usr/src/lib/csu/vax/crt0.c

static  char *sccsid = "@(#)crt0.c      4.4 (Berkeley) %G%";

/*
 *      C start up routine.
 *      Robert Henry, UCB, 20 Oct 81
 *
 *      We make the following (true) assumptions:
 *      1) when the kernel calls start, it does a jump to location 2,
 *      and thus avoids the register save mask.  We are NOT called
 *      with a calls!  see sys1.c:setregs().
 *      2) The only register variable that we can trust is sp,
 *      which points to the base of the kernel calling frame.
 *      Do NOT believe the documentation in exec(2) regarding the
 *      values of fp and ap.
 *      3) We can allocate as many register variables as we want,
 *      and don't have to save them for anybody.
 *      4) Because of the ways that asm's work, we can't have
 *      any automatic variables allocated on the stack, because
 *      we must catch the value of sp before any automatics are
 *      allocated.
 */

char **environ;

asm("#define _start start");
start()
{
        struct kframe {
                int     kargc;
                char    *kargv[1];      /* size depends on kargc */
                char    kargstr[1];     /* size varies */
                char    kenvstr[1];     /* size varies */
        };
        /*
         *      ALL REGISTER VARIABLES!!!
         */
        register int r11;               /* needed for init */
        register struct kframe *kfp;    /* r10 */
        register char **targv;
        register char **argv;

#ifdef lint
        kfp = 0;
#else not lint
        asm("   movl    sp,r10");       /* catch it quick */
#endif not lint
        for (argv = targv = &kfp->kargv[0]; *targv++; /* void */)
                /* void */ ;
        if (targv >= (char **)(*argv))
                --targv;
        environ = targv;
        exit(main(kfp->kargc, argv, environ));
}

/*
 * null mcount, just in case some routine is compiled for profiling
 */
asm("   .globl  mcount");
asm("mcount:    rsb");