linux-user/hppa: clear the PSW 'N' bit when delivering signals

qemu-hppa may crash when delivering a signal. It can be demonstrated with
this program. Compile the program with "hppa-linux-gnu-gcc -O2 signal.c"
and run it with "qemu-hppa -one-insn-per-tb a.out". It reports that the
address of the flag is 0xb4 and it crashes when attempting to touch it.

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <signal.h>

sig_atomic_t flag;

void sig(int n)
{
	printf("&flag: %p\n", &flag);
	flag = 1;
}

int main(void)
{
	struct sigaction sa;
	struct itimerval it;

	sa.sa_handler = sig;
	sigemptyset(&sa.sa_mask);
	sa.sa_flags = SA_RESTART;
	if (sigaction(SIGALRM, &sa, NULL)) perror("sigaction"), exit(1);

	it.it_interval.tv_sec = 0;
	it.it_interval.tv_usec = 100;
	it.it_value.tv_sec = it.it_interval.tv_sec;
	it.it_value.tv_usec = it.it_interval.tv_usec;

	if (setitimer(ITIMER_REAL, &it, NULL)) perror("setitimer"), exit(1);

	while (1) {
	}
}

The reason for the crash is that the signal handling routine doesn't clear
the 'N' flag in the PSW. If the signal interrupts a thread when the 'N'
flag is set, the flag remains set at the beginning of the signal handler
and the first instruction of the signal handler is skipped.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Acked-by: Helge Deller <deller@gmx.de>
Cc: qemu-stable@nongnu.org
Signed-off-by: Helge Deller <deller@gmx.de>

linux-user/hppa/signal.c

@@ -159,6 +159,7 @@ void setup_rt_frame(int sig, struct target_sigaction *ka,
     }
     env->iaoq_f = haddr;
     env->iaoq_b = haddr + 4;
+    env->psw_n = 0;
     return;
 
  give_sigsegv: