Abstract mmap/munmap behind platform guards for WASM and embedded targets#50
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lancejpollard wants to merge 1 commit intoHigherOrderCO:mainfrom
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Abstract mmap/munmap behind platform guards for WASM and embedded targets#50lancejpollard wants to merge 1 commit intoHigherOrderCO:mainfrom
lancejpollard wants to merge 1 commit intoHigherOrderCO:mainfrom
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…gets Add #ifdef guards to sys/mmap_anon.c and sys/munmap_anon.c that fall back to calloc/free on platforms without mmap (__EMSCRIPTEN__ or HVM_NO_MMAP). Uses calloc to preserve mmap's zero-initialization guarantee. Existing behavior on POSIX platforms is unchanged.
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Adds
#ifdefguards tosys/mmap_anon.candsys/munmap_anon.cthat fall back tocalloc/freewhen__EMSCRIPTEN__orHVM_NO_MMAPis defined.Benefits
Why calloc (not malloc)
mmap(MAP_ANONYMOUS)returns zero-initialized pages. Several callers depend on this:uset_inituses the allocation as a bitset (all bits must start clear), and the heap is expected to start zeroed.callocpreserves this guarantee.Note on lazy allocation
mmapwithMAP_NORESERVEallocates virtual address space lazily (physical pages allocated on first access).callocdoes not have this property. On platforms using this fallback,HEAP_CAPshould be reduced to a size that fits in physical memory.Changes
Two files, 29 lines added, 0 removed from existing code paths. The existing mmap code is wrapped in
#elseand is unchanged.clang/sys/mmap_anon.c:calloc(1, bytes)fallbackclang/sys/munmap_anon.c:free(ptr)fallbackRisk
Don't think there are any on existing platforms. Guards only trigger when
__EMSCRIPTEN__orHVM_NO_MMAPis defined. Neither is defined in normal desktop/server builds. All existing tests pass.