ptrace: change tracehook_report_syscall_exit() to handle stepping

Suggested by Roland.

Change tracehook_report_syscall_exit() to look at step flag and send the
trap signal if needed.

This change affects ia64, microblaze, parisc, powerpc, sh.  They pass
nonzero "step" argument to tracehook but since it was ignored the tracee
reports via ptrace_notify(), this is not right and not consistent.

	- PTRACE_SETSIGINFO doesn't work

	- if the tracer resumes the tracee with signr != 0 the new signal
	  is generated rather than delivering it

	- If PT_TRACESYSGOOD is set the tracee reports the wrong exit_code

I don't have a powerpc machine, but I think this test-case should see the
difference:

	#include <unistd.h>
	#include <sys/ptrace.h>
	#include <sys/wait.h>
	#include <assert.h>
	#include <stdio.h>

	int main(void)
	{
		int pid, status;

		if (!(pid = fork())) {
			assert(ptrace(PTRACE_TRACEME) == 0);
			kill(getpid(), SIGSTOP);

			getppid();

			return 0;
		}

		assert(pid == wait(&status));
		assert(ptrace(PTRACE_SETOPTIONS, pid, 0, PTRACE_O_TRACESYSGOOD) == 0);

		assert(ptrace(PTRACE_SYSCALL, pid, 0,0) == 0);
		assert(pid == wait(&status));

		assert(ptrace(PTRACE_SINGLESTEP, pid, 0,0) == 0);
		assert(pid == wait(&status));

		if (status == 0x57F)
			return 0;

		printf("kernel bug: status=%X shouldn't have 0x80\n", status);
		return 1;
	}

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: <linux-arch@vger.kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/tracehook.h

@@ -134,6 +134,13 @@ static inline __must_check int tracehook_report_syscall_entry(
  */
 static inline void tracehook_report_syscall_exit(struct pt_regs *regs, int step)
 {
+	if (step) {
+		siginfo_t info;
+		user_single_step_siginfo(current, regs, &info);
+		force_sig_info(SIGTRAP, &info, current);
+		return;
+	}
+
 	ptrace_report_syscall(regs);
 }