Integer overflow in AddrRange subset check

[georgehodgkins]

Describe the bug
If AddrRange A ends at the last byte of a 64-bit address space, it will be treated as a subset of any AddrRange B beginning at address 0. This is because A._end rolls over to zero, and so the check A._start >= B._start && A._end <= B._end becomes true.

Affects version
23.0.1.0

gem5 Modifications
I am working on modeling a novel memory device that requires specific allocation of the address space (which is why I encountered this error). But I have not made any changes to the AddrRange code, and the reproducible example below does not involve my device.

To Reproduce
Run this function and check the result:

bool checkAddrRangeBug() {
    AddrRange first_four_bytes = RangeSize(0x0, 4);
    AddrRange last_four_bytes = RangeSize(0xfffffffffffffffc, 4);
    return last_four_bytes.isSubset(first_four_bytes);
}

It returns true for me.

Expected behavior
The two ranges should be treated as distinct.

Host Operating System
Ubuntu 22.04 (kernel 5.15.90-wsl)

Host ISA
x86-64

Compiler used
gcc 11.3.0

[BobbyRBruce]

Thanks @georgehodgkins! We really appreciate the through bug report, it really saves us a lot of time.

I've created a draft PR, #242, in which i've added a test to our AddressRange Unit-test suite to reproduce this using your example. You're correct, this bug is real. I'll try to find someone to jump in and add a patch to this PR which fixes this bug.