= Application binary interface
An <application binary interface> specifies the conventions that separately compiled program components must share to cooperate at the binary level. It includes a <calling convention>, representations and layout of data, and platform conventions for <object files>. A common source-language declaration alone does not ensure that the generated <machine instructions> agree on where arguments and results reside.
For example, Microsoft's x64 <calling convention> passes the first two integer arguments in the <processor registers> `RCX` and `RDX`, and returns a suitable scalar integer result in `RAX`.<x64 Calling Convention by Microsoft>[Parameter passing, integer row; Return values, scalar values fitting in 64 bits]{ref} A caller placing `7` and `5` in different <processor registers> from those expected by the called function can obtain the wrong result even if both sides describe an addition function. Matching the <application binary interface> allows a <compiler> and hand-written <assembly language> to cooperate; it does not require them to use the same internal implementation.
Back to article page
