WASM binary size with -sMAIN_MODULE 7 to 9 times heavier

[mho22]

Based on issue #23683.

Version of emscripten/emsdk:

emcc (Emscripten gcc/clang-like replacement + linker emulating GNU ld) 4.0.5 (53b38d0c6f9fce1b62c55a8012bc6477f7a42711)
clang version 21.0.0git (https:/github.com/llvm/llvm-project 553da9634dc4bae215e6c850d2de3186d09f9da5)
Target: wasm32-unknown-emscripten
Thread model: posix
InstalledDir: /root/emsdk/upstream/bin

I got a similar problem while including a heavy 46Mb file instead of using a char array. But I will use it to compare the two results

Former sample program from previous issue:

#include <stdio.h>

char test[1024*1024*50];

int main(void)
{
    puts(test);
    return 0;
}

Compiler command line and results:

emcc -o test.wasm -O3 -sMAIN_MODULE=0 -sTOTAL_MEMORY=200MB test.c

-rw-r--r-- 1 root root  171 Oct  3 06:18 test.c
-rwxr-xr-x 1 root root 2.0K Oct  3 06:18 test.wasm

emcc -o test.wasm -O3 -sMAIN_MODULE=1 -sTOTAL_MEMORY=200MB test.c

-rw-r--r-- 1 root root  171 Oct  3 06:18 test.c
-rwxr-xr-x 1 root root 1.6M Oct  3 06:19 test.wasm

emcc -o test.wasm -O3 -sMAIN_MODULE=2 -sTOTAL_MEMORY=200MB test.c

-rw-r--r-- 1 root root  171 Oct  3 06:18 test.c
-rwxr-xr-x 1 root root 8.3K Oct  3 06:20 test.wasm

The -sMAIN_MODULE=2 here will reduce the size significantly even if it is 4 times heavier than in the static linking. This is expected.

However, I tried something different for my issue :

New sample program:

#include <stdio.h>
#include "data_file.c"

int main(void)
{
    puts((const char *)php_magic_database);
    return 0;
}

The data_file.c is the PHP fileinfo extension libmagic database php_magic_database : https://github.com/php/php-src/blob/PHP-8.3.25/ext/fileinfo/data_file.c. It is 46Mb.

Compiler command line and results:

emcc -o test.wasm -O3 -sMAIN_MODULE=0 -sTOTAL_MEMORY=200MB test.c

-rw-r--r-- 1 root root  46M Oct  3 06:35 data_file.c
-rw-r--r-- 1 root root  168 Oct  3 06:37 test.c
-rwxr-xr-x 1 root root 1.2M Oct  3 06:37 test.wasm

emcc -o test.wasm -O3 -sMAIN_MODULE=1 -sTOTAL_MEMORY=200MB test.c

-rw-r--r-- 1 root root  46M Oct  3 06:35 data_file.c
-rw-r--r-- 1 root root  168 Oct  3 06:37 test.c
-rwxr-xr-x 1 root root 9.2M Oct  3 06:37 test.wasm

emcc -o test.wasm -O3 -sMAIN_MODULE=2 -sTOTAL_MEMORY=200MB test.c

-rw-r--r-- 1 root root  46M Oct  3 06:35 data_file.c
-rw-r--r-- 1 root root  168 Oct  3 06:37 test.c
-rwxr-xr-x 1 root root 7.6M Oct  3 06:41 test.wasm

While for the first experiment we had : 2Kb, then 1.6Mb, then 8kb, now we have from 1.2Mb, 9.2Mb and 7.6Mb. Is there a way to approach the 1.2Mb ? If not, is it possible to statically link that specific file because I know this file won't be used by other modules ?

I need to build my file with MAIN_MODULE since it will have other SIDE_MODULE during runtime load. But I also would like some heavy files to be significantly reduced like the data_file.c since it is only used in my MAIN_MODULE.

Do you know a way to achieve this ?