Foundations of Linux ARM64: Debug, Disassemble, and Reverse/

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GDB Disassembly Output – No Optimization

GDB Disassembly Output – No Optimization

Learn how to compile, load, and execute the GDB disassembly program, without code optimization.

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Arithmetic example in the C/C++ program

Let’s rewrite our arithmetic program in C/C++. Corresponding assembly language instructions are edited in the comments:

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int a, b;
int main(int argc, char* argv[])
{
    // Assign a value to variable a
    a = 1;          // adr x0,a   
                    // mov w1, #1
                    // str  w1, [x0]
    // Assign a value to variable b 
    b = 1;          // adr x0,b 
                    // mov w1, #1
                    // str  w1, [x0]
    // Add b and a and store in variable b
    b = b + a;      // adr x0,b 
                    // ldr w1, [x0]
                    // adr  x0, a
                    // ldr  w0, [x0]
                    // add  w1, w1, w0
                    // adr  x0, b
                    // str  w1, [x0]
    // Increment variable a by one
    ++a;            // adr x0, a 
                    // ldr w1, [x0]
                    // add  w1, w1, #1
                    // str  w1, [x0]
    // Multiply b with a and store into b
    b = b * a;      // adr x0,b 
                    // ldr w1, [x0]
                    // adr  x0, a
                    // ldr  w0, [x0]
                    // mul  w1, w1, w0
                    // adr  x0, b
                    // str  w1, [x0]
                    // results: [a] = 2 and [b] = 4
                
    // Return 0 means it executed successfully
    return 0; 
}

The flowchart below shows the working of the source code:

Disassembly in the no-optimization mode

It is easier to track the progress of our program during debugging if we can recompile without optimization.

Note: You can practice all the commands in the coding playground provided at the end of the lesson.

Compilation

If we compile and link the program in the no-optimization mode (default), as shown below, ...

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