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PreserveImportsExportsJS fuzzer: Handle crashes and function ids #8648

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PreserveImportsExportsJS fuzzer: Handle crashes and function ids #8648

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075c07c
fix
kripken Apr 27, 2026
4fdf0ed
fix
kripken Apr 27, 2026
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14 changes: 13 additions & 1 deletion scripts/fuzz_opt.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2219,6 +2219,11 @@ def do_handle_pair(self, input, before_wasm, after_wasm, opts):
def do_run(self, vm, js, wasm):
out = vm.run_js(js, wasm, checked=False)

# VM crashes are actual issues we want to find.
if '(core dumped)' in out or 'Received signal' in out or '== C stack trace ==' in out or '== JS stack trace ==' in out:
raise Exception(f"VM crash:\n\n{out}")
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@tlively tlively Apr 27, 2026

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Why is this different than in other fuzz handlers?

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@kripken kripken Apr 27, 2026

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Our normal JS is very careful to swallow and log any JS errors. The return code of the process is always 0.

Here we are running JS that is itself a fuzz testcase, and might error.


# Clean up stack traces.
cleaned = []
for line in out.splitlines():
if 'RuntimeError:' in line or 'TypeError:' in line:
Expand All @@ -2240,7 +2245,14 @@ def do_run(self, vm, js, wasm):
# Ignore it, as details of traces differ based on optimizations.
continue
cleaned.append(line)
return '\n'.join(cleaned)
cleaned = '\n'.join(cleaned)

# Clean up function references, which can differ after opts, things like
#
# function 77() { [native code] }
#
cleaned = re.sub(r'function \d+\(\) ', 'function <ID>() ', cleaned)
return cleaned

def can_run_on_wasm(self, wasm):
return all_disallowed(DISALLOWED_FEATURES_IN_V8)
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