checkstop state does not halt the system, interrupts continue to be
serviced, and other CPUs run. Stop the machine with
qemu_system_guest_panicked.

Change the logging not to print separately to stderr because a
checkstop is a guest error (or perhaps a simulated machine error)
rather than a QEMU error. CPU registers are dumped.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
Since v1:
- Fix loop exit so it stops on the checkstop-causing instruction, rather than
  after it.

Since v2:
- Use qemu_system_guest_panicked rather than vm_stop (Richard)
- Move away from printing to stderr (Zoltan)
- Reduce changes to log messages.
---
 target/ppc/excp_helper.c | 27 +++++++++++++++++++--------
 1 file changed, 19 insertions(+), 8 deletions(-)

diff --git a/target/ppc/excp_helper.c b/target/ppc/excp_helper.c
index 1db6aaf7ee..022adc36c5 100644
--- a/target/ppc/excp_helper.c
+++ b/target/ppc/excp_helper.c
@@ -19,6 +19,8 @@
 #include "qemu/osdep.h"
 #include "qemu/main-loop.h"
 #include "qemu/log.h"
+#include "sysemu/sysemu.h"
+#include "sysemu/runstate.h"
 #include "cpu.h"
 #include "exec/exec-all.h"
 #include "internal.h"
@@ -427,20 +429,29 @@ static void powerpc_set_excp_state(PowerPCCPU *cpu, target_ulong vector,
 static void powerpc_mcheck_checkstop(CPUPPCState *env)
 {
     CPUState *cs = env_cpu(env);
+    FILE *f;
 
     if (FIELD_EX64(env->msr, MSR, ME)) {
         return;
     }
 
-    /* Machine check exception is not enabled. Enter checkstop state. */
-    fprintf(stderr, "Machine check while not allowed. "
-            "Entering checkstop state\n");
-    if (qemu_log_separate()) {
-        qemu_log("Machine check while not allowed. "
-                 "Entering checkstop state\n");
+    /*
+     * This stops the machine and logs CPU state without killing QEMU
+     * (like cpu_abort()) so the machine can still be debugged (because
+     * it is often a guest error).
+     */
+
+    f = qemu_log_trylock();
+    if (f) {
+        fprintf(f, "Entering checkstop state: "
+                   "machine check with MSR[ME]=0\n");
+        cpu_dump_state(cs, f, CPU_DUMP_FPU | CPU_DUMP_CCOP);
+        qemu_log_unlock(f);
     }
-    cs->halted = 1;
-    cpu_interrupt_exittb(cs);
+
+    qemu_system_guest_panicked(NULL);
+
+    cpu_loop_exit_noexc(cs);
 }
 
 static void powerpc_excp_40x(PowerPCCPU *cpu, int excp)
-- 
2.42.0