зеркало из https://github.com/mozilla/gecko-dev.git
Bug 1077384 - Make libmozglue a pseudo-LD_PRELOAD on android. r=nfroyd
In order to avoid adding more dlsym overhead than there already is, resolve symbols directly in the library containing the linker. (GetSymbolPtr is essentially free ; dlsym makes the system linker compule a ElfHash itself, and that's quite expensive to do on all symbols) This also paves the way for direct symbol resolution in all system libraries.
This commit is contained in:
Mike Hommey
Родитель
417a2977b3
Коммит
464da0f9c2
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@ -0,0 +1,55 @@
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/* 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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#include "BaseElf.h"
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#include "Elfxx.h"
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#include "Logging.h"
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using namespace Elf;
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unsigned long
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BaseElf::Hash(const char *symbol)
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{
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const unsigned char *sym = reinterpret_cast<const unsigned char *>(symbol);
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unsigned long h = 0, g;
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while (*sym) {
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h = (h << 4) + *sym++;
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g = h & 0xf0000000;
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h ^= g;
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h ^= g >> 24;
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}
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return h;
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}
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void *
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BaseElf::GetSymbolPtr(const char *symbol, unsigned long hash) const
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{
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const Sym *sym = GetSymbol(symbol, hash);
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void *ptr = nullptr;
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if (sym && sym->st_shndx != SHN_UNDEF)
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ptr = GetPtr(sym->st_value);
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DEBUG_LOG("BaseElf::GetSymbolPtr(%p [\"%s\"], \"%s\") = %p",
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reinterpret_cast<const void *>(this), GetPath(), symbol, ptr);
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return ptr;
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}
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const Sym *
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BaseElf::GetSymbol(const char *symbol, unsigned long hash) const
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{
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/* Search symbol with the buckets and chains tables.
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* The hash computed from the symbol name gives an index in the buckets
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* table. The corresponding value in the bucket table is an index in the
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* symbols table and in the chains table.
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* If the corresponding symbol in the symbols table matches, we're done.
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* Otherwise, the corresponding value in the chains table is a new index
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* in both tables, which corresponding symbol is tested and so on and so
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* forth */
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size_t bucket = hash % buckets.numElements();
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for (size_t y = buckets[bucket]; y != STN_UNDEF; y = chains[y]) {
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if (strcmp(symbol, strtab.GetStringAt(symtab[y].st_name)))
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continue;
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return &symtab[y];
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}
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return nullptr;
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}
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@ -0,0 +1,93 @@
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/* 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 BaseElf_h
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#define BaseElf_h
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#include "ElfLoader.h"
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#include "Elfxx.h"
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/**
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* Base class for ELF libraries. This class includes things that will be
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* common between SystemElfs and CustomElfs.
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*/
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class BaseElf: public LibHandle
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{
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public:
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/**
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* Hash function for symbol lookup, as defined in ELF standard for System V.
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*/
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static unsigned long Hash(const char *symbol);
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/**
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* Returns the address corresponding to the given symbol name (with a
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* pre-computed hash).
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*/
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void *GetSymbolPtr(const char *symbol, unsigned long hash) const;
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/**
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* Returns a pointer to the Elf Symbol in the Dynamic Symbol table
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* corresponding to the given symbol name (with a pre-computed hash).
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*/
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const Elf::Sym *GetSymbol(const char *symbol, unsigned long hash) const;
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BaseElf(const char *path)
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: LibHandle(path) { }
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protected:
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/**
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* Inherited from LibHandle. Those are temporary and are not supposed to
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* be used.
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*/
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virtual void *GetSymbolPtr(const char *symbol) const { return NULL; };
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virtual bool Contains(void *addr) const { return false; };
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virtual void *GetBase() const { return GetPtr(0); }
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#ifdef __ARM_EABI__
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virtual const void *FindExidx(int *pcount) const { return NULL; };
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#endif
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virtual Mappable *GetMappable() const { return NULL; };
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public:
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/* private: */
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/**
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* Returns a pointer relative to the base address where the library is
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* loaded.
