wasi | Experimental WASI API bindings for Rust | Binary Executable Format library

In wasi-libc, the function signature of __wasi_fd_read is:

Firstly, if you are doing multi-threading with emscripten then each thread will already have its own stack and its own value for __stack_pointer. Thats is part of what defines a thread.

If you still want to manipulate the stack yourself (perhaps to have many stacks within a single thread) then you can use the emscripten helper functions stackSave (to get the SP of the current thread) and stackRestore (to set the SP of the current thread).

If you are not using emscripten at all, then you are in uncharted territory (what runtime are using using? how are you starting new threads?), but the simplest way to do stack pointer manipulation would be with assembly code. See how emscripten implements these functions:

https://github.com/emscripten-core/emscripten/blob/main/system/lib/compiler-rt/stack_ops.S

So you could do something like this:

I see nothing wrong with that. Targeting 32bits means that the memory addressing is 32bits. For this reason before the memory store instruction, all you have are 32bit instructions (i.e. the offset and the value are i32) you have this at some point:

Compilers will often inline functions and remove code that isn't used, this is why your C program ends up with everything inside a _start function. As explained in the FAQ you may list functions to export using emcc -s EXPORTED_FUNCTIONS=_main,_matrix in order to prevent them from being inlined or removed. Adding this results in a wasm module with the function correctly exported.

As for running functions directly, the source code for wasmer run has logic to determine which runtime environment should be exposed to the module. However, if you pass -i function, it entirely skips the environment setup and runs your function directly. In this case, the modules fails to initialize because it imports functions from WASI (in order to write things to the console, and get the current clock time).

I believe the reason why wasm32-unknown-unknown works is that it doesn't link to any runtime, and implements dummy interfaces for things that it can't simulate (all filesystem calls result in errors, etc.)

In summary, wasmer run -i function isn't meant to run functions from modules that have imports, it might be possible to patch wasmer-cli for that, but I'm not sure if it would work across all runtime environments.

If you want to use WASI then the way to pass args to main is to implement the wasi_snapshot_preview1.args_get and wasi_snapshot_preview1.args_sizes_get syscalls which are used by WASI programs to access the argv values. In that case you would want to call _start rather than main.

If you want to bypass that and call main directly you would need to somehow allocate and array of char * pointers in the linear memory which you could then pass as your argv value. The problem that you face if you try to take this approach is that allocating memory (e.g. via malloc) before calling main is hard. My advise would be to go with the first method which is to call _start and implement that wasi syscall needed to access argv. (You can call also then remove the -Wl,--no-entry from your link command).

When you want to create a linked list, you should use a struct Cell that contains two types of date: the first is your data itself (Contact in your case) the other is a pointer to the next cell in the list (next). Using this type of implementation you make your code more readable, modular and reusable.

Couple of problems:

1. The major problem is that there are two Contact *new = malloc(sizeof(Contact)); lines. One inside the loop and one outside. They are two different variables. The while loop condition is using the one outside the loop. Hence the fscanf is writing to the same memory for every loop. One way to fix that is to make the second instance just new = malloc(sizeof(Contact));. Note that this loop has a memory leak as the last allocated node is lost - left to you as an exercise to fix.

2. searching_contact has an infinete loop as the if (strcmp(name, cursor->name) == 0) block is missing a break.

Yes it is implemented in all runtimes implementing wasi. The reason is that this feature is related to import/export mechanism of WebAssembly.

As a rule, a WHERE clause of SELECT .. FOR XML .. shoud make the subquery depend on exactly the same columns which are listed in the GROUP BY clause of the outer query. Try