Make iprof a transparent stdio wrapper#513
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iprof ran the user binary via IO.popen, which connects the child's stdout to a pipe. The child's libc then sees a non-tty and switches to full block-buffering, so its output only appeared once it exited (e.g. all of `iprof -m full ./a.out` arrived in one block instead of streaming). Let the child inherit iprof's own stdout/stderr directly instead, so it sees exactly the descriptors iprof was given and picks the same buffering it would without iprof: line-buffered (streaming) on a terminal, block-buffered on a pipe/file. This also keeps stdout and stderr on their own streams. Add an integration test driving iprof under a PTY (via `script`) to check streaming with a real libc-buffered binary, and one checking stdout/stderr stay separate. The previous test used `bash echo`, which is not libc-buffered and so never exercised the bug. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Superb fix. |
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iprof ran the user binary via IO.popen, which connects the child's stdout to a pipe. The child's libc then sees a non-tty and switches to full block-buffering, so its output only appeared once it exited (e.g. all of
iprof -m full ./a.outarrived in one block instead of streaming).Let the child inherit iprof's own stdout/stderr directly instead, so it sees exactly the descriptors iprof was given and picks the same buffering it would without iprof: line-buffered (streaming) on a terminal, block-buffered on a pipe/file. This also keeps stdout and stderr on their own streams.
Add an integration test driving iprof under a PTY (via
script) to check streaming with a real libc-buffered binary, and one checking stdout/stderr stay separate. The previous test usedbash echo, which is not libc-buffered and so never exercised the bug.