List of X86 Calling Conventions
This is a list of x86 calling conventions. These are conventions primarily intended for C/C++ compilers (especially the 64-bit part below), and thus largely special cases. Other languages may use other formats and conventions in their implementations.
| Architecture | Calling convention name | Operating system, compiler | Parameters in registers | Parameter order on stack | Stack cleanup by | Notes |
|---|---|---|---|---|---|---|
| 8086 | cdecl | RTL (C) | Caller | |||
| Pascal | LTR (Pascal) | Callee | ||||
| fastcall | Microsoft (non-member) | AX, DX, BX | LTR (Pascal) | Callee | Return pointer in BX. | |
| fastcall | Microsoft (member function) | AX, DX | LTR (Pascal) | Callee | “this” on stack low address. Return pointer in AX. | |
| fastcall | Borland compiler | AX, DX, BX | LTR (Pascal) | Callee | “this” on stack low address. Return pointer on stack high address. | |
| Watcom compiler | AX, DX, BX, CX | RTL (C) | Callee | Return pointer in SI. | ||
| IA-32 | cdecl | GCC | RTL (C) | Caller | When returning struct/class, the calling code allocates space and passes a pointer to this space via a hidden parameter on the stack. The called function writes the return value to this address. | |
| cdecl | Microsoft | RTL (C) | Caller | When returning struct/class,
|
||
| stdcall | RTL (C) | Callee | ||||
| GCC | RTL (C) | Hybrid | Stack aligned on 16 bytes boundary. | |||
| fastcall | Microsoft | ECX, EDX | RTL (C) | Callee | Return pointer on stack if not member function. | |
| fastcall | GCC | ECX, EDX | RTL (C) | Callee | ||
| fastcall | Borland/Embarcadero compiler | EAX, EDX, ECX | LTR (Pascal) | Callee | ||
| thiscall | Microsoft | ECX | RTL (C) | Callee | Default for member functions. | |
| Watcom compiler | EAX, EDX, EBX, ECX | RTL (C) | Callee | Return pointer in ESI. | ||
| x86-64 | Microsoft x64 calling convention | Windows (Microsoft Visual C++, Intel C++ Compiler, Embarcadero compiler), UEFI | RCX/XMM0, RDX/XMM1, R8/XMM2, R9/XMM3 | RTL (C) | Caller | Stack aligned on 16 bytes. 32 bytes shadow space on stack. The specified 8 registers can only be used for parameters 1 through 4. |
| System V AMD64 ABI | GNU/Linux, BSD, Mac OS X (GCC, Intel C++ Compiler) | RDI, RSI, RDX, RCX, R8, R9, XMM0–7 | RTL (C) | Caller | Stack aligned on 16 bytes boundary. Red zone below stack. |
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