c_reverse/week1/day1

Day 1: Variables, Memory, and the Stack

📝 Concepts Covered

Today we explored how high-level C variables are translated into low-level machine instructions and memory operations.

1. The Stack and RBP

Local variables in C are stored on the Stack. The CPU uses the RBP (Base Pointer) register as a reference point to find these variables.

• int a = 123; -> mov DWORD PTR [rbp-4], 0x7b

2. Register Basics (x64)

Registers are small, fast storage locations inside the CPU.

• RAX, RBX, RCX, RDX: General purpose 64-bit registers.
• EAX, EBX, ECX, EDX: The lower 32-bit halves of the above (used for int in C).

3. Data Sizes

The assembly instruction specifies how much data to move:

• BYTE PTR: 1 byte (char)
• WORD PTR: 2 bytes (short)
• DWORD PTR: 4 bytes (int)
• QWORD PTR: 8 bytes (long or pointers)

4. Arithmetic Pattern

CPUs perform arithmetic using a Load-Modify-Store cycle:

1. Load memory value into a register.
2. Add/Sub the register value.
3. Store the register result back into memory.

🛠 Exercises Completed

• exo_1.c: Basic assignment and hex identification.
• exo_2.c: Arithmetic deconstruction (The add instruction).
• exo_3.c: Data type sizes and memory offsets.