pushing a value (not necessarily stored in a register) means writing it to the stack. popping means restoring whatever is on top of the stack into a register. Those are basic instructions: push 0xdeadbeef ; push a value to the stack pop eax ; eax is now 0xdeadbeef ; swap contents of registers push eax … Read more
SI = Source Index DI = Destination Index As others have indicated, they have special uses with the string instructions. For real mode programming, the ES segment register must be used with DI and DS with SI as in movsb es:di, ds:si SI and DI can also be used as general purpose index registers. For … Read more
Yes, it is more efficient. The opcode is shorter than mov eax, 0, only 2 bytes, and the processor recognizes the special case and treats it as a mov eax, 0 without a false read dependency on eax, so the execution time is the same.
The dword ptr part is called a size directive. This page explains them, but it wasn’t possible to direct-link to the correct section. Basically, it means “the size of the target operand is 32 bits”, so this will bitwise-AND the 32-bit value at the address computed by taking the contents of the ebp register and … Read more
You can switch to assembly layout in GDB: (gdb) layout asm See here for more information. The current assembly instruction will be shown in assembler window. ┌───────────────────────────────────────────────────────────────────────────┐ │0x7ffff740d756 <__libc_start_main+214> mov 0x39670b(%rip),%rax #│ │0x7ffff740d75d <__libc_start_main+221> mov 0x8(%rsp),%rsi │ │0x7ffff740d762 <__libc_start_main+226> mov 0x14(%rsp),%edi │ │0x7ffff740d766 <__libc_start_main+230> mov (%rax),%rdx │ │0x7ffff740d769 <__libc_start_main+233> callq *0x18(%rsp) │ >│0x7ffff740d76d <__libc_start_main+237> mov … Read more
Machine code is binary (1’s and 0’s) code that can be executed directly by the CPU. If you open a machine code file in a text editor you would see garbage, including unprintable characters (no, not those unprintable characters 😉 ). Object code is a portion of machine code not yet linked into a complete … Read more