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getargv.c
C
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/* Copied, Pasted and summarized from ps' source code.
You can use sysctl to get other process' argv.
*/
 
#include <sys/sysctl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define pid_of(pproc) pproc->kp_proc.p_pid
 
void print_argv_of_pid(int);
 
int
main(int argc, char** argv) {
if (argc != 2) {
fprintf(stderr, "Usage: %s pid\n", argv[0]);
exit(1);
}
print_argv_of_pid(atoi(argv[1]));
return 0;
}
 
void print_argv_of_pid(int pid) {
int mib[3], argmax, nargs, c = 0;
size_t size;
char *procargs, *sp, *np, *cp;
int show_args = 1;
 
fprintf(stderr, "Getting argv of PID %d\n", pid);
 
mib[0] = CTL_KERN;
mib[1] = KERN_ARGMAX;
 
size = sizeof(argmax);
if (sysctl(mib, 2, &argmax, &size, NULL, 0) == -1) {
goto ERROR_A;
}
 
/* Allocate space for the arguments. */
procargs = (char *)malloc(argmax);
if (procargs == NULL) {
goto ERROR_A;
}
 
 
/*
* Make a sysctl() call to get the raw argument space of the process.
* The layout is documented in start.s, which is part of the Csu
* project. In summary, it looks like:
*
* /---------------\ 0x00000000
* : :
* : :
* |---------------|
* | argc |
* |---------------|
* | arg[0] |
* |---------------|
* : :
* : :
* |---------------|
* | arg[argc - 1] |
* |---------------|
* | 0 |
* |---------------|
* | env[0] |
* |---------------|
* : :
* : :
* |---------------|
* | env[n] |
* |---------------|
* | 0 |
* |---------------| <-- Beginning of data returned by sysctl() is here.
* | argc |
* |---------------|
* | exec_path |
* |:::::::::::::::|
* | |
* | String area. |
* | |
* |---------------| <-- Top of stack.
* : :
* : :
* \---------------/ 0xffffffff
*/
mib[0] = CTL_KERN;
mib[1] = KERN_PROCARGS2;
mib[2] = pid;
 
 
size = (size_t)argmax;
if (sysctl(mib, 3, procargs, &size, NULL, 0) == -1) {
goto ERROR_B;
}
 
memcpy(&nargs, procargs, sizeof(nargs));
cp = procargs + sizeof(nargs);
 
/* Skip the saved exec_path. */
for (; cp < &procargs[size]; cp++) {
if (*cp == '\0') {
/* End of exec_path reached. */
break;
}
}
if (cp == &procargs[size]) {
goto ERROR_B;
}
 
/* Skip trailing '\0' characters. */
for (; cp < &procargs[size]; cp++) {
if (*cp != '\0') {
/* Beginning of first argument reached. */
break;
}
}
if (cp == &procargs[size]) {
goto ERROR_B;
}
/* Save where the argv[0] string starts. */
sp = cp;
 
/*
* Iterate through the '\0'-terminated strings and convert '\0' to ' '
* until a string is found that has a '=' character in it (or there are
* no more strings in procargs). There is no way to deterministically
* know where the command arguments end and the environment strings
* start, which is why the '=' character is searched for as a heuristic.
*/
for (np = NULL; c < nargs && cp < &procargs[size]; cp++) {
if (*cp == '\0') {
c++;
if (np != NULL) {
/* Convert previous '\0'. */
*np = ' ';
} else {
/* *argv0len = cp - sp; */
}
/* Note location of current '\0'. */
np = cp;
 
if (!show_args) {
/*
* Don't convert '\0' characters to ' '.
* However, we needed to know that the
* command name was terminated, which we
* now know.
*/
break;
}
}
}
 
/*
* sp points to the beginning of the arguments/environment string, and
* np should point to the '\0' terminator for the string.
*/
if (np == NULL || np == sp) {
/* Empty or unterminated string. */
goto ERROR_B;
}
 
/* Make a copy of the string. */
printf("%s\n", sp);
 
/* Clean up. */
free(procargs);
return;
 
ERROR_B:
free(procargs);
ERROR_A:
fprintf(stderr, "Sorry, failed\n");
exit(2);
}

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