1 -*- mode: outline; coding: utf-8 -*-

     2 

     3 * Caller vs callee.

     4 

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

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

     7 

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

     9 being called is is the callee.

    10 

    11 * Argument vs parameter.

    12 

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

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

    15 the thing which is passed is a parameter.

    16 

    17 * Linkage convention.

    18 

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

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

    21 

    22  - how the caller should pass parameters to the callee

    23 

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

    25    machine registers at the moment of the call

    26 

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

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

    29    when the caller needs them

    30 

    31  - how and where registers should be preserved

    32 

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

    34    caller

    35 

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

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

    38 

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