Let’s try to answer in order! The data section contains anything that you want to be automatically initialized for you by the system before it calls the entry point of your program. You’re right, normally global variables end up here. Zero-initialized data is generally not included in the executable file, since there’s no reason to … Read more
When the function is called, the stack looks like: +————-+ | Parameter 2 | +————-+ | Parameter 1 | +————-+ | Return Addr | <– esp +————-+ then after the “stack frame” is set up: +————-+ | Parameter 2 | <– [ebp + 12] +————-+ | Parameter 1 | <– [ebp + 8] +————-+ | … Read more
According to this, they are the same: The shift arithmetic left (SAL) and shift logical left (SHL) instructions perform the same operation; they shift the bits in the destination operand to the left (toward more significant bit locations). For each shift count, the most significant bit of the destination operand is shifted into the CF … Read more
On x86 the NOP instruction is XCHG AX, AX The 2 mnemonic instructions assemble to the same binary op-code. (Actually, I suppose an assembler could use any xchg of a register with itself, but AX or EAX is what’s typically used for the nop as far as I know). xchg ax, ax has the properties … Read more
3.1.1.1 Opcode Column in the Instruction Summary Table (Instructions without VEX Prefix) The “Opcode” column in the table above shows the object code produced for each form of the instruction. When possible, codes are given as hexadecimal bytes in the same order in which they appear in memory. Definitions of entries other than hexadecimal bytes … Read more
leal, or lea full name is “Load effective address” and it does exactly this: It does an address calculation. In your example the address calculation is very simple, because it just adds a offset to ebx and stores the result in eax: eax = ebx + 0x10 lea can do a lot more. It can … Read more
Assuming 32-bit x86, use the following function: get_eip: mov eax, [esp] ret Then, to get the value of EIP in EAX, simply: call get_eip
MM registers are the registers used by the MMX instruction set, one of the first attempts to add (integer-only) SIMD to x86. They are 64 bit wide and they are actually aliases for the mantissa parts of the x87 registers (but they are not affected by the FPU top of the stack position); this was … Read more
The square brackets essentially work like a dereference operator (e.g., like * in C). So, something like mov REG, x moves the value of x into REG, whereas mov REG, [x] moves the value of the memory location where x points to into REG. Note that if x is a label, its value is the … Read more
The direction flag is used to influence the direction in which string instructions offset pointer registers. These are the same instructions that can be used with the REP prefix to repeat the operation. (Although lods isn’t very useful with rep). The string instructions are: MOVS (copy mem to mem), STOS (store AL/AX/EAX/RAX), SCAS (scan string), … Read more