STACK(3)                       Library Routines                       STACK(3)




NAME

       _assertStack,    _beginStackCheck,   _endStackCheck,   _getStackBottom,
       _reportStack, __REPORT_STACK - report stack usage


SYNOPSIS

       #include <gno/gno.h>

       void _assertStack (unsigned int needed, int line, const char *file);
       void _beginStackCheck (void);
       int  _endStackCheck (void);
       unsigned int _getStackBottom (void);
       void _reportStack (void);
       void __REPORT_STACK (void);


DESCRIPTION

       The _beginStackCheck and _endStackCheck routines are intended to deter-
       mine  the  required  stack  usage  for a program during the development
       cycle.  _beginStackCheck should be called as soon as possible after the
       program  starts.  _endStackCheck should be called just prior to program
       exit.  _endStackCheck will return the number of bytes  of  stack  space
       used  by the program.  The result can then be used as a lower bound for
       the argument to occ's -s flag, or the stacksize pragma for ORCA/C.

       Since the procedure used by most programs is to  call  _beginStackCheck
       and  then  immediately  register with atexit(3) a function which prints
       the stack usage on  exit,  this  functionality  has  been  provided  by
       _reportStack; just call _reportStack immediately after main and nothing
       else  is  required.   Alternately,  you  may  also   call   the   macro
       __REPORT_STACK()  which resolves to a call to __reportStack if and only
       if the macro __STACK_CHECK__ is defined.

       The _getStackBottom routine returns  the  lowest  direct  page  address
       which can legally be used for the stack.  (The stack on the 65816 grows
       downward.)  This routine is used internally in libc and should not nor-
       mally be needed by an application.

       The  _assertStack  routine ensures that there are at least needed bytes
       left unused on the stack.  If this is not the case,  then  _assertStack
       prints  an  appropriate error message and calls exit(3) with a value of
       1.  This routine is intended for use when you have a function  that  is
       either directly or indirectly recursive, and you do not want to use the
       ORCA/C stack checking mechanism for every function in your source file.
       The  needed  number  of bytes is usually determined either through code
       inspection or empirically (lseg(1) is a good tool for assisting in this
       determination).   Either  way, you should probably make needed slightly
       larger than the value you expect to need.

       If file is non-NULL, then _assertStack will also  print  out  the  file
       name and line number as specified.  These values are available in any C
       program as the macros __FILE__ and __LINE__, respectively.


CAVEAT

       The _assertStack routine  itself  uses  stack  space,  especially  when
       printing out error messages.  Ensure you allow at least 100 bytes extra
       to allow for this.


EXAMPLE

       The most common way to make use of these routines is to  call  _report-
       Stack as your first step in main.  The GNO base sources make use of the
       macros __STACK_CHECK__ and __REPORT_STACK to  control  whether  or  not
       this check is done.  You may want to use the same macros.

         #include <gno/gno.h>

         void main (int argc, char **argv) {

           __REPORT_STACK();
           ... <program continues> ...

       The _assertStack routine is typically used in the following manner:

         #include <gno/gno.h>

         int recurse (int arg) {
           int i, j;

           /*
            * The value 350 was determined through code
            * inspection or with the help of lseg(1).
            */
           _assertStack(350, __LINE__, __FILE__);

           ... <routine continues> ...

           i = recurse(j);

           ... <routine continues> ...
           return i;
         }



AUTHORS

       Phillip Vandry <vandry@cam.org> Devin Reade <gdr@gno.org>


HISTORY

       The  _beginStackCheck  and  _endStackCheck  routines  first appeared as
       stand-along  object  file,  under  the  names   begin_stack_check   and
       end_stack_check.  They were first incorporated into GNO in v2.0.6.

       The  _getMinStack  and  _assertStack  routines  first  appeared  in GNO
       v2.0.6.


SEE ALSO

       lseg(1), occ(1), atexit(3), exit(3).
       The ORCA/C Reference Manual, Chapter 12.



GNO                              26 March 1998                        STACK(3)

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