assert that offset is in bounds for Arm64Call
@@ -85,11 +85,18 @@ impl CompiledBlob {
let base = get_address(name);
// The instruction is 32 bits long.
let iptr = at as *mut u32;
- let diff = (base as isize) - (at as isize);
+ // The offset encoded in the `bl` instruction is the
+ // number of bytes divided by 4.
+ let diff = ((base as isize) - (at as isize)) >> 2;
+ // Sign propagating right shift disposes of the
+ // included bits, so the result is expected to be
+ // either all sign bits or 0, depending on if the original
+ // value was negative or positive.
+ assert!((diff >> 26 == -1) || (diff >> 26 == 0));
// The lower 26 bits of the `bl` instruction form the
// immediate offset argument.
let chop = 32 - 26;
- let imm26 = ((diff >> 2) as u32) << chop >> chop;
+ let imm26 = (diff as u32) << chop >> chop;
unsafe { *iptr |= imm26; }
}
_ => unimplemented!(),
