************************************************************************* * * * DSTART.S 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 __start: * * save initial stack and basepage pointers * 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 * * call C function to get command line arguments * lea.l p_cmdlin(a4),a0 * get pointer to command line image move.b (a0)+,d0 ext.w d0 * extract length move.w d0,-(sp) * cmdlen move.l a0,-(sp) * cmdline jsr __initar * call _initargs(cmdline, cmdlen) addq.l #6,sp * * 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 move.l (a2),d2 * if __STKSIZ is positive 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 * if _main returns move.w d0,4(sp) * insert return value and fall thru * * 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 $0(a2,d0),d7 * * initialized data space * .data .even stkerr: * not enough memory for stack .dc.b 'Not enough memory',$d,$a,0 stkovf: * impending stack overflow .dc.b 'Stack overflow',$d,$a,0 _errno: * system error number .dc.w 0 __argc: * number of command line args .dc.w 0 __argv: * pointer to command line arg list .dc.l 0 * * uninitialized data space * .bss .even __base: * pointer to basepage .ds.l 1 _etext: * pointer to end of text segment .ds.l 1 _edata: * pointer to end of data segment .ds.l 1 _end: * pointer to end of BSS (end of program) .ds.l 1 __break: * pointer to stack/heap break .ds.l 1 __envp: * pointer to environment string .ds.l 1 traprtn: * storage for return PC in trap hooks .ds.l 1 .end