cdecl

Cdecl is a calling convention used by C and C++ on x86 processors that specifies how functions receive arguments, return values, and how the call stack is managed. Under cdecl, function arguments are pushed onto the stack from right to left, and the caller is responsible for cleaning the stack after the call. The callee should not adjust the stack pointer to remove arguments.

Return values: for most integer and pointer types, the result is returned in the EAX register. Floating-point results may be returned in an FPU register or an SSE register depending on the compiler and ABI. The exact handling of larger or structure returns depends on the platform and compiler.

Register usage and prologue/epilogue: the callee must preserve certain registers (commonly EBX, ESI, EDI, and EBP) across calls, while other registers are caller-saved. A typical function prologue uses a stack frame (push EBP; mov EBP, ESP; sub ESP, ...), and the epilogue restores the frame and returns (leave; ret). Because the caller cleans the stack, the callee does not know how many arguments were passed, enabling variadic functions.

Variadic support: cdecl is well suited for functions with a variable number of arguments, such as printf, since the caller controls stack cleanup and argument counting.

Platform notes: cdecl is mainly associated with 32-bit x86 code and is widely supported by compilers like GCC and Clang, as well as many environments in the past. On 64-bit platforms, modern ABIs (such as System V AMD64 and Windows x64) use different conventions, and cdecl is not the default there. Symbol naming and decoration can vary by compiler and platform, but the convention itself centers on who cleans the stack and how arguments are passed.

In summary, cdecl defines a widely used, flexible model for x86 function calls, emphasizing right-to-left argument passing, caller-managed stack cleanup, and consistent return value handling.