[lldb] [Process/FreeBSDKernel] Introduce libkvm support

[mgorny]

Summary

Introduce initial support for using libkvm on FreeBSD. The library
can be used as an alternate implementation for processing kernel
coredumps but it can also be used to access live kernel memory through
specifying "/dev/mem" as the core file, i.e.:

lldb --core /dev/mem /boot/kernel/kernel

[labath]

How about factoring the two implementations into subclasses. If the classes are small, maybe you can just declare them in the cpp file...

[mgorny]

Split into FVC/KVM classes.

[mgorny]

In D116005#3202721, @labath wrote:

How about factoring the two implementations into subclasses. If the classes are small, maybe you can just declare them in the cpp file...

Yes, that's a nice idea. As an extra, we can easily use the real pointer types and remove all these casts.

[labath]

Just a couple of quick comments.

In D116005#3203077, @mgorny wrote:

In D116005#3202721, @labath wrote:

How about factoring the two implementations into subclasses. If the classes are small, maybe you can just declare them in the cpp file...

Yes, that's a nice idea. As an extra, we can easily use the real pointer types and remove all these casts.

Yep. :)

lldb/source/Plugins/Process/FreeBSDKernel/ProcessFreeBSDKernel.cpp

31–52

put into anonymous namespace, for maximum compliance.

71

Do you really want to do this if the fvc call was successful? What is the expected priority of the two implementations? Maybe just use return statements instead of assignments?

74

is looks like this ought to be private

[mgorny]

lldb/source/Plugins/Process/FreeBSDKernel/ProcessFreeBSDKernel.cpp

71

Oh shi, I didn't notice that it doesn't use return statements. Fixed now.

[mgorny]

Implemented requested changed.

lldb/source/Plugins/Process/FreeBSDKernel/CMakeLists.txt

-if (NOT FBSDVMCore_FOUND)
+set(FBSDKERNEL_LIBS)
+if(FBSDVMCore_FOUND)
+  list(APPEND FBSDKERNEL_LIBS fbsdvmcore)
+endif()
+if(${CMAKE_SYSTEM_NAME} MATCHES "FreeBSD")
+  list(APPEND FBSDKERNEL_LIBS kvm)
+endif()
+
+if (NOT FBSDKERNEL_LIBS)
   message(STATUS "Skipping FreeBSDKernel plugin due to missing libfbsdvmcore")
   return()
 endif()
 
 add_lldb_library(lldbPluginProcessFreeBSDKernel PLUGIN
   ProcessFreeBSDKernel.cpp
   RegisterContextFreeBSDKernel_arm64.cpp
   RegisterContextFreeBSDKernel_i386.cpp
   RegisterContextFreeBSDKernel_x86_64.cpp
   ThreadFreeBSDKernel.cpp
 
   LINK_LIBS
     lldbCore
     lldbTarget
-    fbsdvmcore
+    ${FBSDKERNEL_LIBS}
   LINK_COMPONENTS
     Support
   )

lldb/source/Plugins/Process/FreeBSDKernel/ProcessFreeBSDKernel.h

 //===-- ProcessFreeBSDKernel.h ----------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLDB_SOURCE_PLUGINS_PROCESS_FREEBSDKERNEL_PROCESSFREEBSDKERNEL_H
 #define LLDB_SOURCE_PLUGINS_PROCESS_FREEBSDKERNEL_PROCESSFREEBSDKERNEL_H
 
 #include "lldb/Target/PostMortemProcess.h"
 
 class ProcessFreeBSDKernel : public lldb_private::PostMortemProcess {
 public:
+  enum class CoreProvider {
+#if LLDB_ENABLE_FBSDVMCORE
+    fvc,
+#endif
+#if defined(__FreeBSD__)
+    kvm,
+#endif
+  };
+
   ProcessFreeBSDKernel(lldb::TargetSP target_sp, lldb::ListenerSP listener,
-                       const lldb_private::FileSpec &core_file, void *fvc);
+                       const lldb_private::FileSpec &core_file, void *fvc,
+                       CoreProvider core_provider);
 
