usr/src/games/compat/modshell/compat.c

#include "defs.h"
#define BS 8
#define MAXARGS 300
short buf[BS];
/*
 *      Check for possible program to run under alternate runtime system
 *      If it checks out, start the rts and pass file and args
 *      Art Wetzel 3/13/80
 */
compat(file, argv, envp) char *file, *argv[], *envp[]; {
        register int fd;
        register char *rts;
        register char **nargv;
        char    *nargs[MAXARGS];
        /* alternate rts images must be readable */
        /* if not just go back and let rest of shell worry about it */
        if((fd = open(file,0))<0)
                return(0);
        /* read first BS pdp-11 words */
        if(read(fd,buf,sizeof buf) != sizeof buf) {
                close(fd);
                /* if can't, go back as it may be a short shell file */
                return(0);
        }
        close(fd);
        /* check type of image and set up run time system name */
        if(buf[0]==0407 || buf[0]==0410 || buf[0]==0411 || buf[0]==0405) {
                /* looks like UNIX a.out file */
                /* RTS or default rts */
                if((rts = rtsnod.namval) == 0)
                        rts = defrts;
                /* if header unused is set to 1 force version 6 */
                /* this is not a real difference between v6 and v7 a.outs */
                /* rather, version 6 a.outs were patched to be identifiable */
                if(buf[6] == 1)
                        rts = "/usr/bin/v6run";
        } else if(buf[6] == 0) {
                /* it looks like almost all RT-11 save images have 0 here */
                rts = "/usr/bin/rtrun";
        } else {
                /* was not a recognizable file type */
                return(0);
        }
        /* must make a new argv list with runtime system prefix */
        nargv = &nargs[0];
        *nargv++ = rts;
        /* have to pass full file name to rts */
        *nargv++ = file;
        argv++;
        while(*argv && nargv < &nargs[MAXARGS-1])
                *nargv++ = *argv++;
        /* force in final null */
        *nargv++ = (char *)0;
        /* try to start rts */
        execve(nargs[0], nargs, envp);
        /* if that failed, report no runtime system */
        failed(nargs[0], norts);
}