compel: Add compel_run_at helper

Simply run tracee from specfied IP assuming
it's arelady have trapping instruction in
stream.

It's unsafe low-level function use with caution.

travis-ci: success for compel: A fix and new helper
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

compel/include/uapi/infect.h

@@ -73,6 +73,7 @@ extern int compel_syscall(struct parasite_ctl *ctl, int nr, unsigned long *ret,
 		unsigned long arg5,
 		unsigned long arg6);
 extern int compel_run_in_thread(struct parasite_thread_ctl *tctl, unsigned int cmd);
+extern int compel_run_at(struct parasite_ctl *ctl, unsigned long ip, user_regs_struct_t *ret_regs);
 
 /*
  * The PTRACE_SYSCALL will trap task twice -- on

compel/src/lib/infect.c

@@ -590,6 +590,17 @@ int compel_execute_syscall(struct parasite_ctl *ctl,
 	return err;
 }
 
+int compel_run_at(struct parasite_ctl *ctl, unsigned long ip, user_regs_struct_t *ret_regs)
+{
+	user_regs_struct_t regs = ctl->orig.regs;
+	int ret;
+
+	ret = parasite_run(ctl->rpid, PTRACE_CONT, ip, 0, &regs, &ctl->orig);
+	if (!ret)
+		ret = parasite_trap(ctl, ctl->rpid, ret_regs ? ret_regs : &regs, &ctl->orig);
+	return ret;
+}
+
 static int accept_tsock(struct parasite_ctl *ctl)
 {
 	int sock;