lib/libc/sys-minix/execve.c

   1 /*      execve() - basic program execution call         Author: Kees J. Bot
   2  *                                                              21 Jan 1994
   3  */
   4 #define _MINIX_SOURCE
   5
   6 #include <sys/cdefs.h>
   7 #include "namespace.h"
   8 #include <lib.h>
   9
  10 #include <unistd.h>
  11 #include <string.h>
  12 #include <stddef.h>
  13 #include <sys/exec_elf.h>
  14
  15 #ifdef __weak_alias
  16 __weak_alias(execve, _execve)
  17 #endif
  18
  19 int execve(const char *path, char * const *argv, char * const *envp)
  20 {
  21         char * const *ap;
  22         char * const *ep;
  23         char *frame;
  24         char **vp;
  25         char *sp;
  26         size_t argc;
  27         int extra;
  28         int vectors;
  29         size_t frame_size;
  30         size_t string_off;
  31         size_t n;
  32         int ov;
  33         message m;
  34
  35         /* Assumptions: size_t and char *, it's all the same thing. */
  36
  37         /* Create a stack image that only needs to be patched up slightly
  38          * by the kernel to be used for the process to be executed.
  39          */
  40
  41         ov= 0;                  /* No overflow yet. */
  42         frame_size= 0;          /* Size of the new initial stack. */
  43         string_off= 0;          /* Offset to start of the strings. */
  44         argc= 0;                /* Argument count. */
  45
  46         for (ap= argv; *ap != NULL; ap++) {
  47                 n = sizeof(*ap) + strlen(*ap) + 1;
  48                 frame_size+= n;
  49                 if (frame_size < n) ov= 1;
  50                 string_off+= sizeof(*ap);
  51                 argc++;
  52         }
  53
  54         for (ep= envp; *ep != NULL; ep++) {
  55                 n = sizeof(*ep) + strlen(*ep) + 1;
  56                 frame_size+= n;
  57                 if (frame_size < n) ov= 1;
  58                 string_off+= sizeof(*ap);
  59         }
  60
  61         /* Add an argument count, two terminating nulls and
  62          * space for the ELF aux vectors, that must come before
  63          * (i.e. at a higher address) then the strings.
  64          */
  65         vectors = sizeof(argc) + sizeof(*ap) + sizeof(*ep) +
  66                 sizeof(AuxInfo) * PMEF_AUXVECTORS;
  67         extra = vectors + PMEF_EXECNAMELEN1;
  68         frame_size+= extra;
  69         string_off+= extra;
  70
  71         /* Align. */
  72         frame_size= (frame_size + sizeof(char *) - 1) & ~(sizeof(char *) - 1);
  73
  74         /* The party is off if there is an overflow. */
  75         if (ov || frame_size < 3 * sizeof(char *)) {
  76                 errno= E2BIG;
  77                 return -1;
  78         }
  79
  80         /* Allocate space for the stack frame. */
  81         if ((frame = (char *) sbrk(frame_size)) == (char *) -1) {
  82                 errno = E2BIG;
  83                 return -1;
  84         }
  85
  86         /* Set arg count, init pointers to vector and string tables. */
  87         * (size_t *) frame = argc;
  88         vp = (char **) (frame + sizeof(argc));
  89         sp = frame + string_off;
  90
  91         /* Load the argument vector and strings. */
  92         for (ap= argv; *ap != NULL; ap++) {
  93                 *vp++= (char *) (sp - frame);
  94                 n= strlen(*ap) + 1;
  95                 memcpy(sp, *ap, n);
  96                 sp+= n;
  97         }
  98         *vp++= NULL;
  99
 100         /* Load the environment vector and strings. */
 101         for (ep= envp; *ep != NULL; ep++) {
 102                 *vp++= (char *) (sp - frame);
 103                 n= strlen(*ep) + 1;
 104                 memcpy(sp, *ep, n);
 105                 sp+= n;
 106         }
 107         *vp++= NULL;
 108
 109         /* Padding. */
 110         while (sp < frame + frame_size) *sp++= 0;
 111
 112         /* Clear unused message fields */
 113         memset(&m, 0, sizeof(m));
 114
 115         /* We can finally make the system call. */
 116         m.m1_i1 = strlen(path) + 1;
 117         m.m1_i2 = frame_size;
 118         m.m1_p1 = (char *) __UNCONST(path);
 119         m.m1_p2 = frame;
 120
 121         /* Tell PM/VFS we have left space for the aux vectors
 122          * and executable name
 123          */
 124         m.PMEXEC_FLAGS = PMEF_AUXVECTORSPACE | PMEF_EXECNAMESPACE1;
 125
 126         (void) _syscall(PM_PROC_NR, EXEC, &m);
 127
 128         /* Failure, return the memory used for the frame and exit. */
 129         (void) sbrk(-frame_size);
 130         return -1;
 131 }