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Make RPLs functional
This PR addresses two problems:
- LR isn't correctly restored in
__rpl_startleading to an endless loop or crash - wutmalloc calls
MEMGetSizeForMBlockExpHeapon pointers returned fromMEMAllocFromDefaultHeapfor realloc. But the underlying heap is not anExpHeapanymore. Thus any realloc call causes havoc.
I reworked wutmalloc to not assume any underlying heap implementation and instead add a header to each allocation to store the required information about size and alignment.
I also opted to add a canary value in the allocation header that is checked on each free/realloc operation. On corruption it will OSFatal(). I do believe that it's better to have controlled crashing with a message than to silently ignore it and crash further down the line. Even in release builds.
With these changes RPLs are functional. At least during my testing I have never encountered any problems.
On a side note, it may be wise to rename wut_malloc to wut_rpl_malloc in order to make it more clear that it's only used for RPLs. RPXs seem to use a custom sbrk based heap. If maintainers agree with this I can do a follow-up PR.
Worth mentioning without thinking about any implications yet: wutmalloc is currently used by plugins/modules in Aroma as well
On a side note, it may be wise to rename wut_malloc to wut_rpl_malloc in order to make it more clear that it's only used for RPLs. RPXs seem to use a custom sbrk based heap. If maintainers agree with this I can do a follow-up PR.
wutmalloc can be used by RPXs by overriding __preinit_user and calling __init_wut_malloc. This will cause wut_malloc.o to be linked in.
Is there any way we can fast path wutmalloc when the default heap is not overridden by the application, and avoid the overhead in that case?
We could add a boolean parameter to __init_wut_malloc which restores the old behavior of assuming ExpHeap. But then we have ABI breakage and two separate code paths in every function so this feels a bit shoehorned.
I think a better approach would be to keep the original wut_malloc as-is and introduce wut_rpl_malloc specifically for the purpose of RPLs where the underlying heap implementation isn't known.