1//===----- GDBRegistrationListener.cpp - Registers objects with GDB -------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#include "llvm-c/ExecutionEngine.h"
10#include "llvm/ADT/DenseMap.h"
11#include "llvm/ExecutionEngine/JITEventListener.h"
12#include "llvm/Object/ObjectFile.h"
13#include "llvm/Support/Compiler.h"
14#include "llvm/Support/ErrorHandling.h"
15#include "llvm/Support/ManagedStatic.h"
16#include "llvm/Support/Mutex.h"
17#include <mutex>
18
19using namespace llvm;
20using namespace llvm::object;
21
22// This must be kept in sync with gdb/gdb/jit.h .
23extern "C" {
24
25  typedef enum {
26    JIT_NOACTION = 0,
27    JIT_REGISTER_FN,
28    JIT_UNREGISTER_FN
29  } jit_actions_t;
30
31  struct jit_code_entry {
32    struct jit_code_entry *next_entry;
33    struct jit_code_entry *prev_entry;
34    const char *symfile_addr;
35    uint64_t symfile_size;
36  };
37
38  struct jit_descriptor {
39    uint32_t version;
40    // This should be jit_actions_t, but we want to be specific about the
41    // bit-width.
42    uint32_t action_flag;
43    struct jit_code_entry *relevant_entry;
44    struct jit_code_entry *first_entry;
45  };
46
47  // We put information about the JITed function in this global, which the
48  // debugger reads.  Make sure to specify the version statically, because the
49  // debugger checks the version before we can set it during runtime.
50  struct jit_descriptor __jit_debug_descriptor = { 1, 0, nullptr, nullptr };
51
52  // Debuggers puts a breakpoint in this function.
53  LLVM_ATTRIBUTE_NOINLINE void __jit_debug_register_code() {
54    // The noinline and the asm prevent calls to this function from being
55    // optimized out.
56#if !defined(_MSC_VER)
57    asm volatile("":::"memory");
58#endif
59  }
60
61}
62
63namespace {
64
65struct RegisteredObjectInfo {
66  RegisteredObjectInfo() {}
67
68  RegisteredObjectInfo(std::size_t Size, jit_code_entry *Entry,
69                       OwningBinary<ObjectFile> Obj)
70    : Size(Size), Entry(Entry), Obj(std::move(Obj)) {}
71
72  std::size_t Size;
73  jit_code_entry *Entry;
74  OwningBinary<ObjectFile> Obj;
75};
76
77// Buffer for an in-memory object file in executable memory
78typedef llvm::DenseMap<JITEventListener::ObjectKey, RegisteredObjectInfo>
79    RegisteredObjectBufferMap;
80
81/// Global access point for the JIT debugging interface designed for use with a
82/// singleton toolbox. Handles thread-safe registration and deregistration of
83/// object files that are in executable memory managed by the client of this
84/// class.
85class GDBJITRegistrationListener : public JITEventListener {
86  /// A map of in-memory object files that have been registered with the
87  /// JIT interface.
88  RegisteredObjectBufferMap ObjectBufferMap;
89
90public:
91  /// Instantiates the JIT service.
92  GDBJITRegistrationListener() : ObjectBufferMap() {}
93
94  /// Unregisters each object that was previously registered and releases all
95  /// internal resources.
96  ~GDBJITRegistrationListener() override;
97
98  /// Creates an entry in the JIT registry for the buffer @p Object,
99  /// which must contain an object file in executable memory with any
100  /// debug information for the debugger.
101  void notifyObjectLoaded(ObjectKey K, const ObjectFile &Obj,
102                          const RuntimeDyld::LoadedObjectInfo &L) override;
103
104  /// Removes the internal registration of @p Object, and
105  /// frees associated resources.
106  /// Returns true if @p Object was found in ObjectBufferMap.
107  void notifyFreeingObject(ObjectKey K) override;
108
109private:
110  /// Deregister the debug info for the given object file from the debugger
111  /// and delete any temporary copies.  This private method does not remove
112  /// the function from Map so that it can be called while iterating over Map.
113  void deregisterObjectInternal(RegisteredObjectBufferMap::iterator I);
114};
115
116/// Lock used to serialize all jit registration events, since they
117/// modify global variables.
118ManagedStatic<sys::Mutex> JITDebugLock;
119
120/// Do the registration.
121void NotifyDebugger(jit_code_entry* JITCodeEntry) {
122  __jit_debug_descriptor.action_flag = JIT_REGISTER_FN;
123
124  // Insert this entry at the head of the list.
