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//===----- GDBRegistrationListener.cpp - Registers objects with GDB -------===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
#include "llvm-c/ExecutionEngine.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ExecutionEngine/JITEventListener.h"
#include "llvm/Object/ObjectFile.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Mutex.h"
#include <mutex>
using namespace llvm;
using namespace llvm::object;
// This must be kept in sync with gdb/gdb/jit.h .
extern "C" {
typedef enum {
} jit_actions_t;
struct jit_code_entry {
struct jit_code_entry *next_entry;
struct jit_code_entry *prev_entry;
const char *symfile_addr;
uint64_t symfile_size;
struct jit_descriptor {
uint32_t version;
// This should be jit_actions_t, but we want to be specific about the
// bit-width.
uint32_t action_flag;
struct jit_code_entry *relevant_entry;
struct jit_code_entry *first_entry;
// We put information about the JITed function in this global, which the
// debugger reads. Make sure to specify the version statically, because the
// debugger checks the version before we can set it during runtime.
extern struct jit_descriptor __jit_debug_descriptor;
// Debuggers puts a breakpoint in this function.
extern "C" void __jit_debug_register_code();
namespace {
// FIXME: lli aims to provide both, RuntimeDyld and JITLink, as the dynamic
// loaders for it's JIT implementations. And they both offer debugging via the
// GDB JIT interface, which builds on the two well-known symbol names below.
// As these symbols must be unique accross the linked executable, we can only
// define them in one of the libraries and make the other depend on it.
// OrcTargetProcess is a minimal stub for embedding a JIT client in remote
// executors. For the moment it seems reasonable to have the definition there
// and let ExecutionEngine depend on it, until we find a better solution.
LLVM_ATTRIBUTE_USED void requiredSymbolDefinitionsFromOrcTargetProcess() {
errs() << (void *)&__jit_debug_register_code
<< (void *)&__jit_debug_descriptor;
struct RegisteredObjectInfo {
RegisteredObjectInfo() = default;
RegisteredObjectInfo(std::size_t Size, jit_code_entry *Entry,
OwningBinary<ObjectFile> Obj)
: Size(Size), Entry(Entry), Obj(std::move(Obj)) {}
std::size_t Size;
jit_code_entry *Entry;
OwningBinary<ObjectFile> Obj;
// Buffer for an in-memory object file in executable memory
typedef llvm::DenseMap<JITEventListener::ObjectKey, RegisteredObjectInfo>
/// Global access point for the JIT debugging interface designed for use with a
/// singleton toolbox. Handles thread-safe registration and deregistration of
/// object files that are in executable memory managed by the client of this
/// class.
class GDBJITRegistrationListener : public JITEventListener {
/// Lock used to serialize all jit registration events, since they
/// modify global variables.
/// Only a single instance of GDBJITRegistrationListener is ever created,
/// and so the lock can be a member variable of that instance. This ensures
/// destructors are run in the correct order.
sys::Mutex JITDebugLock;
/// A map of in-memory object files that have been registered with the
/// JIT interface.
RegisteredObjectBufferMap ObjectBufferMap;
/// Instantiates the JIT service.
GDBJITRegistrationListener() = default;
/// Unregisters each object that was previously registered and releases all
/// internal resources.
~GDBJITRegistrationListener() override;
static GDBJITRegistrationListener &instance() {
static GDBJITRegistrationListener Instance;
return Instance;
/// Creates an entry in the JIT registry for the buffer @p Object,
/// which must contain an object file in executable memory with any
/// debug information for the debugger.
void notifyObjectLoaded(ObjectKey K, const ObjectFile &Obj,
const RuntimeDyld::LoadedObjectInfo &L) override;
/// Removes the internal registration of @p Object, and
/// frees associated resources.
