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Question: Best way to share malloc/free in multiple modules? #579
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[-]Question: Best way to share malloc/free?[/-][+]Question: Best way to share malloc/free in multiple modules?[/+]on Apr 7, 2025 The closest thing would be wasi-sdk's currently experimental implementation of "dynamic" libraries. If you build with
-fPICand link with-shared, you can produce ".so" files. That said, you'll need a way to link the dynamic libraries together. If you're building a component, you can usewasm-tools component link. Otherwise, you may find the information here helpful for explaining how these libraries work and what would be needed to link them together.If you build with -fPIC and link with -shared, you can produce ".so" files.
I was doing this (see the working Makefile but I think the part I was missing was how to link them together, properly. The idea here for me is that I want to put the shared code (for example, my game engine and wasi-libc) in a seperate wasm loaded in host, then load the user's game, so they don't need to include all that in every game, rather than link it all together as one thing, to create the game (like static-linking works fine, but produces a lot of duplication.)
Otherwise, you may find the information here helpful
Yep, I followed that document's pattern to get my test project working. I may not have done it right, but that was the idea.
As I said, I did get it working with shared mem, the main prob was multiple definitions of malloc (if I load several wasi-sdk wasms) but otherwise it seems to work ok.
I tried this :
WASM_IMPORT(malloc) void* malloc(size_t size); WASM_IMPORT(free) void free(void* ptr); #define MALLOC_IMPL malloc #define FREE_IMPL free #include <stdlib.h>
If I build with this:
-fPIC -shared -Wl,--experimental-pic -Wl,--import-memoryI get this error at runtime:
[LinkError: WebAssembly.instantiate(): Import #5 "env" "sprintf": function import requires a callable]If I compile with
-Wl,--import-memoryIt all builds/runs fine, but doesn't seem to be copying the memory correctly (like my tests don't output the right stuff.)
You can see that on this branch
I have an example project that allows me to load multiple modules and share malloc/free (by implementing it in the host and sharing memory and a few other globals.)
I would like to do similar, but be able to use all of wasi-libc, so I can write "mostly just libc" code that shares memory between multiple modules.
What is the best way to do this? I have tried these so far:
MALLOC_IMPL?)