Return convention in windows

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In the context of programming and calling conventions on Windows systems, the "return convention" refers to how functions return their results to the caller. Different programming languages and compilers follow specific conventions to ensure that values are returned correctly and consistently.

Here are some common return conventions used on Windows:

  1. x86 and x64 Calling Conventions:
    On Windows, two primary calling conventions are used for x86 (32-bit) and x64 (64-bit) architectures: cdecl and stdcall.

    • cdecl (C Calling Convention): This is the default convention for most C and C++ functions. In this convention, the caller is responsible for cleaning up the stack after the function call. Function arguments are pushed onto the stack in reverse order, and the return value (if any) is placed in the EAX register.

    • stdcall (Standard Calling Convention): In this convention, the called function is responsible for cleaning up the stack after the call. Function arguments are pushed onto the stack in reverse order, and the return value is placed in the EAX register. stdcall is commonly used for Windows API functions.

  2. Return Value and Registers:
    The return value of a function is typically stored in a designated register. For example, in the cdecl convention on x86, the return value is stored in the EAX register. In the stdcall convention, the return value is also stored in the EAX register.

  3. Structure Return:
    When a function returns a complex data type like a structure, the caller and callee must agree on how the data will be returned. Some conventions pass a hidden pointer to the caller, and the caller is responsible for providing memory for the returned structure.

  4. Floating-Point Return:
    For floating-point return values, the FPU or XMM registers may be used to store the result, depending on the calling convention.

It's important to note that these conventions are defined by the compiler and platform, and different languages and compilers might have variations. When writing code in different programming languages or interacting with external libraries, it's crucial to understand the calling convention being used to ensure correct function calls and result handling.

For more specific information about calling conventions, you should refer to the documentation of the compiler or development environment you are using.