Currently, if the default `MBLOCK_SHIFT` is changed for wasm target, there are roughly 100 new test failures. This is not ideal and should be fixed some time in the future, for the following reasons: - On any platform, the `MBLOCK_SHIFT` literal ought to be the single source of truth, and changing it should only affect performance of compiled code, not correctness. - The default mblock size may not be ideal for wasm32. A smaller one may make more sense, e.g. changing it to page-sized (65536) will make it possible to drop a `wasi-libc` patch; also making it more practical to run the wasm in a rather resource-constrained runtime. Below is one place that violates the single source of truth principle for `MBLOCK_SHIFT`, and there's likely more out there that ought to be fixed. ```diff --- a/rts/sm/HeapAlloc.h +++ b/rts/sm/HeapAlloc.h @@ -64,7 +64,7 @@ extern struct mblock_address_range mblock_address_space; extern StgWord8 mblock_map[]; /* On a 32-bit machine a 4KB table is always sufficient */ -# define MBLOCK_MAP_SIZE 4096 +# define MBLOCK_MAP_SIZE (1 << (32 - MBLOCK_SHIFT)) # define MBLOCK_MAP_ENTRY(p) ((StgWord)(p) >> MBLOCK_SHIFT) # define HEAP_ALLOCED(p) mblock_map[MBLOCK_MAP_ENTRY(p)] # define HEAP_ALLOCED_GC(p) HEAP_ALLOCED(p) ```