Implement accept4 - #2779
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accept4 is wired to syscall_stub, so it returns ENOSYS. Go's net package uses it for every accepted connection, which is what ish-app#1889 and ish-app#2553 both report: "accept tcp [::]:9999: accept4: function not implemented". It is accept plus two flags that apply to the accepted fd: SOCK_CLOEXEC sets FD_CLOEXEC on it and SOCK_NONBLOCK sets O_NONBLOCK on it, neither touching the listener. Any other flag is EINVAL. The socketcall entry is filled in to match. Verified against real Linux with the same static i386 binary, over a loopback TCP connection: before after / real Linux accept4(flags=0) ENOSYS connected fd SOCK_CLOEXEC sets FD_CLOEXEC ENOSYS set listener FD_CLOEXEC untouched ok ok SOCK_NONBLOCK sets O_NONBLOCK ENOSYS set nonblocking accepted fd reads ENOSYS EAGAIN peer address filled in ENOSYS AF_INET bogus flags ENOSYS EINVAL
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accept4is wired tosyscall_stub, so it returns ENOSYS.Go's net package uses it for every accepted connection, which is what #1889 and #2553 both report:
Go has no fallback to plain
accept, so a Go server fails on its first connection.What it does
acceptplus two flags that apply to the accepted fd:SOCK_CLOEXECsetsFD_CLOEXECon it andSOCK_NONBLOCKsetsO_NONBLOCKon it, neither touching the listener. Any other flag is EINVAL. The socketcall entry is filled in to match.Verification
Same static i386 binary run on real Linux and on iSH, over a loopback TCP connection:
accept4(flags=0)SOCK_CLOEXECsetsFD_CLOEXECFD_CLOEXECuntouchedSOCK_NONBLOCKsetsO_NONBLOCKReproduced on the Alpine 3.19.0 rootfs the App Store build downloads (
ROOTFS_URLinapp/iSH.xcconfig), against master 7864dd6.python3from the mirrored 3.19 repo also reaches this path: CPython callsaccept4(SOCK_CLOEXEC)on Linux, and the log showsstub syscall 364on each accept. CPython does fall back to plainaccept()on ENOSYS, so it keeps working; the difference from Go is the fallback, not the call.