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fix overflow error in signed wrapping offset

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Ralf Jung 2019-05-26 14:12:54 +02:00
parent 082da0c698
commit 3defb3f18f
1 changed files with 27 additions and 24 deletions
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51
src/librustc/mir/interpret/pointer.rs
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@ -20,11 +20,35 @@ pub trait PointerArithmetic: layout::HasDataLayout {
self.data_layout().pointer_size
}
//// Trunace the given value to the pointer size; also return whether there was an overflow
/// Helper function: truncate given value-"overflowed flag" pair to pointer size and
/// update "overflowed flag" if there was an overflow.
/// This should be called by all the other methods before returning!
#[inline]
fn truncate_to_ptr(&self, val: u128) -> (u64, bool) {
fn truncate_to_ptr(&self, (val, over): (u64, bool)) -> (u64, bool) {
let val = val as u128;
let max_ptr_plus_1 = 1u128 << self.pointer_size().bits();
((val % max_ptr_plus_1) as u64, val >= max_ptr_plus_1)
((val % max_ptr_plus_1) as u64, over || val >= max_ptr_plus_1)
}
#[inline]
fn overflowing_offset(&self, val: u64, i: u64) -> (u64, bool) {
let res = val.overflowing_add(i);
self.truncate_to_ptr(res)
}
// Overflow checking only works properly on the range from -u64 to +u64.
#[inline]
fn overflowing_signed_offset(&self, val: u64, i: i128) -> (u64, bool) {
// FIXME: is it possible to over/underflow here?
if i < 0 {
// Trickery to ensure that i64::min_value() works fine: compute n = -i.
// This formula only works for true negative values, it overflows for zero!
let n = u64::max_value() - (i as u64) + 1;
let res = val.overflowing_sub(n);
self.truncate_to_ptr(res)
} else {
self.overflowing_offset(val, i as u64)
}
}
#[inline]
@ -33,32 +57,11 @@ pub trait PointerArithmetic: layout::HasDataLayout {
if over { err!(Overflow(mir::BinOp::Add)) } else { Ok(res) }
}
#[inline]
fn overflowing_offset(&self, val: u64, i: u64) -> (u64, bool) {
let (res, over1) = val.overflowing_add(i);
let (res, over2) = self.truncate_to_ptr(u128::from(res));
(res, over1 || over2)
}
#[inline]
fn signed_offset<'tcx>(&self, val: u64, i: i64) -> EvalResult<'tcx, u64> {
let (res, over) = self.overflowing_signed_offset(val, i128::from(i));
if over { err!(Overflow(mir::BinOp::Add)) } else { Ok(res) }
}
// Overflow checking only works properly on the range from -u64 to +u64.
#[inline]
fn overflowing_signed_offset(&self, val: u64, i: i128) -> (u64, bool) {
// FIXME: is it possible to over/underflow here?
if i < 0 {
// trickery to ensure that i64::min_value() works fine
// this formula only works for true negative values, it panics for zero!
let n = u64::max_value() - (i as u64) + 1;
val.overflowing_sub(n)
} else {
self.overflowing_offset(val, i as u64)
}
}
}
impl<T: layout::HasDataLayout> PointerArithmetic for T {}