samp_sdk/omp/

vtable.rs

//! Helpers for accessing vtables (primary and secondary) of server-owned C++ objects.
//!
//! In C++ with multiple inheritance, each base class with virtuals results in a
//! distinct vtable. The primary lies at offset 0 of the object; secondaries at
//! offsets that depend on the `sizeof` of the preceding bases. The offsets are
//! fixed per class and known at compile time (after layout analysis via disasm).
//!
//! This module centralizes the repeated pattern of:
//!
//! 1. Adjust the object pointer to point to a subobject (`obj + offset`).
//! 2. Read the secondary vtable (`*subobject`).
//! 3. Load the slot N pointer (`*(vtable + N * sizeof(usize))`).
//!
//! Each specific caller still performs the final `transmute` to the correct
//! function type, because the calling convention varies (`extern "C"`,
//! `extern "thiscall"`, variadic vs fixed arity).
//!
//! Slots are read and returned as `*const ()`, never as `usize`: a function
//! pointer rebuilt from an integer carries no provenance, and calling it is
//! undefined behavior under Rust's memory model.
//!
//! ## Example usage
//!
//! ```rust,no_run
//! # use samp_sdk::omp::vtable;
//! # use std::os::raw::{c_char, c_int};
//! # type LogLnFn = unsafe extern "C" fn(*mut u8, c_int, *const c_char, *const c_char);
//! # fn example(core: *mut u8, level: c_int, fmt: *const c_char, arg: *const c_char) -> Option<()> {
//! // ILogger at offset 56 inside ICore; logLn at slot [2].
//! let (this, f_ptr) = unsafe {
//!     vtable::secondary_call_target_ptr(core, 56, 2)?
//! };
//! let f: LogLnFn = unsafe { std::mem::transmute(f_ptr) };
//! unsafe { f(this, level, fmt, arg) };
//! # Some(()) }
//! ```

/// Returns the subobject pointer at `offset` bytes from `obj`.
///
/// For the primary base class (at offset 0), `offset = 0`. For secondary bases,
/// the offset is determined by the `sizeof` of the preceding bases in C++.
///
/// Returns `None` if `obj` is null.
///
/// # Safety
/// `obj` must be a valid pointer (or null). `offset` must be the correct offset
/// of the subobject — passing the wrong offset produces an invalid pointer.
#[inline]
pub unsafe fn subobject_ptr(obj: *mut u8, offset: isize) -> Option<*mut u8> {
    if obj.is_null() {
        return None;
    }
    Some(unsafe { obj.offset(offset) })
}

/// Reads the slot `slot` pointer from the vtable pointed to by `subobject`.
///
/// Returns `None` if `subobject` is null, the vtable is null, or the slot
/// contains zero (defensive against uninitialized or corrupted vtables).
///
/// # Safety
/// `subobject` must point to a valid C++ object whose first member is the vptr.
/// `slot` must be within the valid range of the vtable — reading a non-existent
/// slot yields an undefined value (but not aliasing UB).
#[deprecated(
    since = "3.5.0",
    note = "returns the address without provenance; use `vtable_slot_ptr`"
)]
#[inline]
pub unsafe fn vtable_slot(subobject: *mut u8, slot: usize) -> Option<usize> {
    unsafe { vtable_slot_ptr(subobject, slot) }.map(|f| f.addr())
}

/// Reads the slot `slot` function pointer from the vtable pointed to by `subobject`.
///
/// Returns `None` if `subobject` is null, the vtable is null, or the slot
/// is null (defensive against uninitialized or corrupted vtables). The pointer
/// keeps its provenance, so the caller may `transmute` it to a function type.
///
/// # Safety
/// `subobject` must point to a valid C++ object whose first member is the vptr.
/// `slot` must be within the valid range of the vtable.
#[inline]
pub unsafe fn vtable_slot_ptr(subobject: *mut u8, slot: usize) -> Option<*const ()> {
    if subobject.is_null() {
        return None;
    }
    // FFI: the first field of any C++ object with a virtual method is the
    // vtable pointer, always pointer-aligned by the ABI (Itanium and MSVC).
    #[allow(clippy::cast_ptr_alignment)]
    let vtable = unsafe { *(subobject as *const *const *const ()) };
    if vtable.is_null() {
        return None;
    }
    let f_ptr = unsafe { *vtable.add(slot) };
    if f_ptr.is_null() {
        return None;
    }
    Some(f_ptr)
}

