elf2dmp: Don't abandon when Prcb is set to 0

Prcb may be set to 0 for some CPUs if the dump was taken before they
start. The dump may still contain valuable information for started CPUs
so don't abandon conversion in such a case.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Viktor Prutyanov <viktor.prutyanov@phystech.edu>
Message-id: 20230611033434.14659-1-akihiko.odaki@daynix.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

contrib/elf2dmp/main.c

@@ -316,6 +316,11 @@ static int fill_context(KDDEBUGGER_DATA64 *kdbg,
             return 1;
         }
 
+        if (!Prcb) {
+            eprintf("Context for CPU #%d is missing\n", i);
+            continue;
+        }
+
         if (va_space_rw(vs, Prcb + kdbg->OffsetPrcbContext,
                     &Context, sizeof(Context), 0)) {
             eprintf("Failed to read CPU #%d ContextFrame location\n", i);