rust/src/atomic_shim.rs

//! Atomic intrinsics are implemented using a global lock for now, as Cranelift doesn't support
//! atomic operations yet.

// FIXME implement atomic instructions in Cranelift.

use crate::prelude::*;

#[cfg(feature = "jit")]
#[no_mangle]
pub static mut __cg_clif_global_atomic_mutex: libc::pthread_mutex_t =
    libc::PTHREAD_MUTEX_INITIALIZER;

pub(crate) fn init_global_lock(
    module: &mut impl Module,
    bcx: &mut FunctionBuilder<'_>,
    use_jit: bool,
) {
    if use_jit {
        // When using JIT, dylibs won't find the __cg_clif_global_atomic_mutex data object defined here,
        // so instead we define it in the cg_clif dylib.

        return;
    }

    let mut data_ctx = DataContext::new();
    data_ctx.define_zeroinit(1024); // 1024 bytes should be big enough on all platforms.
    data_ctx.set_align(16);
    let atomic_mutex = module
        .declare_data(
            "__cg_clif_global_atomic_mutex",
            Linkage::Export,
            true,
            false,
        )
        .unwrap();
    module.define_data(atomic_mutex, &data_ctx).unwrap();

    let pthread_mutex_init = module
        .declare_function(
            "pthread_mutex_init",
            Linkage::Import,
            &cranelift_codegen::ir::Signature {
                call_conv: module.target_config().default_call_conv,
                params: vec![
                    AbiParam::new(
                        module.target_config().pointer_type(), /* *mut pthread_mutex_t */
                    ),
                    AbiParam::new(
                        module.target_config().pointer_type(), /* *const pthread_mutex_attr_t */
                    ),
                ],
                returns: vec![AbiParam::new(types::I32 /* c_int */)],
            },
        )
        .unwrap();

    let pthread_mutex_init = module.declare_func_in_func(pthread_mutex_init, bcx.func);

    let atomic_mutex = module.declare_data_in_func(atomic_mutex, bcx.func);
    let atomic_mutex = bcx
        .ins()
        .global_value(module.target_config().pointer_type(), atomic_mutex);

    let nullptr = bcx.ins().iconst(module.target_config().pointer_type(), 0);

    bcx.ins().call(pthread_mutex_init, &[atomic_mutex, nullptr]);
}

pub(crate) fn init_global_lock_constructor(
    module: &mut impl Module,
    constructor_name: &str,
) -> FuncId {
    let sig = Signature::new(CallConv::SystemV);
    let init_func_id = module
        .declare_function(constructor_name, Linkage::Export, &sig)
        .unwrap();

    let mut ctx = Context::new();
    ctx.func = Function::with_name_signature(ExternalName::user(0, 0), sig);
    {
        let mut func_ctx = FunctionBuilderContext::new();
        let mut bcx = FunctionBuilder::new(&mut ctx.func, &mut func_ctx);

        let block = bcx.create_block();
        bcx.switch_to_block(block);

        crate::atomic_shim::init_global_lock(module, &mut bcx, false);

        bcx.ins().return_(&[]);
        bcx.seal_all_blocks();
        bcx.finalize();
    }
    module
        .define_function(
            init_func_id,
            &mut ctx,
            &mut cranelift_codegen::binemit::NullTrapSink {},
        )
        .unwrap();

    init_func_id
}

pub(crate) fn lock_global_lock(fx: &mut FunctionCx<'_, '_, impl Module>) {
    let atomic_mutex = fx
        .cx
        .module
        .declare_data(
            "__cg_clif_global_atomic_mutex",
            Linkage::Import,
            true,
            false,
        )
        .unwrap();

    let pthread_mutex_lock = fx
        .cx
        .module
        .declare_function(
            "pthread_mutex_lock",
            Linkage::Import,
            &cranelift_codegen::ir::Signature {
                call_conv: fx.cx.module.target_config().default_call_conv,
                params: vec![AbiParam::new(
                    fx.cx.module.target_config().pointer_type(), /* *mut pthread_mutex_t */
                )],
                returns: vec![AbiParam::new(types::I32 /* c_int */)],
            },
        )
        .unwrap();

    let pthread_mutex_lock = fx
        .cx
        .module
        .declare_func_in_func(pthread_mutex_lock, fx.bcx.func);

    let atomic_mutex = fx.cx.module.declare_data_in_func(atomic_mutex, fx.bcx.func);
    let atomic_mutex = fx
        .bcx
        .ins()
        .global_value(fx.cx.module.target_config().pointer_type(), atomic_mutex);

    fx.bcx.ins().call(pthread_mutex_lock, &[atomic_mutex]);
}

pub(crate) fn unlock_global_lock(fx: &mut FunctionCx<'_, '_, impl Module>) {
    let atomic_mutex = fx
        .cx
        .module
        .declare_data(
            "__cg_clif_global_atomic_mutex",
            Linkage::Import,
            true,
            false,
        )
        .unwrap();

    let pthread_mutex_unlock = fx
        .cx
        .module
        .declare_function(
            "pthread_mutex_unlock",
            Linkage::Import,
            &cranelift_codegen::ir::Signature {
                call_conv: fx.cx.module.target_config().default_call_conv,
                params: vec![AbiParam::new(
                    fx.cx.module.target_config().pointer_type(), /* *mut pthread_mutex_t */
                )],
                returns: vec![AbiParam::new(types::I32 /* c_int */)],
            },
        )
        .unwrap();

    let pthread_mutex_unlock = fx
        .cx
        .module
        .declare_func_in_func(pthread_mutex_unlock, fx.bcx.func);

    let atomic_mutex = fx.cx.module.declare_data_in_func(atomic_mutex, fx.bcx.func);
    let atomic_mutex = fx
        .bcx
        .ins()
        .global_value(fx.cx.module.target_config().pointer_type(), atomic_mutex);

    fx.bcx.ins().call(pthread_mutex_unlock, &[atomic_mutex]);
}