rust/src/trap.rs

use std::collections::hash_map::DefaultHasher;
use std::hash::{Hash, Hasher};

use crate::prelude::*;

fn codegen_print(fx: &mut FunctionCx<'_, '_, impl cranelift_module::Backend>, msg: &str) {
    let puts = fx
        .module
        .declare_function(
            "puts",
            Linkage::Import,
            &Signature {
                call_conv: CallConv::triple_default(fx.triple()),
                params: vec![AbiParam::new(pointer_ty(fx.tcx))],
                returns: vec![],
            },
        )
        .unwrap();
    let puts = fx.module.declare_func_in_func(puts, &mut fx.bcx.func);
    #[cfg(debug_assertions)]
    {
        fx.add_comment(puts, "puts");
    }

    let symbol_name = fx.tcx.symbol_name(fx.instance);
    let real_msg = format!("trap at {:?} ({}): {}\0", fx.instance, symbol_name, msg);
    let mut hasher = DefaultHasher::new();
    real_msg.hash(&mut hasher);
    let msg_hash = hasher.finish();
    let mut data_ctx = DataContext::new();
    data_ctx.define(real_msg.as_bytes().to_vec().into_boxed_slice());
    let msg_id = fx
        .module
        .declare_data(
            &format!("__trap_{:08x}", msg_hash),
            Linkage::Local,
            false,
            false,
            None,
        )
        .unwrap();

    // Ignore DuplicateDefinition error, as the data will be the same
    let _ = fx.module.define_data(msg_id, &data_ctx);

    let local_msg_id = fx.module.declare_data_in_func(msg_id, fx.bcx.func);
    #[cfg(debug_assertions)]
    {
        fx.add_comment(local_msg_id, msg);
    }
    let msg_ptr = fx.bcx.ins().global_value(pointer_ty(fx.tcx), local_msg_id);
    fx.bcx.ins().call(puts, &[msg_ptr]);
}

/// Use this when `rustc_codegen_llvm` would insert a call to the panic handler.
///
/// Trap code: user0
pub(crate) fn trap_panic(
    fx: &mut FunctionCx<'_, '_, impl cranelift_module::Backend>,
    msg: impl AsRef<str>,
) {
    codegen_print(fx, msg.as_ref());
    fx.bcx.ins().trap(TrapCode::User(0));
}

/// Use this for example when a function call should never return. This will fill the current block,
/// so you can **not** add instructions to it afterwards.
///
/// Trap code: user65535
pub(crate) fn trap_unreachable(
    fx: &mut FunctionCx<'_, '_, impl cranelift_module::Backend>,
    msg: impl AsRef<str>,
) {
    codegen_print(fx, msg.as_ref());
    fx.bcx.ins().trap(TrapCode::UnreachableCodeReached);
}

/// Like `trap_unreachable` but returns a fake value of the specified type.
///
/// Trap code: user65535
pub(crate) fn trap_unreachable_ret_value<'tcx>(
    fx: &mut FunctionCx<'_, 'tcx, impl cranelift_module::Backend>,
    dest_layout: TyLayout<'tcx>,
    msg: impl AsRef<str>,
) -> CValue<'tcx> {
    trap_unreachable(fx, msg);
    CValue::by_ref(Pointer::const_addr(fx, 0), dest_layout)
}

/// Use this when something is unimplemented, but `libcore` or `libstd` requires it to codegen.
/// Unlike `trap_unreachable` this will not fill the current block, so you **must** add instructions
/// to it afterwards.
///
/// Trap code: user65535
pub(crate) fn trap_unimplemented(
    fx: &mut FunctionCx<'_, '_, impl cranelift_module::Backend>,
    msg: impl AsRef<str>,
) {
    codegen_print(fx, msg.as_ref());
    let true_ = fx.bcx.ins().iconst(types::I32, 1);
    fx.bcx.ins().trapnz(true_, TrapCode::User(!0));
}

/// Like `trap_unimplemented` but returns a fake value of the specified type.
///
/// Trap code: user65535
pub(crate) fn trap_unimplemented_ret_value<'tcx>(
    fx: &mut FunctionCx<'_, 'tcx, impl cranelift_module::Backend>,
    dest_layout: TyLayout<'tcx>,
    msg: impl AsRef<str>,
) -> CValue<'tcx> {
    trap_unimplemented(fx, msg);
    CValue::by_ref(Pointer::const_addr(fx, 0), dest_layout)
}