Move StopInfoOverride callback to the new architecture plugin

This creates a new Architecture plugin and moves the stop info override
callback to this place. The motivation for this is to remove complex
dependencies from the ArchSpec class because it is used in a lot of
places that (should) know nothing about Process instances and StopInfo
objects.

I also add a test for the functionality covered by the override
callback.

Differential Revision: https://reviews.llvm.org/D31172

llvm-svn: 316609

4 files changed, 177 insertions, 0 deletions

diff --git a/lldb/source/Plugins/Architecture/Arm/ArchitectureArm.cpp b/lldb/source/Plugins/Architecture/Arm/ArchitectureArm.cpp
new file mode 100644
index 00000000000..219adc5463a
--- /dev/null
+++ b/lldb/source/Plugins/Architecture/Arm/ArchitectureArm.cpp
@@ -0,0 +1,131 @@
+//===-- ArchitectureArm.cpp -------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "Plugins/Architecture/Arm/ArchitectureArm.h"
+#include "Plugins/Process/Utility/ARMDefines.h"
+#include "Plugins/Process/Utility/InstructionUtils.h"
+#include "lldb/Core/ArchSpec.h"
+#include "lldb/Core/PluginManager.h"
+#include "lldb/Target/RegisterContext.h"
+#include "lldb/Target/Thread.h"
+
+using namespace lldb_private;
+using namespace lldb;
+
+ConstString ArchitectureArm::GetPluginNameStatic() {
+  return ConstString("arm");
+}
+
+void ArchitectureArm::Initialize() {
+  PluginManager::RegisterPlugin(GetPluginNameStatic(),
+                                "Arm-specific algorithms",
+                                &ArchitectureArm::Create);
+}
+
+void ArchitectureArm::Terminate() {
+  PluginManager::UnregisterPlugin(&ArchitectureArm::Create);
+}
+
+std::unique_ptr<Architecture> ArchitectureArm::Create(const ArchSpec &arch) {
+  if (arch.GetMachine() != llvm::Triple::arm)
+    return nullptr;
+  return std::unique_ptr<Architecture>(new ArchitectureArm());
+}
+
+ConstString ArchitectureArm::GetPluginName() { return GetPluginNameStatic(); }
+uint32_t ArchitectureArm::GetPluginVersion() { return 1; }
+
+void ArchitectureArm::OverrideStopInfo(Thread &thread) {
+  // We need to check if we are stopped in Thumb mode in a IT instruction
+  // and detect if the condition doesn't pass. If this is the case it means
+  // we won't actually execute this instruction. If this happens we need to
+  // clear the stop reason to no thread plans think we are stopped for a
+  // reason and the plans should keep going.
+  //
+  // We do this because when single stepping many ARM processes, debuggers
+  // often use the BVR/BCR registers that says "stop when the PC is not
+  // equal to its current value". This method of stepping means we can end
+  // up stopping on instructions inside an if/then block that wouldn't get
+  // executed. By fixing this we can stop the debugger from seeming like
+  // you stepped through both the "if" _and_ the "else" clause when source
+  // level stepping because the debugger stops regardless due to the BVR/BCR
+  // triggering a stop.
+  //
+  // It also means we can set breakpoints on instructions inside an an
+  // if/then block and correctly skip them if we use the BKPT instruction.
+  // The ARM and Thumb BKPT instructions are unconditional even when executed
+  // in a Thumb IT block.
+  //
+  // If your debugger inserts software traps in ARM/Thumb code, it will
+  // need to use 16 and 32 bit instruction for 16 and 32 bit thumb
+  // instructions respectively. If your debugger inserts a 16 bit thumb
+  // trap on top of a 32 bit thumb instruction for an opcode that is inside
+  // an if/then, it will change the it/then to conditionally execute your
+  // 16 bit trap and then cause your program to crash if it executes the
+  // trailing 16 bits (the second half of the 32 bit thumb instruction you
+  // partially overwrote).
+
+  RegisterContextSP reg_ctx_sp(thread.GetRegisterContext());
+  if (!reg_ctx_sp)
+    return;
+
+  const uint32_t cpsr = reg_ctx_sp->GetFlags(0);
+  if (cpsr == 0)
