU time of the test - this limit is inherited
+        by all of the spawned child processess"""
+        #  An  unprivileged  process may set only its soft limit
+        #  to a value in the range from 0 up to the hard limit
+        _, hardlimit = resource.getrlimit(resource.RLIMIT_CPU)
+        softlimit = ctypes.c_long(min(seconds, ctypes.c_ulong(hardlimit).value)).value
+        # Casting is required due to a quirk in Python,
+        # rlimit values are interpreted as LONG, instead of ULONG
+        # https://github.com/python/cpython/issues/137044
+        rlimit = (softlimit, hardlimit)
+        resource.setrlimit(resource.RLIMIT_CPU, rlimit)
+
     def execute(self, **kwargs) -> None:
         """Run simulation executable.
         Arguments similar to run(); default arguments are from self"""

test_regress/t/t_concat_string.py

@@ -7,12 +7,11 @@
 # Version 2.0.
 # SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
 
-import signal
 import vltest_bootstrap
 
 test.scenarios('simulator')
 
-signal.alarm(15)  # 15s timeout
+test.timeout(15)
 
 test.compile()
 

test_regress/t/t_const_number_unsized_parse.py

@@ -7,7 +7,6 @@
 # Version 2.0.
 # SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
 
-import signal
 import vltest_bootstrap
 
 test.scenarios('vlt')
@@ -20,7 +19,7 @@ with open(test.top_filename, "w", encoding="utf8") as f:
         f.write(f"  int x{i} = 'd{i};\n")
     f.write("endmodule\n")
 
-signal.alarm(30)  # 30s timeout
+test.timeout(30)
 
 test.lint(verilator_flags2=[f"--max-num-width {2**29}"])
 

test_regress/t/t_timeout.py

@@ -0,0 +1,24 @@
+#!/usr/bin/env python3
+# DESCRIPTION: Verilator: Verilog Test driver/expect definition
+#
+# Copyright 2025 by Wilson Snyder. This program is free software; you
+# can redistribute it and/or modify it under the terms of either the GNU
+# Lesser General Public License Version 3 or the Perl Artistic License
+# Version 2.0.
+# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
+
+import vltest_bootstrap
+
+test.scenarios('dist')
+
+test.passes()
+
+test.timeout(1)
+
+# Check whether the soft limit is set to 1s
+test.run(cmd=["bash", "-c", "\"[ '$(ulimit -St)' -eq 1 ] || exit 1\""])
+
+# Set the hard limit to 2s (in case soft limit fails) and run a command which spins until signalled
+test.run(cmd=["bash", "-c", "\"trap 'exit 0' SIGXCPU; ulimit -Ht 2; while :; do :; done\""])
+
+test.passes()