/// Combines [`subobject_ptr`] + [`vtable_slot_ptr`] in a single helper.
///
/// Returns `(this, f_ptr)`: the `this` adjusted for the subobject (the first
/// arg of virtual method calls on that subobject) and the function pointer at
/// the slot. The caller does the `transmute` to the correct function type and
/// invokes it.
///
/// Returns `None` on any failure (`obj` null, vtable null, slot null).
///
/// # Safety
/// See [`subobject_ptr`] and [`vtable_slot_ptr`].
#[inline]
pub unsafe fn secondary_call_target_ptr(
    obj: *mut u8,
    offset: isize,
    slot: usize,
) -> Option<(*mut u8, *const ())> {
    let this = unsafe { subobject_ptr(obj, offset)? };
    let f_ptr = unsafe { vtable_slot_ptr(this, slot)? };
    Some((this, f_ptr))
}

/// Combines [`subobject_ptr`] + [`vtable_slot`] in a single helper.
///
/// Returns `(this, f_ptr)`: the `this` adjusted for the subobject (the first
/// arg of virtual method calls on that subobject) and the function pointer at
/// the slot. The caller does the `transmute` to the correct function type and
/// invokes it.
///
/// Returns `None` on any failure (`obj` null, vtable null, slot zero).
///
/// # Safety
/// See [`subobject_ptr`] and [`vtable_slot`].
#[deprecated(
    since = "3.5.0",
    note = "returns the address without provenance; use `secondary_call_target_ptr`"
)]
#[inline]
pub unsafe fn secondary_call_target(
    obj: *mut u8,
    offset: isize,
    slot: usize,
) -> Option<(*mut u8, usize)> {
    unsafe { secondary_call_target_ptr(obj, offset, slot) }.map(|(this, f)| (this, f.addr()))
}

/// Calls a virtual method through a server object's vtable.
///
/// Every wrapper in this module family repeats the same four steps: name the
/// function type for the target's calling convention, adjust `this` to the
/// right subobject, read the slot, and give up gracefully when either pointer
/// is missing. The macro is that sequence written once.
///
/// ```ignore
/// // bool IPlayer::isBot() const, slot 8, primary vtable
/// call_vtable!(player.cast::<u8>(), 0, SLOT_IS_BOT, () -> bool, (), false)
///
/// // void IPlayer::setHealth(float)
/// call_vtable!(player.cast::<u8>(), 0, SLOT_SET_HEALTH, (f32) -> (), (health), ())
/// ```
///
/// The last argument is what to return when the object, its vtable or the slot
/// is null — the "fails closed" behaviour the null-safety tests check. Methods
/// whose return type crosses the ABI differently (a struct through a hidden
/// pointer, say) are written out by hand instead.
macro_rules! call_vtable {
    (
        $ptr:expr, $offset:expr, $slot:expr,
        ($($arg_ty:ty),* $(,)?) -> $ret:ty,
        ($($arg:expr),* $(,)?),
        $absent:expr
    ) => {{
        #[cfg(not(target_env = "msvc"))]
        type VirtualFn = unsafe extern "C" fn(*mut u8 $(, $arg_ty)*) -> $ret;
        #[cfg(target_env = "msvc")]
        type VirtualFn = unsafe extern "thiscall" fn(*mut u8 $(, $arg_ty)*) -> $ret;

        match unsafe { $crate::omp::vtable::secondary_call_target_ptr($ptr, $offset, $slot) } {
            Some((this, f_ptr)) => {
                let call: VirtualFn = unsafe { std::mem::transmute(f_ptr) };
                unsafe { call(this $(, $arg)*) }
            }
            None => $absent,
        }
    }};
}

pub(crate) use call_vtable;

