1 use crate::thread::Time;
3 use rustc_target::abi::{Align, Size};
4 use std::time::{Instant, SystemTime};
6 /// Implementation of the SYS_futex syscall.
8 this: &mut MiriEvalContext<'_, 'tcx>,
9 args: &[OpTy<'tcx, Tag>],
10 dest: &PlaceTy<'tcx, Tag>,
11 ) -> InterpResult<'tcx> {
12 // The amount of arguments used depends on the type of futex operation.
13 // The full futex syscall takes six arguments (excluding the syscall
14 // number), which is also the maximum amount of arguments a linux syscall
15 // can take on most architectures.
16 // However, not all futex operations use all six arguments. The unused ones
17 // may or may not be left out from the `syscall()` call.
18 // Therefore we don't use `check_arg_count` here, but only check for the
19 // number of arguments to fall within a range.
22 "incorrect number of arguments for `futex` syscall: got {}, expected at least 4",
27 // The first three arguments (after the syscall number itself) are the same to all futex operations:
28 // (int *addr, int op, int val).
29 // We checked above that these definitely exist.
30 let addr = this.read_immediate(&args[1])?;
31 let op = this.read_scalar(&args[2])?.to_i32()?;
32 let val = this.read_scalar(&args[3])?.to_i32()?;
34 let thread = this.get_active_thread();
35 let addr_scalar = addr.to_scalar()?;
37 let futex_private = this.eval_libc_i32("FUTEX_PRIVATE_FLAG")?;
38 let futex_wait = this.eval_libc_i32("FUTEX_WAIT")?;
39 let futex_wait_bitset = this.eval_libc_i32("FUTEX_WAIT_BITSET")?;
40 let futex_wake = this.eval_libc_i32("FUTEX_WAKE")?;
41 let futex_wake_bitset = this.eval_libc_i32("FUTEX_WAKE_BITSET")?;
42 let futex_realtime = this.eval_libc_i32("FUTEX_CLOCK_REALTIME")?;
44 // FUTEX_PRIVATE enables an optimization that stops it from working across processes.
45 // Miri doesn't support that anyway, so we ignore that flag.
46 match op & !futex_private {
47 // FUTEX_WAIT: (int *addr, int op = FUTEX_WAIT, int val, const timespec *timeout)
48 // Blocks the thread if *addr still equals val. Wakes up when FUTEX_WAKE is called on the same address,
49 // or *timeout expires. `timeout == null` for an infinite timeout.
51 // FUTEX_WAIT_BITSET: (int *addr, int op = FUTEX_WAIT_BITSET, int val, const timespec *timeout, int *_ignored, unsigned int bitset)
52 // This is identical to FUTEX_WAIT, except:
53 // - The timeout is absolute rather than relative.
54 // - You can specify the bitset to selecting what WAKE operations to respond to.
55 op if op & !futex_realtime == futex_wait || op & !futex_realtime == futex_wait_bitset => {
56 let wait_bitset = op & !futex_realtime == futex_wait_bitset;
58 let bitset = if wait_bitset {
61 "incorrect number of arguments for `futex` syscall with `op=FUTEX_WAIT_BITSET`: got {}, expected 7",
65 this.read_scalar(&args[6])?.to_u32()?
69 "incorrect number of arguments for `futex` syscall with `op=FUTEX_WAIT`: got {}, expected at least 5",
77 let einval = this.eval_libc("EINVAL")?;
78 this.set_last_error(einval)?;
79 this.write_scalar(Scalar::from_machine_isize(-1, this), dest)?;
83 // `deref_operand` but not actually dereferencing the ptr yet (it might be NULL!).
84 let timeout = this.ref_to_mplace(&this.read_immediate(&args[4])?)?;
85 let timeout_time = if this.ptr_is_null(timeout.ptr)? {
88 this.check_no_isolation(
89 "`futex` syscall with `op=FUTEX_WAIT` and non-null timeout",
91 let duration = match this.read_timespec(&timeout)? {
92 Some(duration) => duration,
94 let einval = this.eval_libc("EINVAL")?;
95 this.set_last_error(einval)?;
96 this.write_scalar(Scalar::from_machine_isize(-1, this), dest)?;
100 Some(if wait_bitset {
101 // FUTEX_WAIT_BITSET uses an absolute timestamp.
