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authorRich Felker <dalias@aerifal.cx>2019-07-29 21:08:43 -0400
committerRich Felker <dalias@aerifal.cx>2019-07-30 14:23:56 -0400
commit722a1ae3351a03ab25010dbebd492eced664853b (patch)
tree746ede9edc9520201dfee63df68d9409a9295d5c /arch/x32
parent6a4a1691a0653bd51a30c2b8ac19448b7ebac796 (diff)
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select: overhaul for time64
major changes are made alongside adding time64 syscall support to
account for issues found during research. select historically accepts
non-normalized (tv_usec not restricted to less than 1000000) timeouts,
and the kernel normalizes them, but the normalization code is buggy
and subject to integer overflows. since normalization is needed anyway
when using SYS_pselect6 or SYS_pselect6_time64 as the backend, simply
do it up-front to eliminate both code path complexity and the
possibility of kernel bugs.

as a side effect, select no longer updates the caller's timeout
timeval with the remaining time. previously, archs that used
SYS_select updated it and archs that used SYS_pselect6 didn't. this
change may turn out to be controversial and may need revisiting, but
in any case the old behavior was not strictly conforming.

POSIX allows modification of the timeout "upon successful completion",
but the Linux syscall modifies it upon unsuccessful completion (EINTR)
as well (and presumably each time the syscall stops and restarts
before it's known whether completion will be successful). it's
possible that this language does not reflect the actual intent of the
standard, since other historical implementations probably behaved like
Linux, but that should be clarified if there's a desire to bring the
old behavior back. regardless, programs that are depending on this are
not correct and are already broken on some archs we support.
Diffstat (limited to 'arch/x32')
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