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FUTEX_WAKE_OP: use atomic read-modify-write memory access #2147

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FUTEX_WAKE_OP: use atomic read-modify-write memory access #2147

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732802d
FUTEX_WAKE_OP: return error if op is not supported
Mar 15, 2026
b285bb7
FUTEX_WAKE_OP: use atomic read-modify-write memory access
Mar 15, 2026
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19 changes: 10 additions & 9 deletions src/unix/futex.c
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Original file line number Diff line number Diff line change
Expand Up @@ -247,22 +247,23 @@ sysreturn futex(int *uaddr, int futex_op, int val,
struct futex *f2 = soft_create_futex(current->p, u64_from_pointer(uaddr2));
if (f2 == INVALID_ADDRESS)
return -ENOMEM;
boolean fault = false;
spin_lock_2(&f->lock, &f2->lock);
if (context_set_err(ctx)) {
fault = true;
ret = -EFAULT;
goto wake_op_done;
}
oldval = *(int *) uaddr2;

switch (op) {
case FUTEX_OP_SET: *uaddr2 = oparg; break;
case FUTEX_OP_ADD: *uaddr2 += oparg; break;
case FUTEX_OP_OR: *uaddr2 |= oparg; break;
case FUTEX_OP_ANDN: *uaddr2 &= ~oparg; break;
case FUTEX_OP_XOR: *uaddr2 ^= oparg; break;
case FUTEX_OP_SET: oldval = __atomic_exchange_n(uaddr2, oparg, __ATOMIC_RELAXED); break;
case FUTEX_OP_ADD: oldval = __atomic_fetch_add(uaddr2, oparg, __ATOMIC_RELAXED); break;
case FUTEX_OP_OR: oldval = __atomic_fetch_or(uaddr2, oparg, __ATOMIC_RELAXED); break;
case FUTEX_OP_ANDN: oldval = __atomic_fetch_and(uaddr2, ~oparg, __ATOMIC_RELAXED); break;
case FUTEX_OP_XOR: oldval = __atomic_fetch_xor(uaddr2, oparg, __ATOMIC_RELAXED); break;
default: ret = -ENOSYS; break;
}
context_clear_err(ctx);
if (ret)
goto wake_op_done;

wake1 = futex_wake_many(f, val);

Expand All @@ -284,7 +285,7 @@ sysreturn futex(int *uaddr, int futex_op, int val,
wake_op_done:
futex_unlock(f2);
futex_unlock(f);
return fault ? -EFAULT : wake1 + wake2;
return ret ? ret : wake1 + wake2;
}

case FUTEX_WAIT_BITSET: {
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