callconventies

Call conventions, sometimes written as calling conventions, are a family of rules used by compilers, linkers, and languages to define how a program transfers control and data when calling functions. They specify how arguments are passed (which registers or stack slots), how the function’s return value is delivered, how the call stack is managed, and how names are decorated for linking. In some contexts the term may appear as callconventies, but the standard term is calling convention.

Key elements of a call convention include the parameter passing order, the choice between registers and stack for arguments, who is responsible for cleaning up the stack after a call, and how variadic functions are handled. They also cover rules for returning values, which registers may be used for that purpose, and which registers must be preserved across calls (caller-saved versus callee-saved).

Common conventions vary by platform and language. On 32-bit x86, well-known conventions include cdecl (arguments pushed on the stack right-to-left, caller cleans the stack), stdcall (callee cleans the stack), and fastcall (uses a mix of registers and stack). C++ member functions may use thiscall in some environments, reflecting the hidden this pointer. On 64-bit platforms, there are typically platform-specific ABIs: System V AMD64 (used by Linux and macOS) passes the first several integer or pointer arguments in registers, with the caller responsible for stack cleanup; Microsoft x64 (Windows) uses a similar approach but with its own register mappings and a shadow space for callees.

Interoperability between languages and libraries relies on matching call conventions. Mismatches can cause crashes or incorrect behavior, making adherence to the chosen convention essential in multiplatform development.