ivtest: Detect execution errors in vvp_reg.py

Currently vvp_reg.py uses `returncode >= 256` to distinguish execution
errors from ordinary compile or simulation failures. That matches the encoded
status returned by wait(), but subprocess.run() does not expose that value. Its
returncode is the decoded process exit status, or `-N` if the process was
terminated by signal N. Shell wrappers can also report signal termination as
`128 + N`.

As a result a compiler crash can be reported as `-11` or `139`. Both values
pass the old check and a CE test can be accepted as a normal compiler error.

Treat negative return codes and return codes greater than or equal to 128 as
execution errors before accepting CE and EF results. Also make sure that CE gold
mismatches are reported as failures.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>

ivtest/run_ivl.py

@@ -129,6 +129,10 @@ def run_cmd(cmd: list) -> subprocess.CompletedProcess:
     res = subprocess.run(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, check=False)
     return res
 
+def is_execution_error(returncode: int) -> bool:
+    '''Check if a command failed due to an execution error.'''
+    return returncode < 0 or returncode >= 128
+
 
 # pylint: disable-next=invalid-name
 def run_CE(options: dict, cfg: dict) -> list:
@@ -154,10 +158,12 @@ def run_CE(options: dict, cfg: dict) -> list:
 
     if res.returncode == 0:
         return [1, "Failed - CE (no error reported)."]
-    if res.returncode >= 256:
+    if is_execution_error(res.returncode):
         return [1, "Failed - CE (execution error)."]
-    if options['gold'] is not None and not check_gold(options, log_list):
-        return [1, "Failed - CE (Gold file doesn't match output)."]
+    if options['gold'] is not None:
+        gold_rtn = check_gold(options, log_list)
+        if gold_rtn[0]:
+            return [1, "Failed - CE (Gold file doesn't match output)."]
     return [0, "Passed - CE."]
 
 
@@ -248,6 +254,8 @@ def options_to_pass(options: dict) -> list:
 
 def build_ivl_return(translation_fail: bool, res: subprocess.CompletedProcess) -> list:
     '''Generate the return for the iverilog run.'''
+    if is_execution_error(res.returncode):
+        return [1, "Failed - iverilog execution error."]
     if translation_fail:
         if res.returncode != 0:
             return [0, "Passed - TE."]
@@ -258,11 +266,11 @@ def build_ivl_return(translation_fail: bool, res: subprocess.CompletedProcess) -
 
 def build_vvp_return(expected_fail: bool, res: subprocess.CompletedProcess) -> list:
     '''Generate the return for the vvp run.'''
+    if is_execution_error(res.returncode):
+        return [1, "Failed - vvp execution error"]
     if res.returncode != 0 and expected_fail:
         return [0, "Passed - EF."]
-    if res.returncode >= 256:
-        return [1, "Failed - vvp execution error"]
-    if res.returncode > 0 and res.returncode < 256 and not expected_fail:
+    if res.returncode > 0 and not expected_fail:
         return [1, "Failed - vvp error, but expected to succeed"]
     return []