mirror of
https://github.com/mozilla/gecko-dev.git
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524 lines
14 KiB
C++
524 lines
14 KiB
C++
/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this file,
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* You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef ElfLoader_h
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#define ElfLoader_h
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#include <vector>
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#include <dlfcn.h>
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#include <signal.h>
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#include "mozilla/RefPtr.h"
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#include "Zip.h"
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#include "Elfxx.h"
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/**
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* dlfcn.h replacement functions
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*/
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extern "C" {
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void *__wrap_dlopen(const char *path, int flags);
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const char *__wrap_dlerror(void);
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void *__wrap_dlsym(void *handle, const char *symbol);
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int __wrap_dlclose(void *handle);
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#ifndef HAVE_DLADDR
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typedef struct {
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const char *dli_fname;
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void *dli_fbase;
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const char *dli_sname;
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void *dli_saddr;
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} Dl_info;
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#endif
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int __wrap_dladdr(void *addr, Dl_info *info);
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sighandler_t __wrap_signal(int signum, sighandler_t handler);
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int __wrap_sigaction(int signum, const struct sigaction *act,
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struct sigaction *oldact);
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struct dl_phdr_info {
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Elf::Addr dlpi_addr;
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const char *dlpi_name;
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const Elf::Phdr *dlpi_phdr;
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Elf::Half dlpi_phnum;
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};
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typedef int (*dl_phdr_cb)(struct dl_phdr_info *, size_t, void *);
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int __wrap_dl_iterate_phdr(dl_phdr_cb callback, void *data);
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}
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/**
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* Specialize RefCounted template for LibHandle. We may get references to
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* LibHandles during the execution of their destructor, so we need
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* RefCounted<LibHandle>::Release to support some reentrancy. See further
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* below.
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*/
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class LibHandle;
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namespace mozilla {
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template <> inline void RefCounted<LibHandle>::Release();
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template <> inline RefCounted<LibHandle>::~RefCounted()
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{
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MOZ_ASSERT(refCnt == 0x7fffdead);
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}
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} /* namespace mozilla */
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/**
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* Abstract class for loaded libraries. Libraries may be loaded through the
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* system linker or this linker, both cases will be derived from this class.
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*/
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class LibHandle: public mozilla::RefCounted<LibHandle>
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{
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public:
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/**
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* Constructor. Takes the path of the loaded library and will store a copy
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* of the leaf name.
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*/
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LibHandle(const char *path)
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: directRefCnt(0), path(path ? strdup(path) : NULL) { }
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/**
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* Destructor.
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*/
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virtual ~LibHandle();
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/**
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* Returns the pointer to the address to which the given symbol resolves
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* inside the library. It is not supposed to resolve the symbol in other
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* libraries, although in practice, it will for system libraries.
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*/
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virtual void *GetSymbolPtr(const char *symbol) const = 0;
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/**
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* Returns whether the given address is part of the virtual address space
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* covered by the loaded library.
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*/
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virtual bool Contains(void *addr) const = 0;
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/**
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* Returns the file name of the library without the containing directory.
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*/
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const char *GetName() const;
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/**
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* Returns the full path of the library, when available. Otherwise, returns
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* the file name.
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*/
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const char *GetPath() const
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{
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return path;
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}
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/**
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* Library handles can be referenced from other library handles or
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* externally (when dlopen()ing using this linker). We need to be
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* able to distinguish between the two kind of referencing for better
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* bookkeeping.
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*/
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void AddDirectRef()
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{
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++directRefCnt;
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mozilla::RefCounted<LibHandle>::AddRef();
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}
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/**
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* Releases a direct reference, and returns whether there are any direct
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* references left.
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*/
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bool ReleaseDirectRef()
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{
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bool ret = false;
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if (directRefCnt) {
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MOZ_ASSERT(directRefCnt <= mozilla::RefCounted<LibHandle>::refCount());
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if (--directRefCnt)
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ret = true;
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mozilla::RefCounted<LibHandle>::Release();
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}
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return ret;
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}
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/**
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* Returns the number of direct references
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*/
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int DirectRefCount()
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{
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return directRefCnt;
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}
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protected:
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/**
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* Returns whether the handle is a SystemElf or not. (short of a better way
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* to do this without RTTI)
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*/
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friend class ElfLoader;
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friend class CustomElf;
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friend class SEGVHandler;
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virtual bool IsSystemElf() const { return false; }
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private:
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int directRefCnt;
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char *path;
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};
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/**
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* Specialized RefCounted<LibHandle>::Release. Under normal operation, when
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* refCnt reaches 0, the LibHandle is deleted. Its refCnt is however increased
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* to 1 on normal builds, and 0x7fffdead on debug builds so that the LibHandle
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* can still be referenced while the destructor is executing. The refCnt is
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* allowed to grow > 0x7fffdead, but not to decrease under that value, which
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* would mean too many Releases from within the destructor.
