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From: Alexey Izbyshev <>
Subject: [musl] [PATCH] poll: fix timespec kernel ABI mismatch on 32-bit arches without SYS_poll
Date: Thu,  2 Mar 2023 08:16:56 +0300	[thread overview]
Message-ID: <> (raw)

After migration to 64-bit time_t in struct timespec, passing it to
SYS_ppoll on arches where the syscall expects the 32-bit version of
the struct became wrong and results in overlaying 64-bit tv_sec over the
whole expected struct. In this case, tv_nsec is completely ignored, and
interpretation of tv_sec depends on endianness. Because its value in the
case of poll fits into 32 bits, on little endian arches tv_sec is
interpreted as the correct number of seconds and zero nanoseconds, so
the original timeout is effectively rounded down to seconds. On big
endian arches, tv_sec is interpreted as nanoseconds (and zero seconds),
so the original timeout is effectively divided by 10^9 and rounded down
to nanoseconds.

The only in-tree affected arch is or1k, which is big endian.

Fix this by passing the timeout in the array of the type actually
expected by the kernel for SYS_ppoll, as done in other time64-related
 src/select/poll.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/select/poll.c b/src/select/poll.c
index c84c8a99..d1caefcc 100644
--- a/src/select/poll.c
+++ b/src/select/poll.c
@@ -8,8 +8,14 @@ int poll(struct pollfd *fds, nfds_t n, int timeout)
 #ifdef SYS_poll
 	return syscall_cp(SYS_poll, fds, n, timeout);
-	return syscall_cp(SYS_ppoll, fds, n, timeout>=0 ?
-		&((struct timespec){ .tv_sec = timeout/1000,
-		.tv_nsec = timeout%1000*1000000 }) : 0, 0, _NSIG/8);
+	time_t s = timeout>=0 ? timeout/1000 : 0;
+	long ns = timeout>=0 ? timeout%1000*1000000 : 0;
+#ifdef SYS_ppoll_time64
+	if (SYS_ppoll == SYS_ppoll_time64)
+		return syscall_cp(SYS_ppoll_time64, fds, n,
+			timeout>=0 ? ((long long[]){s, ns}) : 0, 0, _NSIG/8);
+	return syscall_cp(SYS_ppoll, fds, n,
+		timeout>=0 ? ((long[]){s, ns}) : 0, 0, _NSIG/8);

             reply	other threads:[~2023-03-02  5:17 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-02  5:16 Alexey Izbyshev [this message]
2023-03-03  1:19 ` Rich Felker
2023-03-03  4:03   ` Alexey Izbyshev

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