$hp is initialised to incorrect value.

[otrho]

At VM initialization it says:

$hp = VM_MAX_RAM - 1: the heap area begins at the top and is empty to start.

It makes more sense for $hp to be initialised to just VM_MAX_RAM. It always essentially points to either non-addressable memory or previously allocated buffers (via ALOC), both of which are essentially 'reserved'.

[adlerjohn]

This change would avoid having to offset the value by 1 to use allocated memory, right?

[otrho]

Yep. Doing an aloc would be just:

let buf_addr = asm(size: size) {
    aloc size;
    hp: u64
}

...as per the discussion in FuelLabs/sway#1627

[adlerjohn]

@Voxelot is there general consensus to go forward with this change?

[Voxelot]

There is from the client-team side. @otrho also mentioned that the sway team could make a future-compatible workaround so that this change won't immediately break previously compiled code as well. But this workaround may not be needed if we do the change sooner.