/// Function-pointer table for unit-test mocks. Raw pointers are not `Sync`,
/// so the wrapper lets a mock vtable live in a `static`.
#[cfg(test)]
pub(crate) struct MockTable<const N: usize>(pub [*const (); N]);

// SAFETY: the table is written once at init and only read afterwards.
#[cfg(test)]
unsafe impl<const N: usize> Sync for MockTable<N> {}
#[cfg(test)]
unsafe impl<const N: usize> Send for MockTable<N> {}

#[cfg(test)]
mod tests {
    use super::*;

    const DUMMY: [u8; 8] = [0; 8];

    /// Fake function pointers into `DUMMY`: never called, only compared.
    fn fake(i: usize) -> *const () {
        DUMMY.as_ptr().wrapping_add(i).cast()
    }

    /// Creates a 32-pointer buffer; at `byte_offset` it installs the vptr for `table`.
    fn make_obj_with_secondary_vtable(byte_offset: isize, table: &[*const ()]) -> [*const (); 32] {
        let mut buf = [std::ptr::null::<()>(); 32];
        let idx = usize::try_from(byte_offset).expect("byte_offset must be >= 0")
            / std::mem::size_of::<*const ()>();
        buf[idx] = table.as_ptr().cast();
        buf
    }

    #[test]
    fn subobject_ptr_returns_none_for_null() {
        assert!(unsafe { subobject_ptr(std::ptr::null_mut(), 56) }.is_none());
    }

    #[test]
    fn subobject_ptr_adds_offset_correctly() {
        let mut buf = [0u8; 64];
        let base = buf.as_mut_ptr();
        let sub = unsafe { subobject_ptr(base, 56) }.unwrap();
        assert_eq!(sub, base.wrapping_add(56));
    }

    #[test]
    fn vtable_slot_ptr_returns_none_for_null_subobject() {
        assert!(unsafe { vtable_slot_ptr(std::ptr::null_mut(), 0) }.is_none());
    }

    #[test]
    fn vtable_slot_ptr_null_slot_returns_none() {
        let table = [fake(0), fake(1), std::ptr::null()];
        let mut buf = make_obj_with_secondary_vtable(0, &table);
        let buf_u8 = buf.as_mut_ptr().cast::<u8>();
        assert!(unsafe { vtable_slot_ptr(buf_u8, 2) }.is_none());
        assert_eq!(unsafe { vtable_slot_ptr(buf_u8, 0) }, Some(fake(0)));
    }

    #[test]
    fn secondary_call_target_ptr_combines_both() {
        let table: Vec<*const ()> = (0..8).map(fake).collect();
        let mut buf = make_obj_with_secondary_vtable(56, &table);
        let buf_u8 = buf.as_mut_ptr().cast::<u8>();
        let (this, f_ptr) = unsafe { secondary_call_target_ptr(buf_u8, 56, 3).unwrap() };
        assert_eq!(this, buf_u8.wrapping_add(56));
        assert_eq!(f_ptr, fake(3));
    }

    #[test]
    fn secondary_call_target_ptr_null_obj_returns_none() {
        assert!(unsafe { secondary_call_target_ptr(std::ptr::null_mut(), 56, 0) }.is_none());
    }

    #[test]
    fn secondary_call_target_ptr_null_slot_returns_none() {
        let table = [std::ptr::null::<()>()];
        let mut buf = make_obj_with_secondary_vtable(8, &table);
        let buf_u8 = buf.as_mut_ptr().cast::<u8>();
        assert!(unsafe { secondary_call_target_ptr(buf_u8, 8, 0) }.is_none());
    }

    #[test]
    #[allow(deprecated)]
    fn deprecated_wrappers_return_the_same_address() {
        let table: Vec<*const ()> = (0..8).map(fake).collect();
        let mut buf = make_obj_with_secondary_vtable(56, &table);
        let buf_u8 = buf.as_mut_ptr().cast::<u8>();
        let (_, f) = unsafe { secondary_call_target(buf_u8, 56, 3).unwrap() };
        assert_eq!(f, fake(3).addr());
        let sub = buf_u8.wrapping_add(56);
        assert_eq!(unsafe { vtable_slot(sub, 5) }, Some(fake(5).addr()));
    }
}