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/* Code sample: using ptrace for simple tracing of a child process.
**
** Note: this was originally developed for a 32-bit x86 Linux system; some
** changes may be required to port to x86-64.
**
** Eli Bendersky (http://eli.thegreenplace.net)
** This code is in the public domain.
*/
#include <stdio.h>
#include <stdarg.h>
#include <stdlib.h>
#include <signal.h>
#include <syscall.h>
#include <sys/ptrace.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/reg.h>
#include <sys/user.h>
#include <unistd.h>
#include <errno.h>
/* Print a message to stdout, prefixed by the process ID
*/
void procmsg(const char* format, ...)
{
va_list ap;
fprintf(stdout, "[%d] ", getpid());
va_start(ap, format);
vfprintf(stdout, format, ap);
va_end(ap);
}
void run_target(const char* programname)
{
procmsg("target started. will run '%s'\n", programname);
/* Allow tracing of this process */
if (ptrace(PTRACE_TRACEME, 0, 0, 0) < 0) {
perror("ptrace");
return;
}
/* Replace this process's image with the given program */
execl(programname, programname, 0);
}
void run_debugger(pid_t child_pid)
{
int wait_status;
unsigned icounter = 0;
procmsg("debugger started\n");
/* Wait for child to stop on its first instruction */
wait(&wait_status);
while (WIFSTOPPED(wait_status)) {
icounter++;
struct user_regs_struct regs;
ptrace(PTRACE_GETREGS, child_pid, 0, &regs);
unsigned instr = ptrace(PTRACE_PEEKTEXT, child_pid, regs.eip, 0);
procmsg("icounter = %u. EIP = 0x%08x. instr = 0x%08x\n",
icounter, regs.eip, instr);
/* Make the child execute another instruction */
if (ptrace(PTRACE_SINGLESTEP, child_pid, 0, 0) < 0) {
perror("ptrace");
return;
}
/* Wait for child to stop on its next instruction */
wait(&wait_status);
}
procmsg("the child executed %u instructions\n", icounter);
}
int main(int argc, char** argv)
{
pid_t child_pid;
if (argc < 2) {
fprintf(stderr, "Expected a program name as argument\n");
return -1;
}
child_pid = fork();
if (child_pid == 0)
run_target(argv[1]);
else if (child_pid > 0)
run_debugger(child_pid);
else {
perror("fork");
return -1;
}
return 0;
}