WebAssembly: How to Allocate Your Allocator

nullprogram.com

45 pointsingve3 comments

> (If only Clang had some sort of “noinit” variable attribute in order to allow heap to be uninitialized…)

It's attribute((loader_uninitialized)), e.g. https://github.com/llvm/llvm-project/blob/main/clang/test/Se...

Though I'll note that (AFAIK) WASM environments don't expose access to uninitialized memory. When you grow your Memory object the new space is zeroed, and when you allocate it initially it's zeroed. This can actually show up in profilers when you examine application startup time.

loader_uninitialized would hopefully address the zeroes in the module at least...

I wonder if the WASM runtimes still clear pages that were just requested from the OS. These should be already filled with zeroes, and at least on Linux you could even let the pages be lazy loaded (all WASM runtimes I know of on 64-bit Linux use an ~8GB virtual memory guard region, so all the fresh WASM pages will always be fresh OS pages as well).

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