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🛠 x86 Assembly Reverse Engineering 🛠
Knowledge I have found interesting about the topic of x86 assembly.
⚙️ Basics ⚙️
| Intel Type | Bits | Name |
|---|---|---|
| - | 8 Bit | BYTE |
| 8086 | 16 Bit | WORD |
| i386 | 32 Bit | DWORD |
| x86 | 64 Bit | QWORD |
Meanings:
dword = DWORD = (double-word)
qword = QWORD = (quad-word)
NOTE: 📝
On 32 Bit ARM CPUs a WORD is 32 Bit.
🔧 x86 Registers 🔧
(Older Text from the University of Virginia Computer Science (2006), one of the best Guides for x86 Assembly)
Modern (i.e 386 and beyond) x86 processors have eight 32-bit general purpose registers, as depicted in Figure 1. The register names are mostly historical. For example, EAX used to be called the accumulator since it was used by a number of arithmetic operations, and ECX was known as the counter since it was used to hold a loop index. Whereas most of the registers have lost their special purposes in the modern instruction set, by convention, two are reserved for special purposes — the stack pointer (ESP) and the base pointer (EBP).
For the EAX, EBX, ECX, and EDX registers, subsections may be used. For example, the least significant 2 bytes of EAX can be treated as a 16-bit register called AX. The least significant byte of AX can be used as a single 8-bit register called AL, while the most significant byte of AX can be used as a single 8-bit register called AH. These names refer to the same physical register. When a two-byte quantity is placed into DX, the update affects the value of DH, DL, and EDX. These sub-registers are mainly hold-overs from older, 16-bit versions of the instruction set. However, they are sometimes convenient when dealing with data that are smaller than 32-bits (e.g. 1-byte ASCII characters).
When referring to registers in assembly language, the names are not case-sensitive. For example, the names EAX and eax refer to the same register.
In x86 registers have an 'e' in front of their name.
Example: eax, ebx, ecx, edx, ebp
Additional Info:
In x64 you have a 'r' instead.
Example: rax, rbx, rcx, rdx, rbp
You also have double-precision floating point going from xmm0 to xmm15.
🚩 EFLAGS 🚩
📝 Cheatsheet x86 Assembly 📝
Full Cheatsheet x86 Assembly, 20 Pages.
