************************************************************************* * * * DSTART.S modifi‚ : Startup module for C programs using dLibs * * * ************************************************************************* * * entry points * .globl __base ; basepage pointer .globl __start ; startup entry point .globl _etext ; end of text segment .globl _edata ; end of data segment .globl _end ; end of BSS segment (end of program) .globl __break ; location of stack/heap break .globl __exit ; terminate immediately with exit code .globl __argc ; number of arguments .globl __argv ; argument list pointer .globl __envp ; environment string pointer .globl _errno ; system error number .globl _gemdos ; trap #1 (gemdos) hook .globl _bios ; trap #13 (bios) hook .globl _xbios ; trap #14 (xbios) hook .globl _bdos ; trap #2 (bdos) hook * * external references * .globl __STKSIZ ; Stack size value from C (unsigned long) ; .globl __main ; Initial entry point for C program .globl _main ; C program main() function * * useful constants * MINSTK equ 1024 ; Minimum 1K stack size MARGIN equ 512 ; Minimum memory to return to OS * * GEMDOS functions * Cconws equ $09 ; Console write string Pterm equ $4C ; Process terminate (with exit code) Mshrink equ $4A ; Shrink program space * * basepage offsets * p_hitpa equ $04 ; top of TPA p_tbase equ $08 ; base of text p_tlen equ $0C ; length of text p_dbase equ $10 ; base of data p_dlen equ $14 ; length of data p_bbase equ $18 ; base of BSS p_blen equ $1C ; length of BSS p_env equ $2C ; environment string p_cmdlin equ $80 ; command line image * * STARTUP ROUTINE (must be first object in link) * text * * save initial stack and basepage pointers * __start: move.l sp,a5 ; a5 = initial stack pointer move.l 4(sp),a4 ; a4 = basepage address move.l a4,__base move.l p_tbase(a4),d3 add.l p_tlen(a4),d3 move.l d3,_etext ; end of text segment move.l p_dbase(a4),d3 add.l p_dlen(a4),d3 move.l d3,_edata ; end of data segment move.l p_bbase(a4),d3 add.l p_blen(a4),d3 move.l d3,_end ; end of BSS (end of program) move.l d3,__break ; set initial _break value move.l p_env(a4),__envp ; save environment pointer * * calculate free space available to program * move.l __break,d3 move.l d3,a3 ; a3 = base of free space neg.l d3 add.l p_hitpa(a4),d3 sub.l #MARGIN,d3 ; d3 = free space * * calculate new stack size (store in d2) * move.l #__STKSIZ,a2 ; a2 = &_STKSIZ move.l (a2),d2 ; if __STKSIZ is undefined beq minimum ; use MINSTK bpl setstk ; use __STKSIZ add.l d3,d2 ; if __STKSIZ is negative cmp.l #MINSTK,d2 ; try (free space + __STKSIZ) bge setstk ; if < MINSTK minimum: move.l #MINSTK,d2 ; use MINSTK * * check to see if there is enough room for requested stack * setstk: cmp.l d3,d2 blt shrink ; if (available < requested) move.l #stkerr,-(sp) move.w #Cconws,-(sp) trap #1 ; report a stack error addq.l #6,sp move.w #-39,-(sp) move.w #Pterm,-(sp) trap #1 ; and return error -39 (ENSMEM) * * set up new stack pointer and Mshrink * shrink: add.l a3,d2 ; new stack = free base + stack size move.l d2,sp sub.l a4,d2 ; keep space = new stack - __base move.l d2,-(sp) move.l a4,-(sp) clr.w -(sp) move.w #Mshrink,-(sp) trap #1 ; Mshrink(0, _base, keep); add.l #12,sp * * call C entry point function _main() * jsr _main * * void _exit(code) * int code; * * Terminate process with a return value of * __exit: ;tst.l (sp)+ ; pop return PC off the stack move.w #Pterm,-(sp) ; leaving trap #1 ; and terminate. * * operating system trap hooks for C * * long gemdos(function, [parameter, ...]) * int function; * _gemdos: move.l (sp)+,traprtn ; save return address trap #1 ; do gemdos trap bra chkstk * * long bios(function, [parameter, ...]) * int function; * _bios: move.l (sp)+,traprtn ; save return address trap #13 ; do bios trap bra chkstk * * long xbios(function, [parameter, ...]) * int function; * _xbios: move.l (sp)+,traprtn ; save return address trap #14 ; do xbios trap bra chkstk * * int bdos(function, parameter) * int function; * long parameter; * _bdos: move.l (sp),traprtn ; save return address move.l a6,(sp) ; save old frame pointer move.l sp,a6 ; set up frame pointer tst.l -(a6) ; (fake "link a6,#0") move.w 8(a6),d0 ; function code in D0.W move.l 10(a6),d1 ; parameter value in D1.L trap #2 ; do bdos trap move.l (sp)+,a6 ; restore old frame pointer * * check for stack overflow (done after all OS traps) * chkstk: cmp.l __break,sp bgt nosweat ; if (_break > sp) move.l #stkovf,-(sp) move.w #Cconws,-(sp) trap #1 ; report a stack overflow addq.l #6,sp move.w #-1,-(sp) move.w #Pterm,-(sp) trap #1 ; and return error -1 (ERROR) nosweat: move.l traprtn,-(sp) ; else, restore return address rts ; and do a normal return. * * this call to _main ensures that it the user's main() function will be * linked, even if it is in a library. * jsr _main ; NO PATH TO THIS STATEMENT * THE FOLLOWING IS SELF MODIFYING CODE, DO NOT DISTURB move.l #$644c6962,$7320(sp) moveq.l #$31,d3 move.l $0(a2,d0),d7 * * initialized data space * .data .even stkerr: .dc.b 'Not enough memory',$d,$a,0 stkovf: .dc.b 'Stack overflow',$d,$a,0 _errno: .dc.w 0 ; system error number __argc: .dc.w 0 ; number of command line args __argv: .dc.l 0 ; pointer to command line arg list * * uninitialized data space * .bss .even __base: .ds.l 1 ; pointer to basepage _etext: .ds.l 1 ; pointer to end of text segment _edata: .ds.l 1 ; pointer to end of data segment _end: .ds.l 1 ; pointer to end of BSS (end of program) __break: .ds.l 1 ; pointer to stack/heap break __envp: .ds.l 1 ; pointer to environment string traprtn: .ds.l 1 ; storage for return PC in trap hooks end