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Annotation of pmsdk/samples/notes/cswitch, revision 1.1

1.1     ! root        1: When compiling a C program for PM, here are some points to note:
        !             2: ----------------------------------------------------------------
        !             3: 
        !             4: Segment setup
        !             5: -------------
        !             6: 
        !             7: There are 3 switches which specify segment setup (note that SS never changes):
        !             8: 
        !             9: -Ad    SS==DS.
        !            10:        SS and DS are loaded with the same value when the program
        !            11:        starts up and are assumed to be the same later on.
        !            12:        This is the default.
        !            13: 
        !            14: -Aw    SS!=DS, DS not reloaded on function entry.
        !            15:        SS is not assumed to equal DS, so if DS must contain the same value
        !            16:        as SS for some operation, DS is pushed, loaded, used and popped.
        !            17: 
        !            18: -Au    SS!=DS, DS reloaded on function entry, for all functions.
        !            19:        At the beginning of each function, DS is pushed
        !            20:        then loaded with the module's data segment (usually DGROUP).
        !            21:        At the end of each function, DS is popped.  Also, any other
        !            22:        time DS must be changed, it is pushed, loaded, used and popped.
        !            23:        The _loadds keyword has the same effect, but on a
        !            24:        function-by-function basis.
        !            25: 
        !            26: If you have a thread whose stack lies outside the default data segment
        !            27: (eg. obtained by a call to DosAllocSeg, or if you compile large-model and
        !            28: use malloc()), you must specify SS!=DS.  Multi-threaded apps nearly always
        !            29: have SS!=DS.
        !            30: 
        !            31: Any routine which is called by code which uses a different data segment
        !            32: (different value in DS) must use the _loadds keyword.  Your program will
        !            33: execute correctly if you use the -Au switch, but this switch generates DS
        !            34: save, load and restore code for all functions, even ones which use the same
        !            35: data segment.  Generally, only window procedures or dll entry points need
        !            36: this code.
        !            37: 
        !            38: Summary:
        !            39: If your program has multiple threads
        !            40:        Use the -Aw switch
        !            41: Else
        !            42:        Use the -Ad switch
        !            43: 
        !            44: Use the _loadds keyword when declaring window procedures and dll entry points.
        !            45: 
        !            46: 
        !            47: 
        !            48: Window procedures
        !            49: -----------------
        !            50: 
        !            51: The preferred method of typing window procedures is to use the
        !            52: CALLBACK keyword, defined in os2def.h:
        !            53: 
        !            54: #define CALLBACK pascal far _loadds
        !            55: 
        !            56: Note that window procedures need not be exported in PM (unlike Windows).
        !            57: 
        !            58: The -Gw switch should not be used for PM application programs, since it
        !            59: causes unnecessary code to be emitted. It will not cause incorrect
        !            60: execution, but it is wasteful.
        !            61: 
        !            62: 
        !            63: 
        !            64: C switches used in the samples
        !            65: ------------------------------
        !            66: 
        !            67: -Zi    causes symbolic information used by CodeView to be generated
        !            68: 
        !            69: -Zp    packs structure members
        !            70: 
        !            71: -Gs    turns off stack checking.  Useful if SS!=DS and C runtime libraries
        !            72:        are used.
        !            73: 
        !            74: -G2    causes 286 instructions to be generated
        !            75: 
        !            76: -Gc    makes the Pascal calling convention the default
        !            77: 
        !            78: -Od    disables optimization.  Useful when running CodeView.
        !            79: 
        !            80: -NT    sets the name of the text (code) segment
        !            81: 
        !            82: -c     compiles without linking
        !            83: 
        !            84: -u     removes definitions of all predefined identifiers
        !            85: 
        !            86: -J     changes the default type for char from signed to unsigned
        !            87: 
        !            88: -W3    sets the compiler output warning level to its most sensitive

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