1 .. -*- coding: utf-8; -*-

     2 .. include:: HEADER.rst

     3 

     4 ============

     5  Binary ABI

     6 ============

     7 .. contents::

     8    :local:

     9 

    10 Caller vs callee

    11 ================

    12 

    13 If routine A calls routine B then routine A is the caller and routine B is the

    14 callee. i.e. the caller is the routine which is calling the callee.

    15 

    16 The routine that initiates the call is the caller and the routine that is

    17 being called is is the callee.

    18 

    19 Argument vs parameter

    20 =====================

    21 

    22 From the perspective of the caller the thing which is passed is an argument.

    23 From the perspective of the routine that receives the call, i.e. the callee,

    24 the thing which is passed is a parameter.

    25 

    26 Linkage convention

    27 ==================

    28 

    29 A linkage convention is computing term that means an agreement which is made

    30 between a caller and a callee. The agreement describes:

    31 

    32  - how the caller should pass parameters to the callee

    33 

    34  - what assumptions the callee is allowed to make about the values in the

    35    machine registers at the moment of the call

    36 

    37  - who should preserve registers which are modified by the callee and/or which

    38    are important to the caller so that their original values are available

    39    when the caller needs them

    40 

    41  - how and where registers should be preserved

    42 

    43  - how the callee knows where to return to when it is ready to return to the

    44    caller

    45 

    46  - how the callee returns a value to the caller if the routine is a function

    47    (as opposed to a subroutine which has no return value)

    48 

    49  - how a debugger will find the information necessary to obtain a stack trace