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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this file,
#ifndef ElfLoader_h
#define ElfLoader_h
#include <vector>
#include <dlfcn.h>
#include <signal.h>
#include "mozilla/Atomics.h"
#include "mozilla/RefCounted.h"
#include "mozilla/RefPtr.h"
#include "mozilla/UniquePtr.h"
#include "Elfxx.h"
#include "Mappable.h"
/**
* dlfcn.h replacement functions
*/
extern "C" {
void* __wrap_dlopen(const char* path, int flags);
const char* __wrap_dlerror(void);
void* __wrap_dlsym(void* handle, const char* symbol);
int __wrap_dlclose(void* handle);
#ifndef HAVE_DLADDR
typedef struct {
const char* dli_fname;
void* dli_fbase;
const char* dli_sname;
void* dli_saddr;
} Dl_info;
#endif
int __wrap_dladdr(const void* addr, Dl_info* info);
typedef int (*dl_phdr_cb)(struct dl_phdr_info*, size_t, void*);
int __wrap_dl_iterate_phdr(dl_phdr_cb callback, void* data);
#ifdef __ARM_EABI__
const void* __wrap___gnu_Unwind_Find_exidx(void* pc, int* pcount);
#endif
}
/* Forward declarations for use in LibHandle */
class BaseElf;
class CustomElf;
class SystemElf;
/**
* Specialize RefCounted template for LibHandle. We may get references to
* LibHandles during the execution of their destructor, so we need
* RefCounted<LibHandle>::Release to support some reentrancy. See further
* below.
*/
class LibHandle;
namespace mozilla {
namespace detail {
template <>
inline void RefCounted<LibHandle, AtomicRefCount>::Release() const;
#ifdef DEBUG
template <>
inline RefCounted<LibHandle, AtomicRefCount>::~RefCounted() {
MOZ_ASSERT(mRefCnt == 0x7fffdead);
}
#endif
} /* namespace detail */
} /* namespace mozilla */
/**
* Abstract class for loaded libraries. Libraries may be loaded through the
* system linker or this linker, both cases will be derived from this class.
*/
class LibHandle : public mozilla::external::AtomicRefCounted<LibHandle> {
public:
MOZ_DECLARE_REFCOUNTED_TYPENAME(LibHandle)
/**
* Constructor. Takes the path of the loaded library and will store a copy
* of the leaf name.
*/
LibHandle(const char* path)
: directRefCnt(0),
path(path ? strdup(path) : nullptr),
mappable(nullptr) {}
/**
* Destructor.
*/
virtual ~LibHandle();
/**
* Returns the pointer to the address to which the given symbol resolves
* inside the library. It is not supposed to resolve the symbol in other
* libraries, although in practice, it will for system libraries.
*/
virtual void* GetSymbolPtr(const char* symbol) const = 0;
/**
* Returns whether the given address is part of the virtual address space
* covered by the loaded library.
*/
virtual bool Contains(void* addr) const = 0;
/**
* Returns the base address of the loaded library.
*/
virtual void* GetBase() const = 0;
/**
* Returns the file name of the library without the containing directory.
*/
const char* GetName() const;
/**
* Returns the full path of the library, when available. Otherwise, returns
* the file name.
*/
const char* GetPath() const { return path; }
/**
* Library handles can be referenced from other library handles or
* externally (when dlopen()ing using this linker). We need to be
* able to distinguish between the two kind of referencing for better
* bookkeeping.
*/
void AddDirectRef() {
mozilla::external::AtomicRefCounted<LibHandle>::AddRef();
++directRefCnt;
}
/**
* Releases a direct reference, and returns whether there are any direct
* references left.
