Support `mprotect` in wasi-emulated-mman

Question

Support `mprotect` in wasi-emulated-mman

Closed this issue 6 months ago · 6 comments

Is there any interest in supporting mprotect in the emulation library? The main utility would be to compile programming language runtimes that link, but not execute at runtime, a JIT (what prompted me to write the issue was LLVM, similar to #447).

I think the semantics should be that mapping in-bounds memory is only possible as PROT_READ|PROT_WRITE, and out-of-bounds memory as PROT_NONE.

Answer 1 · 2024-05-20T16:37:11.000Z

That sounds reasonable to me. I'm not sure about the PROT_NONE case because memory.grow can cause previously out-of-bounds memory to become in-bounds, but allowing PROT_READ|PROT_WRITE for in-bounds memory sounds fine.

Answer 2 · 2024-05-20T16:38:48.000Z

How do you find out the current memory size from C?

Answer 3 · 2024-05-20T16:42:34.000Z

__builtin_wasm_memory_size(0) returns the number of 64KiB pages currently allocated (in memory 0).

Answer 4 · 2024-05-20T16:45:33.000Z

Thanks. Do you think mprotect should require the address to be page-aligned, or should it accept just any? I'm leaning towards the latter since it's a stub anyways.

Answer 5 · 2024-05-21T01:30:48.000Z

It looks like POSIX requires the address to be page-aligned so I chose to do that.

Answer 6 · 2024-05-22T17:10:06.000Z

This is now implemented in #500.