125  JITCodeEntry->prev_entry = nullptr;
126  jit_code_entry* NextEntry = __jit_debug_descriptor.first_entry;
127  JITCodeEntry->next_entry = NextEntry;
128  if (NextEntry) {
129    NextEntry->prev_entry = JITCodeEntry;
130  }
131  __jit_debug_descriptor.first_entry = JITCodeEntry;
132  __jit_debug_descriptor.relevant_entry = JITCodeEntry;
133  __jit_debug_register_code();
134}
135
136GDBJITRegistrationListener::~GDBJITRegistrationListener() {
137  // Free all registered object files.
138  std::lock_guard<llvm::sys::Mutex> locked(*JITDebugLock);
139  for (RegisteredObjectBufferMap::iterator I = ObjectBufferMap.begin(),
140                                           E = ObjectBufferMap.end();
141       I != E; ++I) {
142    // Call the private method that doesn't update the map so our iterator
143    // doesn't break.
144    deregisterObjectInternal(I);
145  }
146  ObjectBufferMap.clear();
147}
148
149void GDBJITRegistrationListener::notifyObjectLoaded(
150    ObjectKey K, const ObjectFile &Obj,
151    const RuntimeDyld::LoadedObjectInfo &L) {
152
153  OwningBinary<ObjectFile> DebugObj = L.getObjectForDebug(Obj);
154
155  // Bail out if debug objects aren't supported.
156  if (!DebugObj.getBinary())
157    return;
158
159  const char *Buffer = DebugObj.getBinary()->getMemoryBufferRef().getBufferStart();
160  size_t      Size = DebugObj.getBinary()->getMemoryBufferRef().getBufferSize();
161
162  std::lock_guard<llvm::sys::Mutex> locked(*JITDebugLock);
163  assert(ObjectBufferMap.find(K) == ObjectBufferMap.end() &&
164         "Second attempt to perform debug registration.");
165  jit_code_entry* JITCodeEntry = new jit_code_entry();
166
167  if (!JITCodeEntry) {
168    llvm::report_fatal_error(
169      "Allocation failed when registering a JIT entry!\n");
170  } else {
171    JITCodeEntry->symfile_addr = Buffer;
172    JITCodeEntry->symfile_size = Size;
173
174    ObjectBufferMap[K] =
175        RegisteredObjectInfo(Size, JITCodeEntry, std::move(DebugObj));
176    NotifyDebugger(JITCodeEntry);
177  }
178}
179
180void GDBJITRegistrationListener::notifyFreeingObject(ObjectKey K) {
181  std::lock_guard<llvm::sys::Mutex> locked(*JITDebugLock);
182  RegisteredObjectBufferMap::iterator I = ObjectBufferMap.find(K);
183
184  if (I != ObjectBufferMap.end()) {
185    deregisterObjectInternal(I);
186    ObjectBufferMap.erase(I);
187  }
188}
189
190void GDBJITRegistrationListener::deregisterObjectInternal(
191    RegisteredObjectBufferMap::iterator I) {
192
193  jit_code_entry*& JITCodeEntry = I->second.Entry;
194
195  // Do the unregistration.
196  {
197    __jit_debug_descriptor.action_flag = JIT_UNREGISTER_FN;
198
199    // Remove the jit_code_entry from the linked list.
200    jit_code_entry* PrevEntry = JITCodeEntry->prev_entry;
201    jit_code_entry* NextEntry = JITCodeEntry->next_entry;
202
203    if (NextEntry) {
204      NextEntry->prev_entry = PrevEntry;
205    }
206    if (PrevEntry) {
207      PrevEntry->next_entry = NextEntry;
208    }
209    else {
210      assert(__jit_debug_descriptor.first_entry == JITCodeEntry);
211      __jit_debug_descriptor.first_entry = NextEntry;
212    }
213
214    // Tell the debugger which entry we removed, and unregister the code.
215    __jit_debug_descriptor.relevant_entry = JITCodeEntry;
216    __jit_debug_register_code();
217  }
218
219  delete JITCodeEntry;
220  JITCodeEntry = nullptr;
221}
222
223llvm::ManagedStatic<GDBJITRegistrationListener> GDBRegListener;
224
225} // end namespace
226
227namespace llvm {
228
229JITEventListener* JITEventListener::createGDBRegistrationListener() {
230  return &*GDBRegListener;
231}
232
233} // namespace llvm
234
235LLVMJITEventListenerRef LLVMCreateGDBRegistrationListener(void)
236{
237  return wrap(JITEventListener::createGDBRegistrationListener());
238}
239