102 if op & futex_realtime != 0 {
103 Time::RealTime(SystemTime::UNIX_EPOCH.checked_add(duration).unwrap())
105 Time::Monotonic(this.machine.time_anchor.checked_add(duration).unwrap())
108 // FUTEX_WAIT uses a relative timestamp.
109 if op & futex_realtime != 0 {
110 Time::RealTime(SystemTime::now().checked_add(duration).unwrap())
112 Time::Monotonic(Instant::now().checked_add(duration).unwrap())
116 // Check the pointer for alignment and validity.
117 // The API requires `addr` to be a 4-byte aligned pointer, and will
118 // use the 4 bytes at the given address as an (atomic) i32.
119 this.check_ptr_access_align(
120 this.scalar_to_ptr(addr_scalar),
122 Align::from_bytes(4).unwrap(),
123 CheckInAllocMsg::MemoryAccessTest,
125 // Read an `i32` through the pointer, regardless of any wrapper types.
126 // It's not uncommon for `addr` to be passed as another type than `*mut i32`, such as `*const AtomicI32`.
127 // FIXME: this fails if `addr` is not a pointer type.
128 // The atomic ordering for futex(https://man7.org/linux/man-pages/man2/futex.2.html):
129 // "The load of the value of the futex word is an
130 // atomic memory access (i.e., using atomic machine instructions
131 // of the respective architecture). This load, the comparison
132 // with the expected value, and starting to sleep are performed
133 // atomically and totally ordered with respect to other futex
134 // operations on the same futex word."
135 // SeqCst is total order over all operations.
136 // FIXME: check if this should be changed when weak memory orders are added.
138 .read_scalar_at_offset_atomic(
141 this.machine.layouts.i32,
142 AtomicReadOp::SeqCst,
145 if val == futex_val {
146 // The value still matches, so we block the trait make it wait for FUTEX_WAKE.
147 this.block_thread(thread);
148 this.futex_wait(addr_scalar.to_machine_usize(this)?, thread, bitset);
149 // Succesfully waking up from FUTEX_WAIT always returns zero.
150 this.write_scalar(Scalar::from_machine_isize(0, this), dest)?;
151 // Register a timeout callback if a timeout was specified.
152 // This callback will override the return value when the timeout triggers.
154 if let Some(timeout_time) = timeout_time {
155 this.register_timeout_callback(
158 Box::new(move |this| {
159 this.unblock_thread(thread);
160 this.futex_remove_waiter(addr_scalar.to_machine_usize(this)?, thread);
161 let etimedout = this.eval_libc("ETIMEDOUT")?;
162 this.set_last_error(etimedout)?;
163 this.write_scalar(Scalar::from_machine_isize(-1, this), &dest)?;
169 // The futex value doesn't match the expected value, so we return failure
170 // right away without sleeping: -1 and errno set to EAGAIN.
171 let eagain = this.eval_libc("EAGAIN")?;
172 this.set_last_error(eagain)?;
173 this.write_scalar(Scalar::from_machine_isize(-1, this), dest)?;
176 // FUTEX_WAKE: (int *addr, int op = FUTEX_WAKE, int val)
177 // Wakes at most `val` threads waiting on the futex at `addr`.
178 // Returns the amount of threads woken up.
179 // Does not access the futex value at *addr.
180 // FUTEX_WAKE_BITSET: (int *addr, int op = FUTEX_WAKE, int val, const timespect *_unused, int *_unused, unsigned int bitset)
181 // Same as FUTEX_WAKE, but allows you to specify a bitset to select which threads to wake up.
182 op if op == futex_wake || op == futex_wake_bitset => {
183 let bitset = if op == futex_wake_bitset {
186 "incorrect number of arguments for `futex` syscall with `op=FUTEX_WAKE_BITSET`: got {}, expected 7",
190 this.read_scalar(&args[6])?.to_u32()?
195 let einval = this.eval_libc("EINVAL")?;
196 this.set_last_error(einval)?;
197 this.write_scalar(Scalar::from_machine_isize(-1, this), dest)?;
202 if let Some(thread) = this.futex_wake(addr_scalar.to_machine_usize(this)?, bitset) {
203 this.unblock_thread(thread);
204 this.unregister_timeout_callback_if_exists(thread);
210 this.write_scalar(Scalar::from_machine_isize(n, this), dest)?;
212 op => throw_unsup_format!("Miri does not support `futex` syscall with op={}", op),