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Foundations of Linux ARM64: Debug, Disassemble, and Reverse

Disassembly Output in the Code Optimization Mode

Explore how compiler optimization flags such as -O1, -O2, and -O3 affect the disassembly output of C/C++ programs on Linux ARM64. Understand how to use GDB commands to disassemble optimized code, investigate register and memory interactions, and recognize how separate compilation impacts variable initialization. Practice compiling with optimization and analyzing the resulting assembly to deepen your debugging and reverse engineering skills.

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Disassembly output with optimization

We can add flags for optimizing the code while compiling our source file. A flag -O is used for the optimization of code, and the -O1 flag further optimizes the code size and execution time. There are other flags for optimization, such as -O2 and -O3, which reduce the code size and execution time even more.

Source code

Here, we give a C/C++ code for our project of reconstructing a program through the GDB disassembly output in the optimization mode.

C++
int a, b;
int *pa, *pb;
int main(int argc, char* argv[])
{
	pa = &a;
	pb = &b;
	*pa = 1;
	*pb = 1;
	*pb = *pb + *pa;
	++*pa;
	*pb = *pb * *pa;
	return 0;
}
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