*/
bool ReleaseDirectRef() {
const MozRefCountType count = --directRefCnt;
MOZ_ASSERT(count + 1 > 0);
MOZ_ASSERT(count + 1 <=
mozilla::external::AtomicRefCounted<LibHandle>::refCount());
mozilla::external::AtomicRefCounted<LibHandle>::Release();
return !!count;
}
/**
* Returns the number of direct references
*/
MozRefCountType DirectRefCount() { return directRefCnt; }
#ifdef __ARM_EABI__
/**
* Find the address and entry count of the ARM.exidx section
* associated with the library
*/
virtual const void* FindExidx(int* pcount) const = 0;
#endif
protected:
/**
* Returns the instance, casted as the wanted type. Returns nullptr if
* that's not the actual type. (short of a better way to do this without
* RTTI)
*/
friend class ElfLoader;
friend class CustomElf;
friend class SEGVHandler;
friend int __wrap_dl_iterate_phdr(dl_phdr_cb callback, void* data);
virtual BaseElf* AsBaseElf() { return nullptr; }
virtual SystemElf* AsSystemElf() { return nullptr; }
private:
mozilla::Atomic<MozRefCountType> directRefCnt;
char* path;
/* Mappable object keeping the result of GetMappable() */
mutable RefPtr<Mappable> mappable;
};
/**
* Specialized RefCounted<LibHandle>::Release. Under normal operation, when
* mRefCnt reaches 0, the LibHandle is deleted. Its mRefCnt is however
* increased to 1 on normal builds, and 0x7fffdead on debug builds so that the
* LibHandle can still be referenced while the destructor is executing. The
* mRefCnt is allowed to grow > 0x7fffdead, but not to decrease under that
* value, which would mean too many Releases from within the destructor.
*/
namespace mozilla {
namespace detail {
template <>
inline void RefCounted<LibHandle, AtomicRefCount>::Release() const {
#ifdef DEBUG
if (mRefCnt > 0x7fff0000) MOZ_ASSERT(mRefCnt > 0x7fffdead);
#endif
MOZ_ASSERT(mRefCnt > 0);
if (mRefCnt > 0) {
if (0 == --mRefCnt) {
#ifdef DEBUG
mRefCnt = 0x7fffdead;
#else
++mRefCnt;
#endif
delete static_cast<const LibHandle*>(this);
}
}
}
} /* namespace detail */
} /* namespace mozilla */
/**
* Class handling libraries loaded by the system linker
*/
class SystemElf : public LibHandle {
public:
/**
* Returns a new SystemElf for the given path. The given flags are passed
* to dlopen().
*/
static already_AddRefed<LibHandle> Load(const char* path, int flags);
/**
* Inherited from LibHandle
*/
virtual ~SystemElf();
virtual void* GetSymbolPtr(const char* symbol) const;
virtual bool Contains(void* addr) const { return false; /* UNIMPLEMENTED */ }
virtual void* GetBase() const { return nullptr; /* UNIMPLEMENTED */ }
#ifdef __ARM_EABI__
virtual const void* FindExidx(int* pcount) const;
#endif
protected:
/**
* Returns the instance, casted as SystemElf. (short of a better way to do
* this without RTTI)
*/
friend class ElfLoader;
virtual SystemElf* AsSystemElf() { return this; }
/**
* Remove the reference to the system linker handle. This avoids dlclose()
* being called when the instance is destroyed.
*/
void Forget() { dlhandle = nullptr; }
private:
/**
* Private constructor
*/
SystemElf(const char* path, void* handle)
: LibHandle(path), dlhandle(handle) {}
/* Handle as returned by system dlopen() */
void* dlhandle;
};
/**
* The ElfLoader registers its own SIGSEGV handler to handle segmentation
* faults within the address space of the loaded libraries. It however
* allows a handler to be set for faults in other places, and redispatches
* to the handler set through signal() or sigaction().
*/
class SEGVHandler {
public:
bool hasRegisteredHandler() {
if (!initialized) FinishInitialization();
return registeredHandler;
}
static int __wrap_sigaction(int signum, const struct sigaction* act,
struct sigaction* oldact);
protected:
SEGVHandler();
~SEGVHandler();
private:
/**
* The constructor doesn't do all initialization, and the tail is done
* at a later time.