   ~ProcessFreeBSDKernel() override;
 
   static lldb::ProcessSP
   CreateInstance(lldb::TargetSP target_sp, lldb::ListenerSP listener,
                  const lldb_private::FileSpec *crash_file_path,
                  bool can_connect);
 
#endif
   lldb_private::DynamicLoader *GetDynamicLoader() override;
 
 protected:
   bool DoUpdateThreadList(lldb_private::ThreadList &old_thread_list,
                           lldb_private::ThreadList &new_thread_list) override;
 
 private:
   void *m_fvc;
+  CoreProvider m_core_provider;
+
+  const char *GetError();
 };
 
 #endif // LLDB_SOURCE_PLUGINS_PROCESS_FREEBSDKERNEL_PROCESSFREEBSDKERNEL_H

lldb/source/Plugins/Process/FreeBSDKernel/ProcessFreeBSDKernel.cpp

 //===-- ProcessFreeBSDKernel.cpp ------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "lldb/Core/Module.h"
 #include "lldb/Core/PluginManager.h"
 #include "lldb/Target/DynamicLoader.h"
 
+#include "Plugins/DynamicLoader/Static/DynamicLoaderStatic.h"
 #include "ProcessFreeBSDKernel.h"
 #include "ThreadFreeBSDKernel.h"
-#include "Plugins/DynamicLoader/Static/DynamicLoaderStatic.h"
 
+#if LLDB_ENABLE_FBSDVMCORE
 #include <fvc.h>
+#endif
+#if defined(__FreeBSD__)
+#include <kvm.h>
+#endif
 
 using namespace lldb;
 using namespace lldb_private;
 
 LLDB_PLUGIN_DEFINE(ProcessFreeBSDKernel)
 
 ProcessFreeBSDKernel::ProcessFreeBSDKernel(lldb::TargetSP target_sp,
                                            ListenerSP listener_sp,
-                                           const FileSpec &core_file, void *fvc)
-    : PostMortemProcess(target_sp, listener_sp), m_fvc(fvc) {}
+                                           const FileSpec &core_file, void *fvc,
+                                           CoreProvider core_provider)
+    : PostMortemProcess(target_sp, listener_sp), m_fvc(fvc),
+      m_core_provider(core_provider) {}
 
 ProcessFreeBSDKernel::~ProcessFreeBSDKernel() {
-  if (m_fvc)
+  if (m_fvc) {
+    switch (m_core_provider) {
+#if LLDB_ENABLE_FBSDVMCORE
+    case CoreProvider::fvc:
       fvc_close(static_cast<fvc_t *>(m_fvc));
+      break;
+#endif
+#if defined(__FreeBSD__)
+    case CoreProvider::kvm:
+      kvm_close(static_cast<kvm_t *>(m_fvc));
+      break;
+#endif
+    }
+  }
 }
 
 lldb::ProcessSP ProcessFreeBSDKernel::CreateInstance(lldb::TargetSP target_sp,
                                                      ListenerSP listener_sp,
                                                      const FileSpec *crash_file,
                                                      bool can_connect) {
   lldb::ProcessSP process_sp;
   ModuleSP executable = target_sp->GetExecutableModule();
   if (crash_file && !can_connect && executable) {
-    fvc_t *fvc = fvc_open(
-        executable->GetFileSpec().GetPath().c_str(),
+#if LLDB_ENABLE_FBSDVMCORE
+    fvc_t *fvc =
+        fvc_open(executable->GetFileSpec().GetPath().c_str(),
                  crash_file->GetPath().c_str(), nullptr, nullptr, nullptr);
     if (fvc)
       process_sp = std::make_shared<ProcessFreeBSDKernel>(
-          target_sp, listener_sp, *crash_file, fvc);
+          target_sp, listener_sp, *crash_file, fvc, CoreProvider::fvc);
+#endif
+
+#if defined(__FreeBSD__)
+    kvm_t *kvm =
+        kvm_open2(executable->GetFileSpec().GetPath().c_str(),
+                  crash_file->GetPath().c_str(), O_RDONLY, nullptr, nullptr);
+    if (kvm)
+      process_sp = std::make_shared<ProcessFreeBSDKernel>(
+          target_sp, listener_sp, *crash_file, kvm, CoreProvider::kvm);
+#endif
   }
   return process_sp;
 }
 