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*/
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namespace mozilla {
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template <> inline void RefCounted<LibHandle>::Release() {
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#ifdef DEBUG
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if (refCnt > 0x7fff0000)
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MOZ_ASSERT(refCnt > 0x7fffdead);
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#endif
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MOZ_ASSERT(refCnt > 0);
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if (refCnt > 0) {
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if (0 == --refCnt) {
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#ifdef DEBUG
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refCnt = 0x7fffdead;
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#else
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refCnt = 1;
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#endif
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delete static_cast<LibHandle*>(this);
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}
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}
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}
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} /* namespace mozilla */
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/**
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* Class handling libraries loaded by the system linker
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*/
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class SystemElf: public LibHandle
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{
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public:
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/**
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* Returns a new SystemElf for the given path. The given flags are passed
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* to dlopen().
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*/
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static mozilla::TemporaryRef<LibHandle> Load(const char *path, int flags);
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/**
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* Inherited from LibHandle
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*/
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virtual ~SystemElf();
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virtual void *GetSymbolPtr(const char *symbol) const;
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virtual bool Contains(void *addr) const { return false; /* UNIMPLEMENTED */ }
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protected:
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/**
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* Returns whether the handle is a SystemElf or not. (short of a better way
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* to do this without RTTI)
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*/
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friend class ElfLoader;
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virtual bool IsSystemElf() const { return true; }
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/**
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* Remove the reference to the system linker handle. This avoids dlclose()
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* being called when the instance is destroyed.
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*/
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void Forget()
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{
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dlhandle = NULL;
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}
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private:
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/**
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* Private constructor
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*/
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SystemElf(const char *path, void *handle)
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: LibHandle(path), dlhandle(handle) { }
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/* Handle as returned by system dlopen() */
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void *dlhandle;
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};
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/**
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* The ElfLoader registers its own SIGSEGV handler to handle segmentation
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* faults within the address space of the loaded libraries. It however
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* allows a handler to be set for faults in other places, and redispatches
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* to the handler set through signal() or sigaction(). We assume no system
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* library loaded with system dlopen is going to call signal or sigaction
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* for SIGSEGV.
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*/
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class SEGVHandler
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{
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protected:
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SEGVHandler();
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~SEGVHandler();
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private:
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friend sighandler_t __wrap_signal(int signum, sighandler_t handler);
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friend int __wrap_sigaction(int signum, const struct sigaction *act,
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struct sigaction *oldact);
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/**
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* SIGSEGV handler registered with __wrap_signal or __wrap_sigaction.
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*/
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struct sigaction action;
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/**
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* ElfLoader SIGSEGV handler.
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*/
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static void handler(int signum, siginfo_t *info, void *context);
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/**
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* Size of the alternative stack. The printf family requires more than 8KB
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* of stack, and our signal handler may print a few things.
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*/
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static const size_t stackSize = 12 * 1024;
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/**
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* Alternative stack information used before initialization.
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*/
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stack_t oldStack;
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/**
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* Pointer to an alternative stack for signals. Only set if oldStack is
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* not set or not big enough.
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*/
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MappedPtr stackPtr;
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};
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/**
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* Elf Loader class in charge of loading and bookkeeping libraries.
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*/
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class ElfLoader: public SEGVHandler
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{
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public:
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/**
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* The Elf Loader instance
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*/
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static ElfLoader Singleton;
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/**
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* Loads the given library with the given flags. Equivalent to dlopen()
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* The extra "parent" argument optionally gives the handle of the library
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* requesting the given library to be loaded. The loader may look in the
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* directory containing that parent library for the library to load.
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*/
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mozilla::TemporaryRef<LibHandle> Load(const char *path, int flags,
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LibHandle *parent = NULL);
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/**
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* Returns the handle of the library containing the given address in
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* its virtual address space, i.e. the library handle for which
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* LibHandle::Contains returns true. Its purpose is to allow to
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* implement dladdr().
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*/
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mozilla::TemporaryRef<LibHandle> GetHandleByPtr(void *addr);
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protected:
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/**
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* Registers the given handle. This method is meant to be called by
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* LibHandle subclass creators.
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*/
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void Register(LibHandle *handle);
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/**
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* Forget about the given handle. This method is meant to be called by
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* LibHandle subclass destructors.
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*/
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void Forget(LibHandle *handle);
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/* Last error. Used for dlerror() */
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friend class SystemElf;
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friend const char *__wrap_dlerror(void);
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friend void *__wrap_dlsym(void *handle, const char *symbol);
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friend int __wrap_dlclose(void *handle);
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const char *lastError;
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private:
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~ElfLoader();
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/* Bookkeeping */
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typedef std::vector<LibHandle *> LibHandleList;
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LibHandleList handles;
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protected:
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friend class CustomElf;
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/**
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* Show some stats about Mappables in CustomElfs. The when argument is to
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* be used by the caller to give an identifier of the when the stats call
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* is made.