+    return;
+
+  // Read the J and T bits to get the ISETSTATE
+  const uint32_t J = Bit32(cpsr, 24);
+  const uint32_t T = Bit32(cpsr, 5);
+  const uint32_t ISETSTATE = J << 1 | T;
+  if (ISETSTATE == 0) {
+// NOTE: I am pretty sure we want to enable the code below
+// that detects when we stop on an instruction in ARM mode
+// that is conditional and the condition doesn't pass. This
+// can happen if you set a breakpoint on an instruction that
+// is conditional. We currently will _always_ stop on the
+// instruction which is bad. You can also run into this while
+// single stepping and you could appear to run code in the "if"
+// and in the "else" clause because it would stop at all of the
+// conditional instructions in both.
+// In such cases, we really don't want to stop at this location.
+// I will check with the lldb-dev list first before I enable this.
+#if 0
+    // ARM mode: check for condition on intsruction
+    const addr_t pc = reg_ctx_sp->GetPC();
+    Status error;
+    // If we fail to read the opcode we will get UINT64_MAX as the
+    // result in "opcode" which we can use to detect if we read a
+    // valid opcode.
+    const uint64_t opcode = thread.GetProcess()->ReadUnsignedIntegerFromMemory(pc, 4, UINT64_MAX, error);
+    if (opcode <= UINT32_MAX)
+    {
+        const uint32_t condition = Bits32((uint32_t)opcode, 31, 28);
+        if (!ARMConditionPassed(condition, cpsr))
+        {
+            // We ARE stopped on an ARM instruction whose condition doesn't
+            // pass so this instruction won't get executed.
+            // Regardless of why it stopped, we need to clear the stop info
+            thread.SetStopInfo (StopInfoSP());
+        }
+    }
+#endif
+  } else if (ISETSTATE == 1) {
+    // Thumb mode
+    const uint32_t ITSTATE = Bits32(cpsr, 15, 10) << 2 | Bits32(cpsr, 26, 25);
+    if (ITSTATE != 0) {
+      const uint32_t condition = Bits32(ITSTATE, 7, 4);
+      if (!ARMConditionPassed(condition, cpsr)) {
+        // We ARE stopped in a Thumb IT instruction on an instruction whose
+        // condition doesn't pass so this instruction won't get executed.
+        // Regardless of why it stopped, we need to clear the stop info
+        thread.SetStopInfo(StopInfoSP());
+      }
+    }
+  }
+}
diff --git a/lldb/source/Plugins/Architecture/Arm/ArchitectureArm.h b/lldb/source/Plugins/Architecture/Arm/ArchitectureArm.h
new file mode 100644
index 00000000000..9ce6c69ef27
--- /dev/null
+++ b/lldb/source/Plugins/Architecture/Arm/ArchitectureArm.h
@@ -0,0 +1,35 @@
+//===-- ArchitectureArm.h ---------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLDB_PLUGIN_ARCHITECTURE_ARM_H
+#define LLDB_PLUGIN_ARCHITECTURE_ARM_H
+
+#include "lldb/Core/Architecture.h"
+
+namespace lldb_private {
+
+class ArchitectureArm : public Architecture {
+public:
+  static ConstString GetPluginNameStatic();
+  static void Initialize();
+  static void Terminate();
+
+  ConstString GetPluginName() override;
+  uint32_t GetPluginVersion() override;
+
+  void OverrideStopInfo(Thread &thread) override;
+
+private:
+  static std::unique_ptr<Architecture> Create(const ArchSpec &arch);
+  ArchitectureArm() = default;
+};
+
+} // namespace lldb_private
+
+#endif // LLDB_PLUGIN_ARCHITECTURE_ARM_H
diff --git a/lldb/source/Plugins/Architecture/Arm/CMakeLists.txt b/lldb/source/Plugins/Architecture/Arm/CMakeLists.txt
new file mode 100644
index 00000000000..b9de3bd8903
--- /dev/null
+++ b/lldb/source/Plugins/Architecture/Arm/CMakeLists.txt
@@ -0,0 +1,10 @@
+add_lldb_library(lldbPluginArchitectureArm PLUGIN
+  ArchitectureArm.cpp
+
+  LINK_LIBS
+    lldbPluginProcessUtility
+    lldbCore
+    lldbTarget
+  LINK_COMPONENTS
+    Support
+  )
diff --git a/lldb/source/Plugins/Architecture/CMakeLists.txt b/lldb/source/Plugins/Architecture/CMakeLists.txt
new file mode 100644
index 00000000000..5abaa8e6823
--- /dev/null
+++ b/lldb/source/Plugins/Architecture/CMakeLists.txt
@@ -0,0 +1 @@
+add_subdirectory(Arm)