bjoernager/rust
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support passing unsized fn arguments

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This commit is contained in:
Ralf Jung 2022-07-02 17:09:40 -04:00
parent 8ef0caa23c
commit 47cb276ab8
2 changed files with 54 additions and 12 deletions
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36
compiler/rustc_const_eval/src/interpret/terminator.rs
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@ -12,8 +12,8 @@ use rustc_target::abi::call::{ArgAbi, ArgAttribute, ArgAttributes, FnAbi, PassMo
use rustc_target::spec::abi::Abi;
use super::{
FnVal, ImmTy, InterpCx, InterpResult, MPlaceTy, Machine, OpTy, PlaceTy, Scalar,
StackPopCleanup, StackPopUnwind,
FnVal, ImmTy, Immediate, InterpCx, InterpResult, MPlaceTy, Machine, MemoryKind, OpTy, Operand,
PlaceTy, Scalar, StackPopCleanup, StackPopUnwind,
};
impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
@ -185,11 +185,16 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
// No question
return true;
}
if caller_abi.layout.is_unsized() || callee_abi.layout.is_unsized() {
// No, no, no. We require the types to *exactly* match for unsized arguments. If
// these are somehow unsized "in a different way" (say, `dyn Trait` vs `[i32]`),
// then who knows what happens.
return false;
}
if caller_abi.layout.size != callee_abi.layout.size
|| caller_abi.layout.align.abi != callee_abi.layout.align.abi
{
// This cannot go well...
// FIXME: What about unsized types?
return false;
}
// The rest *should* be okay, but we are extra conservative.
@ -287,6 +292,31 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
caller_arg.layout.ty
)
}
// Special handling for unsized parameters.
if caller_arg.layout.is_unsized() {
// `check_argument_compat` ensures that both have the same type, so we know they will use the metadata the same way.
assert_eq!(caller_arg.layout.ty, callee_arg.layout.ty);
// We have to properly pre-allocate the memory for the callee.
// So let's tear down some wrappers.
// This all has to be in memory, there are no immediate unsized values.
let src = caller_arg.assert_mem_place();
// The destination cannot be one of these "spread args".
let (dest_frame, dest_local) = callee_arg.assert_local();
// We are just initializing things, so there can't be anything here yet.
assert!(matches!(
*self.local_to_op(&self.stack()[dest_frame], dest_local, None)?,
Operand::Immediate(Immediate::Uninit)
));
// Allocate enough memory to hold `src`.
let Some((size, align)) = self.size_and_align_of_mplace(&src)? else {
span_bug!(self.cur_span(), "unsized fn arg with `extern` type tail should not be allowed")
};
let ptr = self.allocate_ptr(size, align, MemoryKind::Stack)?;
let dest_place =
MPlaceTy::from_aligned_ptr_with_meta(ptr.into(), callee_arg.layout, src.meta);
// Update the local to be that new place.
*M::access_local_mut(self, dest_frame, dest_local)? = Operand::Indirect(*dest_place);
}
// We allow some transmutes here.
// FIXME: Depending on the PassMode, this should reset some padding to uninitialized. (This
// is true for all `copy_op`, but there are a lot of special cases for argument passing