*/
void FinishInitialization();
/**
* SIGSEGV handler registered with __wrap_signal or __wrap_sigaction.
*/
struct sigaction action;
/**
* ElfLoader SIGSEGV handler.
*/
static void handler(int signum, siginfo_t* info, void* context);
/**
* Temporary test handler.
*/
static void test_handler(int signum, siginfo_t* info, void* context);
/**
* Size of the alternative stack. The printf family requires more than 8KB
* of stack, and our signal handler may print a few things.
*/
static const size_t stackSize = 12 * 1024;
/**
* Alternative stack information used before initialization.
*/
stack_t oldStack;
/**
* Pointer to an alternative stack for signals. Only set if oldStack is
* not set or not big enough.
*/
MappedPtr stackPtr;
bool initialized;
bool registeredHandler;
bool signalHandlingSlow;
};
/**
* Elf Loader class in charge of loading and bookkeeping libraries.
*/
class ElfLoader : public SEGVHandler {
public:
/**
* The Elf Loader instance
*/
static ElfLoader Singleton;
/**
* Loads the given library with the given flags. Equivalent to dlopen()
* The extra "parent" argument optionally gives the handle of the library
* requesting the given library to be loaded. The loader may look in the
* directory containing that parent library for the library to load.
*/
already_AddRefed<LibHandle> Load(const char* path, int flags,
LibHandle* parent = nullptr);
/**
* Returns the handle of the library containing the given address in
* its virtual address space, i.e. the library handle for which
* LibHandle::Contains returns true. Its purpose is to allow to
* implement dladdr().
*/
already_AddRefed<LibHandle> GetHandleByPtr(void* addr);
/**
* Returns a Mappable object for the path. Paths in the form
* /foo/bar/baz/archive!/directory/lib.so
* try to load the directory/lib.so in /foo/bar/baz/archive, provided
* that file is a Zip archive.
*/
static Mappable* GetMappableFromPath(const char* path);
void ExpectShutdown(bool val) { expect_shutdown = val; }
bool IsShutdownExpected() { return expect_shutdown; }
private:
bool expect_shutdown;
protected:
/**
* Registers the given handle. This method is meant to be called by
* LibHandle subclass creators.
*/
void Register(LibHandle* handle);
void Register(CustomElf* handle);
/**
* Forget about the given handle. This method is meant to be called by
* LibHandle subclass destructors.
*/
void Forget(LibHandle* handle);
void Forget(CustomElf* handle);
friend class SystemElf;
friend const char* __wrap_dlerror(void);
friend void* __wrap_dlsym(void* handle, const char* symbol);
friend int __wrap_dlclose(void* handle);
/* __wrap_dlerror() returns this custom last error if non-null or the system
* dlerror() value if this is null. Must refer to a string constant. */
mozilla::Atomic<const char*, mozilla::Relaxed> lastError;
private:
ElfLoader() : expect_shutdown(true), lastError(nullptr) {
pthread_mutex_init(&handlesMutex, nullptr);
}
~ElfLoader();
/* Initialization code that can't run during static initialization. */
void Init();
/* System loader handle for the library/program containing our code. This
* is used to resolve wrapped functions. */
RefPtr<LibHandle> self_elf;
/* Bookkeeping */
typedef std::vector<LibHandle*> LibHandleList;
LibHandleList handles;
pthread_mutex_t handlesMutex;
protected:
friend class CustomElf;
friend class LoadedElf;
/* Definition of static destructors as to be used for C++ ABI compatibility */
typedef void (*Destructor)(void* object);
/**
* C++ ABI makes static initializers register destructors through a specific
* atexit interface. On glibc/linux systems, the dso_handle is a pointer
* within a given library. On bionic/android systems, it is an undefined
* symbol. Making sense of the value is not really important, and all that
* is really important is that it is different for each loaded library, so
* that they can be discriminated when shutting down. For convenience, on
* systems where the dso handle is a symbol, that symbol is resolved to
* point at corresponding CustomElf.
