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