minix/lib/posix/_execve.c
2005-04-21 14:53:53 +00:00

115 lines
2.6 KiB
C
Executable file

/* execve() - basic program execution call Author: Kees J. Bot
* 21 Jan 1994
*/
#define _MINIX_SOURCE
#define nil 0
#define execve _execve
#define sbrk _sbrk
#include <lib.h>
#include <unistd.h>
#include <string.h>
#include <stddef.h>
int execve(const char *path, char * const *argv, char * const *envp)
{
char * const *ap;
char * const *ep;
char *frame;
char **vp;
char *sp;
size_t argc;
size_t frame_size;
size_t string_off;
size_t n;
int ov;
message m;
/* Assumptions: size_t and char *, it's all the same thing. */
/* Create a stack image that only needs to be patched up slightly
* by the kernel to be used for the process to be executed.
*/
ov= 0; /* No overflow yet. */
frame_size= 0; /* Size of the new initial stack. */
string_off= 0; /* Offset to start of the strings. */
argc= 0; /* Argument count. */
for (ap= argv; *ap != nil; ap++) {
n = sizeof(*ap) + strlen(*ap) + 1;
frame_size+= n;
if (frame_size < n) ov= 1;
string_off+= sizeof(*ap);
argc++;
}
for (ep= envp; *ep != nil; ep++) {
n = sizeof(*ep) + strlen(*ep) + 1;
frame_size+= n;
if (frame_size < n) ov= 1;
string_off+= sizeof(*ap);
}
/* Add an argument count and two terminating nulls. */
frame_size+= sizeof(argc) + sizeof(*ap) + sizeof(*ep);
string_off+= sizeof(argc) + sizeof(*ap) + sizeof(*ep);
/* Align. */
frame_size= (frame_size + sizeof(char *) - 1) & ~(sizeof(char *) - 1);
/* The party is off if there is an overflow. */
if (ov || frame_size < 3 * sizeof(char *)) {
errno= E2BIG;
return -1;
}
/* Allocate space for the stack frame. */
if ((frame = (char *) sbrk(frame_size)) == (char *) -1) {
errno = E2BIG;
return -1;
}
/* Set arg count, init pointers to vector and string tables. */
* (size_t *) frame = argc;
vp = (char **) (frame + sizeof(argc));
sp = frame + string_off;
/* Load the argument vector and strings. */
for (ap= argv; *ap != nil; ap++) {
*vp++= (char *) (sp - frame);
n= strlen(*ap) + 1;
memcpy(sp, *ap, n);
sp+= n;
}
*vp++= nil;
/* Load the environment vector and strings. */
for (ep= envp; *ep != nil; ep++) {
*vp++= (char *) (sp - frame);
n= strlen(*ep) + 1;
memcpy(sp, *ep, n);
sp+= n;
}
*vp++= nil;
/* Padding. */
while (sp < frame + frame_size) *sp++= 0;
/* We can finally make the system call. */
m.m1_i1 = strlen(path) + 1;
m.m1_i2 = frame_size;
m.m1_p1 = (char *) path;
m.m1_p2 = frame;
/* Clear unused fields */
m.m1_i3 = 0;
m.m1_p3 = NULL;
(void) _syscall(MM, EXEC, &m);
/* Failure, return the memory used for the frame and exit. */
(void) sbrk(-frame_size);
return -1;
}