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simplify Linux futex impl a bit

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This commit is contained in:
Ralf Jung 2022-10-28 15:50:41 +02:00
parent 3f6fc1fb5a
commit 8f99d011f2
1 changed files with 7 additions and 22 deletions
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29
src/tools/miri/src/shims/unix/linux/sync.rs
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@ -1,7 +1,7 @@
use std::time::SystemTime;
use crate::concurrency::thread::{MachineCallback, Time};
use crate::*;
use rustc_target::abi::{Align, Size};
use std::time::SystemTime;
/// Implementation of the SYS_futex syscall.
/// `args` is the arguments *after* the syscall number.
@ -28,13 +28,14 @@ pub fn futex<'tcx>(
// The first three arguments (after the syscall number itself) are the same to all futex operations:
// (int *addr, int op, int val).
// We checked above that these definitely exist.
let addr = this.read_immediate(&args[0])?;
let addr = this.read_pointer(&args[0])?;
let op = this.read_scalar(&args[1])?.to_i32()?;
let val = this.read_scalar(&args[2])?.to_i32()?;
let thread = this.get_active_thread();
let addr_scalar = addr.to_scalar();
let addr_usize = addr_scalar.to_machine_usize(this)?;
// This is a vararg function so we have to bring our own type for this pointer.
let addr = MPlaceTy::from_aligned_ptr(addr, this.machine.layouts.i32);
let addr_usize = addr.ptr.addr().bytes();
let futex_private = this.eval_libc_i32("FUTEX_PRIVATE_FLAG")?;
let futex_wait = this.eval_libc_i32("FUTEX_WAIT")?;
@ -117,15 +118,6 @@ pub fn futex<'tcx>(
}
})
};
// Check the pointer for alignment and validity.
// The API requires `addr` to be a 4-byte aligned pointer, and will
// use the 4 bytes at the given address as an (atomic) i32.
this.check_ptr_access_align(
addr_scalar.to_pointer(this)?,
Size::from_bytes(4),
Align::from_bytes(4).unwrap(),
CheckInAllocMsg::MemoryAccessTest,
)?;
// There may be a concurrent thread changing the value of addr
// and then invoking the FUTEX_WAKE syscall. It is critical that the
// effects of this and the other thread are correctly observed,
@ -172,14 +164,7 @@ pub fn futex<'tcx>(
this.atomic_fence(AtomicFenceOrd::SeqCst)?;
// Read an `i32` through the pointer, regardless of any wrapper types.
// It's not uncommon for `addr` to be passed as another type than `*mut i32`, such as `*const AtomicI32`.
let futex_val = this
.read_scalar_at_offset_atomic(
&addr.into(),
0,
this.machine.layouts.i32,
AtomicReadOrd::Relaxed,
)?
.to_i32()?;
let futex_val = this.read_scalar_atomic(&addr, AtomicReadOrd::Relaxed)?.to_i32()?;
if val == futex_val {
// The value still matches, so we block the thread make it wait for FUTEX_WAKE.
this.block_thread(thread);