Supplying a memory instance to a function before execution about pywasm

[mohanson]

It is very difficult for us to maintain the memory structure myself. The more I suggest is by importing external functions such as:

Source C code

char data[1024] = {};

extern int load_data(int addr_from, int addr_to);

int main() { 
  load_data(&data[0], &data[1023]);
  return data[0];
}

Compile C to wasm program

(module
 (type $FUNCSIG$iii (func (param i32 i32) (result i32)))
 (import "env" "load_data" (func $load_data (param i32 i32) (result i32)))
 (table 0 anyfunc)
 (memory $0 1)
 (export "memory" (memory $0))
 (export "main" (func $main))
 (func $main (; 1 ;) (result i32)
  (drop
   (call $load_data
    (i32.const 16)
    (i32.const 1039)
   )
  )
  (i32.load8_s offset=16
   (i32.const 0)
  )
 )
)

And used in pywasm as

import pywasm


your_data = [4 for i in range(1024)]

def load_data(ctx: pywasm.Ctx, addr_from: int, addr_to: int):
    ctx.memory_list[0].data[addr_from:addr_to] = your_data
    return 0

runtime = pywasm.load('/tmp/program.wasm', {'env': {'load_data': load_data}})
r = runtime.exec('main', [])
print(r)  # 4

[void4]

Nice! I think it might also work this way:

data = [1,2,3,4,5]

gamestate = pywasm.Memory(pywasm.binary.MemoryType())
gamestate.grow(len(data))

for figindex, fig in enumerate(data):
gamestate.data[figindex] = fig

runtime = pywasm.load(path, {
	'env': {
		'abort': env_abort,
		"gamestate": gamestate
	}
}, opts=option)

[mohanson]

You did not use it correctly. The memory is managed by your program. For example, if your program uses alloc to apply for a block of memory (always starting from address 0), then this will overwrite your initial data.

[mohanson]

Where you should write data to the memory, this information should always come from your program, let it decide.

[void4]

In this case, I may have to inject the function call manually somehow if I did it this way.

The AssemblyScript compiler seems to have an --importMemory flag (also here), which imports env.memory. But I didn't get it to work yet, it fails with

		runtime = pywasm.load(path, {
			'env': {
				'abort': env_abort,
				"memory": gamestate
			}
		}, opts=option)

Traceback (most recent call last):
  File "main.py", line 131, in <module>
    value = runWasm(players[board.turn], board)
  File "main.py", line 46, in runWasm
    runtime = pywasm.load(path, {
  File "/home/one/.pyenv/versions/3.8.2/lib/python3.8/site-packages/pywasm/__init__.py", line 99, in load
    return Runtime(module, imps, opts)
  File "/home/one/.pyenv/versions/3.8.2/lib/python3.8/site-packages/pywasm/__init__.py", line 57, in __init__
    self.machine.instantiate(module, extern_value_list)
  File "/home/one/.pyenv/versions/3.8.2/lib/python3.8/site-packages/pywasm/execution.py", line 1984, in instantiate
    assert match_memory(a, b)

You are probably right, but I'll try it this way one more time

[void4]

Okay, I give up my alternative attempt, your solution works, and probably saves memory too. Thank you :)

[prescod]

So is it impossible to supply memories as inputs? I ran into the same exception void4 did when I tried it.