What does the `cheerp-linear-heap-size` argument do?

I expected the argument cheerp-linear-heap-size to especify the initial heap size to give users control to define how much memory is allocated when starting execution. However, I tried to use the argument and the result was different from what I expected.

For exemple, I created a simple "Hello World" program test.c, and compilled it with cheerp-linear-heap-size=100:

/opt/cheerp/bin/clang -cheerp-linear-heap-size=100 -cheerp-pretty-code test.c -o test.js

After it, I inserted the statement console.log(__heap.byteLength); inside the function _start in the test.js file. This statement will print the initial size of the heap. The result is as fallows:

$ node test.js
1114112
hello world

The second line is the size of the heap, which is a little more than 1MB, I expected to be 100MB because I used cheerp-linear-heap-size=100. I want to understand why I got a different result and what does the cheerp-linear-heap-size argument do.

About my system:

$ uname -a
Linux raul 5.15.0-78-generic #85~20.04.1-Ubuntu SMP Mon Jul 17 09:42:39 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

$ /opt/cheerp/bin/clang --version
Cheerp 3.0-1~focal clang version 16.0.0
Target: cheerp-leaningtech-webbrowser-wasm
Thread model: posix
InstalledDir: /opt/cheerp/bin

Content of test.c:

#include <stdio.h>

int main() {
    printf("hello world\n");
    return 0;
}

leaningtech / cheerp-meta

What does the `cheerp-linear-heap-size` argument do? #155