Allocation offset should be `usize`

[qinsoon]

We have the offset type as isize:

mmtk-core/src/util/alloc/allocator.rs

Line 157 in f828488

fn alloc(&mut self, size: usize, align: usize, offset: isize) -> Address;

However, in here, we specifically require offset to be positive:

mmtk-core/src/util/alloc/allocator.rs

Line 48 in f828488

debug_assert!(offset >= 0);

We should change the type of offset to usize instead.

[fepicture]

Hi, I am new to this repo and intend to do this one.
below is my understanding:

• replace all allocation offset to usize (those alloc wrappers all need to be changed)
• remove useless assert since we have move to positive offset

my question is do I need to add a unit test? alloc at a negative offset sounds a bit weird.

[qinsoon]

Thanks for your interest in contributing to MMTk.

Hi, I am new to this repo and intend to do this one. below is my understanding:

• replace all allocation offset to usize (those alloc wrappers all need to be changed)
• remove useless assert since we have move to positive offset

That's right.

my question is do I need to add a unit test? alloc at a negative offset sounds a bit weird.

I don't know what kind of test would explicitly test this change. Rust compiler can do a pretty good job here. So I don't feel a unit test is necessary for this change. However, we have some tests for different allocation alignments, and offset with different alignments. You can add more to it if you feel necessary: https://github.com/mmtk/mmtk-core/blob/master/vmbindings/dummyvm/src/tests/allocate_align_offset.rs

[fepicture]

thanks for your quick reply!
actually, I am also new to Rustc(hahaha :)
I have no other concerns and will start on this.