posix_spawn: Don't attempt to dup2 identical fds #214
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macOS Big Sur does not allow the user to `posix_spawn_file_actions_adddup2` an fd to itself. Instead of behaving as a no-op as specified by POSIX 2017.1 (and done by every other operating system), it instead fails with `EBADFD` in `posix_spawn`. This caused a single tricky-to-identify failure in GHC's testsuite.
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snoyberg
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| return -1; | ||
| } | ||
| // N.B. POSIX specifies that dup2(x,x) should be a no-op, but | ||
| // naturally Apple ignores this and rather fails in posix_spawn on Big |
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You have all my sympathies @bgamari
snoyberg
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Jul 28, 2021
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Editorial note: @snoyberg, I'd like to again apologize for how many iterations this
posix_spawnwork has required; it really has been a compatibility nightmare. This particular issue remained under the radar in my Darwin testing on GHC as I had chalked it up to a GHC bug, having seen the same test fail for reasons unrelated toprocess. Sadly, this time the failure is actually due to a bug in Darwin'sposix_spawn_file_actions_adddup2implementation. Thanks again, for your patience.macOS Big Sur does not allow the user to
posix_spawn_file_actions_adddup2anfd to itself. Instead of behaving as a no-op as specified by POSIX
2017.1 (and as done by every other operating system), it instead fails with
EBADFDinposix_spawn. This caused a single tricky-to-identifyfailure in GHC's testsuite.