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5e9d90b615
Avoid embedding the parent's sys.argv into the forkserver -c command
string via repr(). When sys.argv is large (e.g. thousands of file
paths from a pre-commit hook), the resulting single argument could
exceed the OS per-argument length limit (MAX_ARG_STRLEN on Linux,
typically 128 KiB), causing posix_spawn to fail and the parent to
observe a BrokenPipeError.
Instead, append the argv entries as separate command-line arguments
after -c; the forkserver child reads them back as sys.argv[1:]. This
cannot exceed any limit the parent itself did not already satisfy.
Regression introduced by gh-143706 / 298d5440eb.
30 lines
1 KiB
Python
30 lines
1 KiB
Python
# gh-144503: Test that the forkserver can start when the parent process has
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# a very large sys.argv. Prior to the fix, sys.argv was repr'd into the
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# forkserver ``-c`` command string which could exceed the OS limit on the
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# length of a single argv element (MAX_ARG_STRLEN on Linux, ~128 KiB),
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# causing posix_spawn to fail and the parent to see a BrokenPipeError.
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import multiprocessing
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import sys
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EXPECTED_LEN = 5002 # argv[0] + 5000 padding entries + sentinel
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def fun():
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print(f"worker:{len(sys.argv)}:{sys.argv[-1]}")
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if __name__ == "__main__":
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# Inflate sys.argv well past 128 KiB before the forkserver is started.
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sys.argv[1:] = ["x" * 50] * 5000 + ["sentinel"]
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assert len(sys.argv) == EXPECTED_LEN
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ctx = multiprocessing.get_context("forkserver")
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p = ctx.Process(target=fun)
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p.start()
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p.join()
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sys.exit(p.exitcode)
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else:
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# This branch runs when the forkserver preloads this module as
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# __mp_main__; confirm the large argv was propagated intact.
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print(f"preload:{len(sys.argv)}:{sys.argv[-1]}")
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