Re: [RFC] AVR watchdog

[Michael Rolnik]

Hi Fred.

How can I reproduce it? 

Thank you. 

Michael Rolnik 

Sent from my cell phone, please ignore typos

On Wed, Apr 28, 2021, 5:17 PM Fred Konrad <konrad@adacore.com> wrote:

Hi,

I fall on a segfault while running the wdr instruction on AVR:

(gdb) bt
      #0  0x00005555add0b23a in gdb_get_cpu_pid (cpu=0x5555af5a4af0) at
        ../gdbstub.c:718
      #1  0x00005555add0b2dd in gdb_get_cpu_process (cpu=0x5555af5a4af0) at
        ../gdbstub.c:743
      #2  0x00005555add0e477 in gdb_set_stop_cpu (cpu=0x5555af5a4af0) at
        ../gdbstub.c:2742
      #3  0x00005555adc99b96 in cpu_handle_guest_debug (cpu=0x5555af5a4af0) at
        ../softmmu/cpus.c:306
      #4  0x00005555adcc66ab in rr_cpu_thread_fn (arg=0x5555af5a4af0) at
        ../accel/tcg/tcg-accel-ops-rr.c:224
      #5  0x00005555adefaf12 in qemu_thread_start (args=0x5555af5d9870) at
        ../util/qemu-thread-posix.c:521
      #6  0x00007f692d940ea5 in start_thread () from /lib64/libpthread.so.0
      #7  0x00007f692d6699fd in clone () from /lib64/libc.so.6

Wondering if there are some plan/on-going work to implement this watchdog?

---

Also meanwhile I though about a workaround like that:

diff --git a/target/avr/helper.c b/target/avr/helper.c
index 35e1019594..7944ed21f4 100644
--- a/target/avr/helper.c
+++ b/target/avr/helper.c
@@ -24,6 +24,7 @@
  #include "exec/exec-all.h"
  #include "exec/address-spaces.h"
  #include "exec/helper-proto.h"
+#include "sysemu/runstate.h"

  bool avr_cpu_exec_interrupt(CPUState *cs, int interrupt_request)
  {
@@ -191,7 +192,7 @@ void helper_wdr(CPUAVRState *env)
      CPUState *cs = env_cpu(env);

      /* WD is not implemented yet, placeholder */
-    cs->exception_index = EXCP_DEBUG;
+    qemu_system_reset_request(SHUTDOWN_CAUSE_GUEST_RESET);
      cpu_loop_exit(cs);
  }

In the case the guest wants to reset the board through the watchdog, would that
make sense to swap to that?

Best Regards,
Fred