kern, arm: Dump dmesg on kernel panic/oops

Add helper functions to dump the guest kernel's dmesg buffer to a text
file in m5out. This functionality is split into two parts. First, a
dmesg dump function that can be used in other places:

void Linux::dumpDmesg(ThreadContext *, std::ostream &)

This function is used to implement two PCEvents: DmesgDumpEvent and
KernelPanic event. The only difference between the two is that the
latter produces a gem5 panic instead of a warning in addition to
dumping the kernel log.

Change-Id: I6d2af1d666ace57124089648ea906f6c787ac63c
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Gabor Dozsa <gabor.dozsa@arm.com>

src/arch/arm/ArmSystem.py

@@ -98,6 +98,14 @@ class LinuxArmSystem(GenericArmSystem):
     type = 'LinuxArmSystem'
     cxx_header = "arch/arm/linux/system.hh"
 
+    @classmethod
+    def export_method_cxx_predecls(cls, code):
+        code('#include "arch/arm/linux/system.hh"')
+
+    @classmethod
+    def export_methods(cls, code):
+        code('''void dumpDmesg();''')
+
 class FreebsdArmSystem(GenericArmSystem):
     type = 'FreebsdArmSystem'
     cxx_header = "arch/arm/freebsd/system.hh"

src/arch/arm/linux/system.cc

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010-2013 ARM Limited
+ * Copyright (c) 2010-2013, 2016 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -53,6 +53,7 @@
 #include "cpu/thread_context.hh"
 #include "debug/Loader.hh"
 #include "kern/linux/events.hh"
+#include "kern/linux/helpers.hh"
 #include "mem/fs_translating_port_proxy.hh"
 #include "mem/physical.hh"
 #include "sim/stat_control.hh"
@@ -65,14 +66,21 @@ LinuxArmSystem::LinuxArmSystem(Params *p)
       enableContextSwitchStatsDump(p->enable_context_switch_stats_dump),
       taskFile(nullptr), kernelPanicEvent(nullptr), kernelOopsEvent(nullptr)
 {
+    const std::string dmesg_output = name() + ".dmesg";
     if (p->panic_on_panic) {
-        kernelPanicEvent = addKernelFuncEventOrPanic<PanicPCEvent>(
-            "panic", "Kernel panic in simulated kernel");
+        kernelPanicEvent = addKernelFuncEventOrPanic<Linux::KernelPanicEvent>(
+            "panic", "Kernel panic in simulated kernel", dmesg_output);
+    } else {
+        kernelPanicEvent = addKernelFuncEventOrPanic<Linux::DmesgDumpEvent>(
+            "panic", "Kernel panic in simulated kernel", dmesg_output);
     }
 
     if (p->panic_on_oops) {
-        kernelOopsEvent = addKernelFuncEventOrPanic<PanicPCEvent>(
-            "oops_exit", "Kernel oops in guest");
+        kernelOopsEvent = addKernelFuncEventOrPanic<Linux::KernelPanicEvent>(
+            "oops_exit", "Kernel oops in guest", dmesg_output);
+    } else {
+        kernelOopsEvent = addKernelFuncEventOrPanic<Linux::DmesgDumpEvent>(
+            "oops_exit", "Kernel oops in guest", dmesg_output);
     }
 
     // With ARM udelay() is #defined to __udelay
@@ -261,6 +269,12 @@ LinuxArmSystem::mapPid(ThreadContext *tc, uint32_t pid)
     }
 }
 
+void
+LinuxArmSystem::dumpDmesg()
+{
+    Linux::dumpDmesg(getThreadContext(0), std::cout);
+}
+
 /** This function is called whenever the the kernel function
  *  "__switch_to" is called to change running tasks.
  *

src/arch/arm/linux/system.hh

@@ -95,6 +95,12 @@ class LinuxArmSystem : public GenericArmSystem
      * @param tc thread context that is currentyl executing  */
     void mapPid(ThreadContext* tc, uint32_t pid);
 
+  public: // Exported Python methods
+    /**
+     * Dump the kernel's dmesg buffer to stdout
+     */
+    void dumpDmesg();
+
   private:
     /** Event to halt the simulator if the kernel calls panic()  */
     PCEvent *kernelPanicEvent;