/// Returns true if @p Object was found in ObjectBufferMap.
void notifyFreeingObject(ObjectKey K) override;
/// Deregister the debug info for the given object file from the debugger
/// and delete any temporary copies. This private method does not remove
/// the function from Map so that it can be called while iterating over Map.
void deregisterObjectInternal(RegisteredObjectBufferMap::iterator I);
/// Do the registration.
void NotifyDebugger(jit_code_entry* JITCodeEntry) {
__jit_debug_descriptor.action_flag = JIT_REGISTER_FN;
// Insert this entry at the head of the list.
JITCodeEntry->prev_entry = nullptr;
jit_code_entry* NextEntry = __jit_debug_descriptor.first_entry;
JITCodeEntry->next_entry = NextEntry;
if (NextEntry) {
NextEntry->prev_entry = JITCodeEntry;
__jit_debug_descriptor.first_entry = JITCodeEntry;
__jit_debug_descriptor.relevant_entry = JITCodeEntry;
GDBJITRegistrationListener::~GDBJITRegistrationListener() {
// Free all registered object files.
std::lock_guard<llvm::sys::Mutex> locked(JITDebugLock);
for (RegisteredObjectBufferMap::iterator I = ObjectBufferMap.begin(),
E = ObjectBufferMap.end();
I != E; ++I) {
// Call the private method that doesn't update the map so our iterator
// doesn't break.
void GDBJITRegistrationListener::notifyObjectLoaded(
ObjectKey K, const ObjectFile &Obj,
const RuntimeDyld::LoadedObjectInfo &L) {
OwningBinary<ObjectFile> DebugObj = L.getObjectForDebug(Obj);
// Bail out if debug objects aren't supported.
if (!DebugObj.getBinary())
const char *Buffer = DebugObj.getBinary()->getMemoryBufferRef().getBufferStart();
size_t Size = DebugObj.getBinary()->getMemoryBufferRef().getBufferSize();
std::lock_guard<llvm::sys::Mutex> locked(JITDebugLock);
assert(!ObjectBufferMap.contains(K) &&
"Second attempt to perform debug registration.");
jit_code_entry* JITCodeEntry = new jit_code_entry();
if (!JITCodeEntry) {
"Allocation failed when registering a JIT entry!\n");
} else {
JITCodeEntry->symfile_addr = Buffer;
JITCodeEntry->symfile_size = Size;
ObjectBufferMap[K] =
RegisteredObjectInfo(Size, JITCodeEntry, std::move(DebugObj));
void GDBJITRegistrationListener::notifyFreeingObject(ObjectKey K) {
std::lock_guard<llvm::sys::Mutex> locked(JITDebugLock);
RegisteredObjectBufferMap::iterator I = ObjectBufferMap.find(K);
if (I != ObjectBufferMap.end()) {
void GDBJITRegistrationListener::deregisterObjectInternal(
RegisteredObjectBufferMap::iterator I) {
jit_code_entry*& JITCodeEntry = I->second.Entry;
// Do the unregistration.
__jit_debug_descriptor.action_flag = JIT_UNREGISTER_FN;
// Remove the jit_code_entry from the linked list.
jit_code_entry* PrevEntry = JITCodeEntry->prev_entry;
jit_code_entry* NextEntry = JITCodeEntry->next_entry;
if (NextEntry) {
NextEntry->prev_entry = PrevEntry;
if (PrevEntry) {
PrevEntry->next_entry = NextEntry;
else {
assert(__jit_debug_descriptor.first_entry == JITCodeEntry);
__jit_debug_descriptor.first_entry = NextEntry;
// Tell the debugger which entry we removed, and unregister the code.
__jit_debug_descriptor.relevant_entry = JITCodeEntry;
delete JITCodeEntry;
JITCodeEntry = nullptr;
} // end namespace
namespace llvm {
JITEventListener* JITEventListener::createGDBRegistrationListener() {
return &GDBJITRegistrationListener::instance();
} // namespace llvm
LLVMJITEventListenerRef LLVMCreateGDBRegistrationListener(void)
return wrap(JITEventListener::createGDBRegistrationListener());