components/nacl/loader/nonsfi/irt_futex.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include <errno.h>
   6 #include <linux/futex.h>
   7 #include <sys/syscall.h>
   8 #include <sys/time.h>
   9 #include <unistd.h>
  10
  11 #include "components/nacl/loader/nonsfi/irt_interfaces.h"
  12 #include "components/nacl/loader/nonsfi/irt_util.h"
  13 #include "native_client/src/trusted/service_runtime/include/sys/time.h"
  14
  15 namespace nacl {
  16 namespace nonsfi {
  17 namespace {
  18
  19 // Converts a pair of NaCl's timespec of absolute time and host's timespec of
  20 // the current time to host's timespec of the relative time between them.
  21 // Note that assuming tv_nsec for the both input structs are non-negative,
  22 // the returned reltime's tv_nsec is also always non-negative.
  23 // (I.e., for -0.1 sec, {tv_sec: -1, tv_nsec: 900000000} will be returned).
  24 void NaClAbsTimeToRelTime(const struct nacl_abi_timespec& nacl_abstime,
  25                           const struct timespec& now,
  26                           struct timespec* reltime) {
  27   reltime->tv_sec = nacl_abstime.tv_sec - now.tv_sec;
  28   reltime->tv_nsec = nacl_abstime.tv_nsec - now.tv_nsec;
  29   if (reltime->tv_nsec < 0) {
  30     reltime->tv_sec -= 1;
  31     reltime->tv_nsec += 1000000000;
  32   }
  33 }
  34
  35 int IrtFutexWaitAbs(volatile int* addr, int value,
  36                     const struct nacl_abi_timespec* abstime) {
  37   struct timespec timeout;
  38   struct timespec* timeout_ptr = NULL;
  39   if (abstime) {
  40     // futex syscall takes relative timeout, but the ABI for IRT's
  41     // futex_wait_abs is absolute timeout. So, here we convert it.
  42     struct timespec now;
  43     if (clock_gettime(CLOCK_REALTIME, &now))
  44       return errno;
  45     NaClAbsTimeToRelTime(*abstime, now, &timeout);
  46
  47     // Linux's FUTEX_WAIT returns EINVAL for negative timeout, but an absolute
  48     // time that is in the past is a valid argument to irt_futex_wait_abs(),
  49     // and a caller expects ETIMEDOUT.
  50     // Here check only tv_sec since we assume time_t is signed. See also
  51     // the comment for NaClAbsTimeToRelTime.
  52     if (timeout.tv_sec < 0)
  53       return ETIMEDOUT;
  54     timeout_ptr = &timeout;
  55   }
  56   return CheckError(
  57       syscall(SYS_futex, addr, FUTEX_WAIT_PRIVATE, value, timeout_ptr, 0, 0));
  58 }
  59
  60 int IrtFutexWake(volatile int* addr, int nwake, int* count) {
  61   return CheckErrorWithResult(
  62       syscall(SYS_futex, addr, FUTEX_WAKE_PRIVATE, nwake, 0, 0, 0), count);
  63 }
  64
  65 }  // namespace
  66
  67 // For futex_wait_abs, the argument type should be nacl_abi_timespec. However,
  68 // the definition uses its host type, struct timespec. So, here we need to cast
  69 // it.
  70 const nacl_irt_futex kIrtFutex = {
  71   reinterpret_cast<int(*)(volatile int*, int, const struct timespec*)>(
  72       IrtFutexWaitAbs),
  73   IrtFutexWake,
  74 };
  75
  76 }  // namespace nonsfi
  77 }  // namespace nacl