 void ProcessFreeBSDKernel::Initialize() {
   static llvm::once_flag g_once_flag;
 
   llvm::call_once(g_once_flag, []() {

 
 Status ProcessFreeBSDKernel::DoLoadCore() {
   // The core is already loaded by CreateInstance().
   return Status();
 }
 
 size_t ProcessFreeBSDKernel::DoReadMemory(lldb::addr_t addr, void *buf,
                                           size_t size, Status &error) {
-  ssize_t rd = fvc_read(static_cast<fvc_t *>(m_fvc), addr, buf, size);
+  ssize_t rd = 0;
+  switch (m_core_provider) {
+#if LLDB_ENABLE_FBSDVMCORE
+  case CoreProvider::fvc:
+    rd = fvc_read(static_cast<fvc_t *>(m_fvc), addr, buf, size);
+    break;
+#endif
+#if defined(__FreeBSD__)
+  case CoreProvider::kvm:
+    rd = kvm_read2(static_cast<kvm_t *>(m_fvc), addr, buf, size);
+    break;
+#endif
+  }
   if (rd < 0 || static_cast<size_t>(rd) != size) {
-    error.SetErrorStringWithFormat("Reading memory failed: %s",
-                                   fvc_geterr(static_cast<fvc_t *>(m_fvc)));
+    error.SetErrorStringWithFormat("Reading memory failed: %s", GetError());
     return rd > 0 ? rd : 0;
   }
   return rd;
 }
 
 DynamicLoader *ProcessFreeBSDKernel::GetDynamicLoader() {
   if (m_dyld_up.get() == nullptr)
     m_dyld_up.reset(DynamicLoader::FindPlugin(
         this, DynamicLoaderStatic::GetPluginNameStatic()));
   return m_dyld_up.get();
 }
+
+const char *ProcessFreeBSDKernel::GetError() {
+  switch (m_core_provider) {
+#if LLDB_ENABLE_FBSDVMCORE
+  case CoreProvider::fvc:
+    return fvc_geterr(static_cast<fvc_t *>(m_fvc));
+#endif
+#if defined(__FreeBSD__)
+  case CoreProvider::kvm:
+    return kvm_geterr(static_cast<kvm_t *>(m_fvc));
+#endif
+  }
+}

lldb/test/API/functionalities/postmortem/FreeBSDKernel/TestFreeBSDKernelLive.py

+import os
+import struct
+import subprocess
+
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class FreeBSDKernelVMCoreTestCase(TestBase):
+    NO_DEBUG_INFO_TESTCASE = True
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    def test_mem(self):
+        kernel_exec = "/boot/kernel/kernel"
+        mem_device = "/dev/mem"
+
+        if not os.access(kernel_exec, os.R_OK):
+            self.skipTest("Kernel @ %s is not readable" % (kernel_exec,))
+        if not os.access(mem_device, os.R_OK):
+            self.skipTest("Memory @ %s is not readable" % (mem_device,))
+
+        target = self.dbg.CreateTarget(kernel_exec)
+        process = target.LoadCore(mem_device)
+        hz_value = int(subprocess.check_output(["sysctl", "-n", "kern.hz"]))
+
+        self.assertTrue(process, PROCESS_IS_VALID)
+        self.assertEqual(process.GetNumThreads(), 1)
+        self.assertEqual(process.GetProcessID(), 0)
+
+        # test memory reading
+        self.expect("expr -- *(int *) &hz",
+                    substrs=["(int) $0 = %d" % hz_value])
+
+        main_mod = target.GetModuleAtIndex(0)
+        hz_addr = (main_mod.FindSymbols("hz")[0].symbol.addr
+                   .GetLoadAddress(target))
+        error = lldb.SBError()
+        self.assertEqual(process.ReadMemory(hz_addr, 4, error),
+                         struct.pack("<I", hz_value))
+
+        self.dbg.DeleteTarget(target)