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Auto merge of #115182 - RalfJung:abi-compat-sign, r=b-naber

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miri ABI compatibility check: accept u32 and i32

If only the sign differs, then surely these types are compatible. (We do still check that `arg_ext` is the same, just in case.)

Also I made it so that the ABI check must *imply* that size and alignment are the same, but it doesn't actively check that itself. With how crazy ABI constraints get, having equal size and align really shouldn't be used as a signal for anything I think...
This commit is contained in:
bors 2023-08-28 22:56:10 +00:00
commit 191dc54dbf
2 changed files with 56 additions and 15 deletions
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44
compiler/rustc_const_eval/src/interpret/terminator.rs
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@ -255,6 +255,16 @@ fn check_argument_compat(
caller_abi: &ArgAbi<'tcx, Ty<'tcx>>,
callee_abi: &ArgAbi<'tcx, Ty<'tcx>>,
) -> bool {
let primitive_abi_compat = |a1: abi::Primitive, a2: abi::Primitive| -> bool {
match (a1, a2) {
// For integers, ignore the sign.
(abi::Primitive::Int(int_ty1, _sign1), abi::Primitive::Int(int_ty2, _sign2)) => {
int_ty1 == int_ty2
}
// For everything else we require full equality.
_ => a1 == a2,
}
};
// Heuristic for type comparison.
let layout_compat = || {
if caller_abi.layout.ty == callee_abi.layout.ty {
@ -267,28 +277,24 @@ fn check_argument_compat(
// 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...
return false;
}
// The rest *should* be okay, but we are extra conservative.
// This is tricky. Some ABIs split aggregates up into multiple registers etc, so we have
// to be super careful here. For the scalar ABIs we conveniently already have all the
// newtypes unwrapped etc, so in those cases we can just compare the scalar components.
// Everything else we just reject for now.
match (caller_abi.layout.abi, callee_abi.layout.abi) {
// Different valid ranges are okay (once we enforce validity,
// that will take care to make it UB to leave the range, just
// like for transmute).
// Different valid ranges are okay (the validity check will complain if this leads
// to invalid transmutes).
(abi::Abi::Scalar(caller), abi::Abi::Scalar(callee)) => {
caller.primitive() == callee.primitive()
primitive_abi_compat(caller.primitive(), callee.primitive())
}
(
abi::Abi::ScalarPair(caller1, caller2),
abi::Abi::ScalarPair(callee1, callee2),
) => {
caller1.primitive() == callee1.primitive()
&& caller2.primitive() == callee2.primitive()
primitive_abi_compat(caller1.primitive(), callee1.primitive())
&& primitive_abi_compat(caller2.primitive(), callee2.primitive())
}
// Be conservative
// Be conservative.
_ => false,
}
};
@ -309,7 +315,7 @@ fn check_argument_compat(
return true;
};
let mode_compat = || match (&caller_abi.mode, &callee_abi.mode) {
(PassMode::Ignore, PassMode::Ignore) => true,
(PassMode::Ignore, PassMode::Ignore) => true, // can still be reached for the return type
(PassMode::Direct(a1), PassMode::Direct(a2)) => arg_attr_compat(a1, a2),
(PassMode::Pair(a1, b1), PassMode::Pair(a2, b2)) => {
arg_attr_compat(a1, a2) && arg_attr_compat(b1, b2)
@ -326,7 +332,15 @@ fn check_argument_compat(
_ => false,
};
// We have to check both. `layout_compat` is needed to reject e.g. `i32` vs `f32`,
// which is not reflected in `PassMode`. `mode_compat` is needed to reject `u8` vs `bool`,
// which have the same `abi::Primitive` but different `arg_ext`.
if layout_compat() && mode_compat() {
// Something went very wrong if our checks don't even imply that the layout is the same.
assert!(
caller_abi.layout.size == callee_abi.layout.size
&& caller_abi.layout.align.abi == callee_abi.layout.align.abi
);
return true;
}
trace!(

27
src/tools/miri/tests/pass/function_calls/abi_compat.rs Normal file
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@ -0,0 +1,27 @@
use std::num;
use std::mem;
fn test_abi_compat<T, U>(t: T, u: U) {
fn id<T>(x: T) -> T { x }
// This checks ABI compatibility both for arguments and return values,
// in both directions.
let f: fn(T) -> T = id;
let f: fn(U) -> U = unsafe { std::mem::transmute(f) };
drop(f(u));
let f: fn(U) -> U = id;
let f: fn(T) -> T = unsafe { std::mem::transmute(f) };
drop(f(t));
}
fn main() {
test_abi_compat(0u32, 'x');
test_abi_compat(&0u32, &([true; 4], [0u32; 0]));
test_abi_compat(0u32, mem::MaybeUninit::new(0u32));
test_abi_compat(42u32, num::NonZeroU32::new(1).unwrap());
test_abi_compat(0u32, Some(num::NonZeroU32::new(1).unwrap()));
test_abi_compat(0u32, 0i32);
// Note that `bool` and `u8` are *not* compatible!
// One of them has `arg_ext: Zext`, the other does not.
}