gecko-dev/mozglue/linker/ElfLoader.h

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C++

/* 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,
* You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef ElfLoader_h
#define ElfLoader_h
#include <vector>
#include <dlfcn.h>
#include <signal.h>
#include "mozilla/RefPtr.h"
#include "mozilla/UniquePtr.h"
#include "Zip.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(void *addr, Dl_info *info);
struct dl_phdr_info {
Elf::Addr dlpi_addr;
const char *dlpi_name;
const Elf::Phdr *dlpi_phdr;
Elf::Half dlpi_phnum;
};
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
/**
* faulty.lib public API
*/
MFBT_API size_t
__dl_get_mappable_length(void *handle);
MFBT_API void *
__dl_mmap(void *handle, void *addr, size_t length, off_t offset);
MFBT_API void
__dl_munmap(void *handle, void *addr, size_t length);
MFBT_API bool
IsSignalHandlingBroken();
}
/* 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;
template <> inline RefCounted<LibHandle, AtomicRefCount>::~RefCounted()
{
MOZ_ASSERT(mRefCnt == 0x7fffdead);
}
} /* 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()
{
++directRefCnt;
mozilla::external::AtomicRefCounted<LibHandle>::AddRef();
}
/**
* Releases a direct reference, and returns whether there are any direct
* references left.
*/
bool ReleaseDirectRef()
{
bool ret = false;
if (directRefCnt) {
MOZ_ASSERT(directRefCnt <=
mozilla::external::AtomicRefCounted<LibHandle>::refCount());
if (--directRefCnt)
ret = true;
mozilla::external::AtomicRefCounted<LibHandle>::Release();
}
return ret;
}
/**
* Returns the number of direct references
*/
MozRefCountType DirectRefCount()
{
return directRefCnt;
}
/**
* Returns the complete size of the file or stream behind the library
* handle.
*/
size_t GetMappableLength() const;
/**
* Returns a memory mapping of the file or stream behind the library
* handle.
*/
void *MappableMMap(void *addr, size_t length, off_t offset) const;
/**
* Unmaps a memory mapping of the file or stream behind the library
* handle.
*/
void MappableMUnmap(void *addr, size_t length) const;
#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
/**
* Shows some stats about the Mappable instance. The when argument is to be
* used by the caller to give an identifier of the when the stats call is
* made.
*/
virtual void stats(const char *when) const { };
protected:
/**
* Returns a mappable object for use by MappableMMap and related functions.
*/
virtual Mappable *GetMappable() const = 0;
/**
* 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;
virtual BaseElf *AsBaseElf() { return nullptr; }
virtual SystemElf *AsSystemElf() { return nullptr; }
private:
MozRefCountType directRefCnt;
char *path;
/* Mappable object keeping the result of GetMappable() */
mutable mozilla::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 = 1;
#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 mozilla::TemporaryRef<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:
virtual Mappable *GetMappable() const;
/**
* 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;
}
bool isSignalHandlingBroken() {
return signalHandlingBroken;
}
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 signalHandlingBroken;
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.
*/
mozilla::TemporaryRef<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().
*/
mozilla::TemporaryRef<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);
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);
/* Last error. Used for dlerror() */
friend class SystemElf;
friend const char *__wrap_dlerror(void);
friend void *__wrap_dlsym(void *handle, const char *symbol);
friend int __wrap_dlclose(void *handle);
const char *lastError;
private:
~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. */
mozilla::RefPtr<LibHandle> self_elf;
#if defined(ANDROID)
/* System loader handle for the libc. This is used to resolve weak symbols
* that some libcs contain that the Android linker won't dlsym(). Normally,
* we wouldn't treat non-Android differently, but glibc uses versioned
* symbols which this linker doesn't support. */
mozilla::RefPtr<LibHandle> libc;
#endif
/* Bookkeeping */
typedef std::vector<LibHandle *> LibHandleList;
LibHandleList handles;
protected:
friend class CustomElf;
friend class LoadedElf;
/**
* Show some stats about Mappables in CustomElfs. The when argument is to
* be used by the caller to give an identifier of the when the stats call
* is made.
*/
static void stats(const char *when);
/* 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);
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;
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 */