cb2d2ae56a
We need CLOCK_MONOTONIC equivalent implementation for z/OS within libc++. The default implementation is asserting. On z/OS the lack of 'clock_gettime()' and 'time_point()' force us to look for alternatives. The current proposal is to use `gettimeofday()` for CLOCK_MONOTONIC which is also used in CLOCK_REALTIME. This will allow us to skip the assertion with compromised CLOCK_MONOTONIC implementation which will not guarantee to never go back in time because it will use `gettimeofday()` but only when it's set. Is this a good compromise for platforms which does not support monotonic clock? Hopefully this will spark the discussion and agreement how to proceed in this situation. Reviewed By: #libc, ldionne, hubert.reinterpretcast Differential Revision: https://reviews.llvm.org/D93542
54 lines
1.6 KiB
C++
54 lines
1.6 KiB
C++
// -*- C++ -*-
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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP_SUPPORT_IBM_GETTOD_ZOS_H
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#define _LIBCPP_SUPPORT_IBM_GETTOD_ZOS_H
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#include <time.h>
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static inline int gettimeofdayMonotonic(struct timespec64* Output) {
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// The POSIX gettimeofday() function is not available on z/OS. Therefore,
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// we will call stcke and other hardware instructions in implement equivalent.
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// Note that nanoseconds alone will overflow when reaching new epoch in 2042.
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struct _t {
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uint64_t Hi;
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uint64_t Lo;
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};
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struct _t Value = {0, 0};
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uint64_t CC = 0;
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asm(" stcke %0\n"
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" ipm %1\n"
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" srlg %1,%1,28\n"
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: "=m"(Value), "+r"(CC)::);
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if (CC != 0) {
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errno = EMVSTODNOTSET;
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return CC;
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}
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uint64_t us = (Value.Hi >> 4);
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uint64_t ns = ((Value.Hi & 0x0F) << 8) + (Value.Lo >> 56);
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ns = (ns * 1000) >> 12;
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us = us - 2208988800000000;
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register uint64_t DivPair0 asm("r0"); // dividend (upper half), remainder
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DivPair0 = 0;
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register uint64_t DivPair1 asm("r1"); // dividend (lower half), quotient
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DivPair1 = us;
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uint64_t Divisor = 1000000;
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asm(" dlgr %0,%2" : "+r"(DivPair0), "+r"(DivPair1) : "r"(Divisor) :);
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Output->tv_sec = DivPair1;
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Output->tv_nsec = DivPair0 * 1000 + ns;
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return 0;
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}
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#endif // _LIBCPP_SUPPORT_IBM_GETTOD_ZOS_H
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