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Debugging, Disassembly & Reversing in Linux for x64 Architecture

GDB Disassembly Output—Optimization

Explore how compiler optimization affects GDB disassembly output of a simple arithmetic C++ program. Learn to compile with optimization flags, use breakpoints, and interpret optimized assembly code to better understand code execution and memory changes.

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Disassembly with code optimization

Source code

The source code of the arithmetic program is given below:

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

The flowchart below shows the working of the source code:

Flowchart of the arithmetic program
Flowchart of the arithmetic program

Compilation

We can add certain flags to optimize the code while compiling our source file. The flag -O is used for the optimization of code and -O1 is an optimization flag that further optimizes the code size and execution time. There are other flags for optimization, such as -O2, and -O3, which reduce the size and execution time of the code even further. Now, let’s ...