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*/
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static void stats(const char *when);
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/* Definition of static destructors as to be used for C++ ABI compatibility */
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typedef void (*Destructor)(void *object);
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/**
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* C++ ABI makes static initializers register destructors through a specific
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* atexit interface. On glibc/linux systems, the dso_handle is a pointer
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* within a given library. On bionic/android systems, it is an undefined
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* symbol. Making sense of the value is not really important, and all that
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* is really important is that it is different for each loaded library, so
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* that they can be discriminated when shutting down. For convenience, on
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* systems where the dso handle is a symbol, that symbol is resolved to
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* point at corresponding CustomElf.
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*
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* Destructors are registered with __*_atexit with an associated object to
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* be passed as argument when it is called.
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*
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* When __cxa_finalize is called, destructors registered for the given
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* DSO handle are called in the reverse order they were registered.
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*/
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#ifdef __ARM_EABI__
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static int __wrap_aeabi_atexit(void *that, Destructor destructor,
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void *dso_handle);
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#else
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static int __wrap_cxa_atexit(Destructor destructor, void *that,
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void *dso_handle);
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#endif
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static void __wrap_cxa_finalize(void *dso_handle);
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/**
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* Registered destructor. Keeps track of the destructor function pointer,
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* associated object to call it with, and DSO handle.
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*/
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class DestructorCaller {
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public:
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DestructorCaller(Destructor destructor, void *object, void *dso_handle)
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: destructor(destructor), object(object), dso_handle(dso_handle) { }
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/**
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* Call the destructor function with the associated object.
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* Call only once, see CustomElf::~CustomElf.
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*/
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void Call();
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/**
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* Returns whether the destructor is associated to the given DSO handle
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*/
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bool IsForHandle(void *handle) const
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{
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return handle == dso_handle;
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}
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private:
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Destructor destructor;
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void *object;
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void *dso_handle;
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};
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private:
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/* Keep track of all registered destructors */
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std::vector<DestructorCaller> destructors;
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/* Forward declaration, see further below */
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class DebuggerHelper;
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public:
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/* Loaded object descriptor for the debugger interface below*/
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struct link_map {
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/* Base address of the loaded object. */
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const void *l_addr;
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/* File name */
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const char *l_name;
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/* Address of the PT_DYNAMIC segment. */
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const void *l_ld;
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private:
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friend class ElfLoader::DebuggerHelper;
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/* Double linked list of loaded objects. */
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link_map *l_next, *l_prev;
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};
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private:
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/* Data structure used by the linker to give details about shared objects it
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* loaded to debuggers. This is normally defined in link.h, but Android
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* headers lack this file. */
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struct r_debug {
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/* Version number of the protocol. */
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int r_version;
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/* Head of the linked list of loaded objects. */
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link_map *r_map;
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/* Function to be called when updates to the linked list of loaded objects
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* are going to occur. The function is to be called before and after
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* changes. */
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void (*r_brk)(void);
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/* Indicates to the debugger what state the linked list of loaded objects
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* is in when the function above is called. */
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enum {
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RT_CONSISTENT, /* Changes are complete */
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RT_ADD, /* Beginning to add a new object */
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RT_DELETE /* Beginning to remove an object */
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} r_state;
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};
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/* Helper class used to integrate libraries loaded by this linker in
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* r_debug */
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class DebuggerHelper
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{
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public:
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DebuggerHelper();
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operator bool()
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{
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return dbg;
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}
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/* Make the debugger aware of a new loaded object */
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void Add(link_map *map);
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/* Make the debugger aware of the unloading of an object */
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void Remove(link_map *map);
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/* Iterates over all link_maps */
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class iterator
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{
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public:
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const link_map *operator ->() const
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{
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return item;
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}
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const link_map &operator ++()
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{
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item = item->l_next;
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return *item;
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}
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bool operator<(const iterator &other) const
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{
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if (other.item == NULL)
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return item ? true : false;
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MOZ_NOT_REACHED("DebuggerHelper::iterator::operator< called with something else than DebuggerHelper::end()");
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}
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protected:
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friend class DebuggerHelper;
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iterator(const link_map *item): item(item) { }
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private:
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const link_map *item;
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};
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iterator begin() const
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{
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return iterator(dbg ? dbg->r_map : NULL);
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}
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iterator end() const
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{
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return iterator(NULL);
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}
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private:
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r_debug *dbg;
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link_map *firstAdded;
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};
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friend int __wrap_dl_iterate_phdr(dl_phdr_cb callback, void *data);
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DebuggerHelper dbg;
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};
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#endif /* ElfLoader_h */
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