rust/src/vtable.rs

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//! See librustc_codegen_llvm/meth.rs for reference
use crate::prelude::*;
const DROP_FN_INDEX: usize = 0;
const SIZE_INDEX: usize = 1;
const ALIGN_INDEX: usize = 2;
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fn vtable_memflags() -> MemFlags {
let mut flags = MemFlags::trusted(); // A vtable access is always aligned and will never trap.
flags.set_readonly(); // A vtable is always read-only.
flags
}
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pub fn drop_fn_of_obj(fx: &mut FunctionCx<'_, '_, impl Backend>, vtable: Value) -> Value {
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let usize_size = fx.layout_of(fx.tcx.types.usize).size.bytes() as usize;
fx.bcx.ins().load(
pointer_ty(fx.tcx),
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vtable_memflags(),
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vtable,
(DROP_FN_INDEX * usize_size) as i32,
)
}
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pub fn size_of_obj(fx: &mut FunctionCx<'_, '_, impl Backend>, vtable: Value) -> Value {
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let usize_size = fx.layout_of(fx.tcx.types.usize).size.bytes() as usize;
fx.bcx.ins().load(
pointer_ty(fx.tcx),
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vtable_memflags(),
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vtable,
(SIZE_INDEX * usize_size) as i32,
)
}
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pub fn min_align_of_obj(fx: &mut FunctionCx<'_, '_, impl Backend>, vtable: Value) -> Value {
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let usize_size = fx.layout_of(fx.tcx.types.usize).size.bytes() as usize;
fx.bcx.ins().load(
pointer_ty(fx.tcx),
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vtable_memflags(),
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vtable,
(ALIGN_INDEX * usize_size) as i32,
)
}
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pub fn get_ptr_and_method_ref<'tcx>(
fx: &mut FunctionCx<'_, 'tcx, impl Backend>,
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arg: CValue<'tcx>,
idx: usize,
) -> (Value, Value) {
let (ptr, vtable) = arg.load_scalar_pair(fx);
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let usize_size = fx.layout_of(fx.tcx.types.usize).size.bytes();
let func_ref = fx.bcx.ins().load(
pointer_ty(fx.tcx),
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vtable_memflags(),
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vtable,
((idx + 3) * usize_size as usize) as i32,
);
(ptr, func_ref)
}
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pub fn get_vtable<'tcx>(
fx: &mut FunctionCx<'_, 'tcx, impl Backend>,
layout: TyLayout<'tcx>,
trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
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) -> Value {
let data_id = if let Some(data_id) = fx.vtables.get(&(layout.ty, trait_ref)) {
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*data_id
} else {
let data_id = build_vtable(fx, layout, trait_ref);
fx.vtables.insert((layout.ty, trait_ref), data_id);
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data_id
};
let local_data_id = fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
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fx.bcx.ins().global_value(fx.pointer_type, local_data_id)
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}
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fn build_vtable<'tcx>(
fx: &mut FunctionCx<'_, 'tcx, impl Backend>,
layout: TyLayout<'tcx>,
trait_ref: Option<ty::PolyExistentialTraitRef<'tcx>>,
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) -> DataId {
let tcx = fx.tcx;
let usize_size = fx.layout_of(fx.tcx.types.usize).size.bytes() as usize;
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let drop_in_place_fn =
import_function(tcx, fx.module, Instance::resolve_drop_in_place(tcx, layout.ty));
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let mut components: Vec<_> = vec![Some(drop_in_place_fn), None, None];
let methods_root;
let methods = if let Some(trait_ref) = trait_ref {
methods_root = tcx.vtable_methods(trait_ref.with_self_ty(tcx, layout.ty));
methods_root.iter()
} else {
(&[]).iter()
};
let methods = methods.cloned().map(|opt_mth| {
opt_mth.map_or(None, |(def_id, substs)| {
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Some(import_function(
tcx,
fx.module,
Instance::resolve_for_vtable(tcx, ParamEnv::reveal_all(), def_id, substs).unwrap(),
))
})
});
components.extend(methods);
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let mut data_ctx = DataContext::new();
let mut data = ::std::iter::repeat(0u8)
.take(components.len() * usize_size)
.collect::<Vec<u8>>()
.into_boxed_slice();
write_usize(fx.tcx, &mut data, SIZE_INDEX, layout.size.bytes());
write_usize(fx.tcx, &mut data, ALIGN_INDEX, layout.align.abi.bytes());
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data_ctx.define(data);
for (i, component) in components.into_iter().enumerate() {
if let Some(func_id) = component {
let func_ref = fx.module.declare_func_in_data(func_id, &mut data_ctx);
data_ctx.write_function_addr((i * usize_size) as u32, func_ref);
}
}
let data_id = fx
.module
.declare_data(
&format!("vtable.{:?}.for.{:?}", trait_ref, layout.ty),
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Linkage::Local,
false,
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false,
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Some(
fx.tcx
.data_layout
.pointer_align
.pref
.bytes()
.try_into()
.unwrap(),
),
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)
.unwrap();
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match fx.module.define_data(data_id, &data_ctx) {
Ok(()) | Err(cranelift_module::ModuleError::DuplicateDefinition(_)) => {}
err => err.unwrap(),
}
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data_id
}
fn write_usize(tcx: TyCtxt, buf: &mut [u8], idx: usize, num: u64) {
use byteorder::{BigEndian, LittleEndian, WriteBytesExt};
let usize_size = tcx
.layout_of(ParamEnv::reveal_all().and(tcx.types.usize))
.unwrap()
.size
.bytes() as usize;
let mut target = &mut buf[idx * usize_size..(idx + 1) * usize_size];
match tcx.data_layout.endian {
layout::Endian::Little => target.write_uint::<LittleEndian>(num, usize_size),
layout::Endian::Big => target.write_uint::<BigEndian>(num, usize_size),
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}
.unwrap()
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}