*
* Destructors are registered with __*_atexit with an associated object to
* be passed as argument when it is called.
*
* When __cxa_finalize is called, destructors registered for the given
* DSO handle are called in the reverse order they were registered.
*/
#ifdef __ARM_EABI__
static int __wrap_aeabi_atexit(void* that, Destructor destructor,
void* dso_handle);
#else
static int __wrap_cxa_atexit(Destructor destructor, void* that,
void* dso_handle);
#endif
static void __wrap_cxa_finalize(void* dso_handle);
/**
* Registered destructor. Keeps track of the destructor function pointer,
* associated object to call it with, and DSO handle.
*/
class DestructorCaller {
public:
DestructorCaller(Destructor destructor, void* object, void* dso_handle)
: destructor(destructor), object(object), dso_handle(dso_handle) {}
/**
* Call the destructor function with the associated object.
* Call only once, see CustomElf::~CustomElf.
*/
void Call();
/**
* Returns whether the destructor is associated to the given DSO handle
*/
bool IsForHandle(void* handle) const { return handle == dso_handle; }
private:
Destructor destructor;
void* object;
void* dso_handle;
};
private:
/* Keep track of all registered destructors */
std::vector<DestructorCaller> destructors;
/* Forward declaration, see further below */
class DebuggerHelper;
public:
/* Loaded object descriptor for the debugger interface below*/
struct link_map {
/* Base address of the loaded object. */
const void* l_addr;
/* File name */
const char* l_name;
/* Address of the PT_DYNAMIC segment. */
const void* l_ld;
private:
friend class ElfLoader::DebuggerHelper;
/* Double linked list of loaded objects. */
link_map *l_next, *l_prev;
};
private:
/* Data structure used by the linker to give details about shared objects it
* loaded to debuggers. This is normally defined in link.h, but Android
* headers lack this file. */
struct r_debug {
/* Version number of the protocol. */
int r_version;
/* Head of the linked list of loaded objects. */
link_map* r_map;
/* Function to be called when updates to the linked list of loaded objects
* are going to occur. The function is to be called before and after
* changes. */
void (*r_brk)(void);
/* Indicates to the debugger what state the linked list of loaded objects
* is in when the function above is called. */
enum {
RT_CONSISTENT, /* Changes are complete */
RT_ADD, /* Beginning to add a new object */
RT_DELETE /* Beginning to remove an object */
} r_state;
};
/* Memory representation of ELF Auxiliary Vectors */
struct AuxVector {
Elf::Addr type;
Elf::Addr value;
};
/* Helper class used to integrate libraries loaded by this linker in
* r_debug */
class DebuggerHelper {
public:
DebuggerHelper();
void Init(AuxVector* auvx);
explicit operator bool() { return dbg; }
/* Make the debugger aware of a new loaded object */
void Add(link_map* map);
/* Make the debugger aware of the unloading of an object */
void Remove(link_map* map);
/* Iterates over all link_maps */
class iterator {
public:
const link_map* operator->() const { return item; }
const link_map& operator++() {
item = item->l_next;
return *item;
}
bool operator<(const iterator& other) const {
if (other.item == nullptr) return item ? true : false;
MOZ_CRASH(
"DebuggerHelper::iterator::operator< called with something else "
"than DebuggerHelper::end()");
}
protected:
friend class DebuggerHelper;
explicit iterator(const link_map* item) : item(item) {}
private:
const link_map* item;
};
iterator begin() const { return iterator(dbg ? dbg->r_map : nullptr); }
iterator end() const { return iterator(nullptr); }
private:
r_debug* dbg;
link_map* firstAdded;
};
friend int __wrap_dl_iterate_phdr(dl_phdr_cb callback, void* data);
DebuggerHelper dbg;
};
#endif /* ElfLoader_h */