build.sh

clang --target=wasm32 -std=c99 -emit-llvm -c main.c
llc -march=wasm32 -filetype=obj main.bc
wasm-ld --no-entry --export-all --allow-undefined -o test.wasm main.o

index.html

<script>

    const memory = new WebAssembly.Memory({
        initial: 1024,
        maximum: 4096,
    });

    var env =
    {
        memory: memory,

        ASSERT: (c) => {
            console.log("assert: " + c);
        }
    };

    const importObject = {
        env: env,
    };

    WebAssembly.instantiateStreaming(fetch("test.wasm", { credentials: "same-origin" }), importObject)
        .then(result => {

            console.log('JS: Loaded wasm file');

            const { exports } = result.instance;
            exports._start();
        })
        .catch(error => {
            console.error('there was some error; ', error)
        });
</script>

main.c

#include <stdbool.h>
#include <stddef.h>

extern void ASSERT(bool c);

void *memcpy(void *dest, const void * src, size_t n)
{
    unsigned char *d = dest;
    const unsigned char *s = src;

    for (; n; n--) *d++ = *s++;
    return dest;
}
void* memset(void* str, int c, size_t n)
{
    unsigned char* s = str;
    while (n--)
    {
        *s = c;
        s++;
    }
    return str;
}

struct Big
{
    char data[512000];
};

struct Contain
{
    int index;
    struct Big array[100];
    int test;

};
static struct Contain c;

static void add(struct Big val)
{
    c.array[c.index] = val;
    c.index += 1;
}

void _start()
{
    c.index = 0;
    c.test = 5;

    ASSERT(c.index == 0);
    ASSERT(c.test == 5);

    struct Big val = {};
    add(val);

    ASSERT(c.index == 1);
    ASSERT(c.test == 5);
}