Generate Assembly Code using gcc or g++ Compiler

If you're learning how programs are translated into low-level instructions, or just curious about what the C or C++ code looks like at the assembly level, you can easily generate assembly code using gcc or g++ compiler. This knowledge is particularly useful for developers interested in optimization, debugging at the assembly level, or simply gaining a deeper understanding of how things work under the hood. This tutorial shows how to generate assembly code using gcc or g++ compiler.

Create the main.c file for testing:

#include <stdio.h>

int main() {
    printf("Hello world\n");

    return 0;
}

1. Basic assembly generation

Run command to generate assembly code:

gcc -S main.c

This command compiles the C source code into an assembly file called main.s. It stops the compilation process after generating the assembly and skips the linking stage. The same syntax applies for g++ compiler when generating assembly code for C++.

2. Output filename

To specify filename, use the -o option:

gcc -S main.c -o test.s

This does the same as above, but names the output file test.s instead of the default name.

3. Comments in assembly

Use the -fverbose-asm option to include extra comments in the assembly code, making it easier to understand what's going on:

gcc -S -fverbose-asm main.c

4. Intel syntax

By default, gcc or g++ compiler uses AT&T syntax for assembly. Use the -masm=intel option to switch to Intel syntax:

gcc -S -masm=intel main.c

5. Detailed annotated assembly

Use the -Wa,-adhln option to generate assembly with mixed source code, machine code, and assembly instructions all in one:

gcc -g -Wa,-adhln main.c > main.s

The -g option includes debug information.

6. Detailed annotated + verbose assembly

The following command combines all the features: debug info, source interleaving, and verbose comments:

gcc -g -Wa,-adhln -fverbose-asm main.c > main.s

It's one of the most detailed assembly views you can get using gcc or g++ compiler and is great for learning or inspection.