The primary difference between AT&T and Intel assembly syntax is the operand order. Intel syntax (destination first) is the native format for x86 processors used in Windows and official Intel manuals , while AT&T syntax (source first) is the default for GNU tools like GCC and GDB on Linux/Unix systems. [1, 2, 3]
Key Syntax Differences
| Feature [2, 4, 5, 6, 7] | Intel Syntax | AT&T Syntax |
|---|---|---|
| Operand Order | Opcode Dest, Src | Opcode Src, Dest |
| Register Prefix | None (e.g., eax) | % (e.g., %eax) |
| Immediate Value | None (e.g., 5) | $ (e.g., $5) |
| Size Suffixes | Explicit specifiers (dword ptr) | Suffixes on mnemonics (movl) |
| Memory Access | [base + index*scale + disp] | disp(base, index, scale) |
Detailed Breakdown
- Operand Direction: In Intel syntax, mov eax, 1 means “move 1 into eax” (reads like a variable assignment: eax = 1). In AT&T syntax, movl $1, %eax means “move 1 into eax” (reads like a function call or English sentence: “move 1 to eax”).
- Memory Addressing: Intel uses a mathematical expression inside brackets, which many find more intuitive. AT&T uses a comma-separated format where the displacement is outside the parentheses, e.g., 8(%ebp, %ecx, 4).
- Instruction Suffixes: AT&T uses a letter at the end of the instruction to denote data size: b (byte), w (word), l (long/32-bit), and q (quad/64-bit). Intel handles this with prefixes like byte ptr or qword ptr when the size is not clear from the registers. [2, 8, 9, 10, 11, 12]
Which One Should You Use?
- Use Intel if you are developing for Windows (MASM/NASM), doing reverse engineering (IDA Pro/Ghidra default to Intel), or following official Intel/AMD documentation .
- Use AT&T if you are writing inline assembly for GCC or Clang or working extensively in the Linux kernel where it is the established standard. [1, 8, 13, 14]
Note: Most modern tools allow you to switch. For example, in GDB, you can use set disassembly-flavor intel to see Intel syntax instead of the default AT&T. [8] Are you working on a specific project, like a Linux driver or a Windows application, that requires one of these?
- [1] https://stackoverflow.com
- [2] https://imada.sdu.dk
- [3] https://www.secureideas.com
- [4] https://www.reddit.com
- [5] https://news.ycombinator.com
- [6] https://www.freepascal.org
- [7] https://paul.bone.id.au
- [8] https://marcelofern.com
- [9] https://banisterfiend.wordpress.com
- [10] https://news.ycombinator.com
- [11] https://tuttlem.github.io
- [12] https://wiki.osdev.org
- [13] https://www.reddit.com
- [14] https://stackoverflow.com