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*/
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void *GetPtr(const Elf::Addr offset) const
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{
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if (reinterpret_cast<void *>(offset) > base)
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return reinterpret_cast<void *>(offset);
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return base + offset;
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}
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/**
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* Like the above, but returns a typed (const) pointer
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*/
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template <typename T>
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const T *GetPtr(const Elf::Addr offset) const
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{
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if (reinterpret_cast<void *>(offset) > base)
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return reinterpret_cast<const T *>(offset);
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return reinterpret_cast<const T *>(base + offset);
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}
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/* Base address where the library is loaded */
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MappedPtr base;
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/* Buckets and chains for the System V symbol hash table */
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Array<Elf::Word> buckets;
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UnsizedArray<Elf::Word> chains;
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/* protected: */
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/* String table */
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Elf::Strtab strtab;
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/* Symbol table */
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UnsizedArray<Elf::Sym> symtab;
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};
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#endif /* BaseElf_h */
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@ -7,7 +7,9 @@
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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 <string.h>
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#include "CustomElf.h"
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#include "BaseElf.h"
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#include "Mappable.h"
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#include "Logging.h"
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@ -279,43 +281,10 @@ CustomElf::~CustomElf()
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ElfLoader::Singleton.Forget(this);
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}
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namespace {
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/**
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* Hash function for symbol lookup, as defined in ELF standard for System V
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*/
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unsigned long
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ElfHash(const char *symbol)
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{
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const unsigned char *sym = reinterpret_cast<const unsigned char *>(symbol);
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unsigned long h = 0, g;
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while (*sym) {
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h = (h << 4) + *sym++;
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if ((g = h & 0xf0000000))
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h ^= g >> 24;
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h &= ~g;
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}
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return h;
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}
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} /* anonymous namespace */
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void *
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CustomElf::GetSymbolPtr(const char *symbol) const
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{
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return GetSymbolPtr(symbol, ElfHash(symbol));
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}
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void *
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CustomElf::GetSymbolPtr(const char *symbol, unsigned long hash) const
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{
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const Sym *sym = GetSymbol(symbol, hash);
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void *ptr = nullptr;
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if (sym && sym->st_shndx != SHN_UNDEF)
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ptr = GetPtr(sym->st_value);
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DEBUG_LOG("CustomElf::GetSymbolPtr(%p [\"%s\"], \"%s\") = %p",
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reinterpret_cast<const void *>(this), GetPath(), symbol, ptr);
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return ptr;
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return BaseElf::GetSymbolPtr(symbol, Hash(symbol));
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}
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void *
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@ -372,16 +341,17 @@ CustomElf::GetSymbolPtrInDeps(const char *symbol) const
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}
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void *sym;
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/* Search the symbol in the main program. Note this also tries all libraries
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* the system linker will have loaded RTLD_GLOBAL. Unfortunately, that doesn't
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* work with bionic, but its linker doesn't normally search the main binary
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* anyways. Moreover, on android, the main binary is dalvik. */
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#ifdef __GLIBC__
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sym = dlsym(RTLD_DEFAULT, symbol);
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DEBUG_LOG("dlsym(RTLD_DEFAULT, \"%s\") = %p", symbol, sym);
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if (sym)
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return sym;
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#endif
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unsigned long hash = Hash(symbol);
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/* self_elf should never be NULL, but better safe than sorry. */
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if (ElfLoader::Singleton.self_elf) {
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/* We consider the library containing this code a permanent LD_PRELOAD,
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* so, check if the symbol exists here first. */
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sym = ElfLoader::Singleton.self_elf->GetSymbolPtr(symbol, hash);
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if (sym)
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return sym;
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}
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/* Then search the symbol in our dependencies. Since we already searched in
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* libraries the system linker loaded, skip those (on glibc systems). We
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@ -389,15 +359,13 @@ CustomElf::GetSymbolPtrInDeps(const char *symbol) const
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* directly, not in their own dependent libraries. Building libraries with
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* --no-allow-shlib-undefined ensures such indirect symbol dependency don't
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* happen. */
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unsigned long hash = ElfHash(symbol);
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for (std::vector<RefPtr<LibHandle> >::const_iterator it = dependencies.begin();
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it < dependencies.end(); ++it) {
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if (!(*it)->IsSystemElf()) {
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sym = reinterpret_cast<CustomElf *>((*it).get())->GetSymbolPtr(symbol, hash);
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#ifndef __GLIBC__
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sym = static_cast<BaseElf *>(
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static_cast<CustomElf *>((*it).get()))->GetSymbolPtr(symbol, hash);
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} else {
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sym = (*it)->GetSymbolPtr(symbol);
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#endif
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}
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if (sym)
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return sym;
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@ -405,26 +373,6 @@ CustomElf::GetSymbolPtrInDeps(const char *symbol) const
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return nullptr;
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}
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const Sym *
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CustomElf::GetSymbol(const char *symbol, unsigned long hash) const
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{
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/* Search symbol with the buckets and chains tables.
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* The hash computed from the symbol name gives an index in the buckets
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* table. The corresponding value in the bucket table is an index in the
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* symbols table and in the chains table.
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* If the corresponding symbol in the symbols table matches, we're done.
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* Otherwise, the corresponding value in the chains table is a new index
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* in both tables, which corresponding symbol is tested and so on and so
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* forth */
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size_t bucket = hash % buckets.numElements();
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for (size_t y = buckets[bucket]; y != STN_UNDEF; y = chains[y]) {
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if (strcmp(symbol, strtab.GetStringAt(symtab[y].st_name)))
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continue;
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return &symtab[y];
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}
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return nullptr;
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}
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bool
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CustomElf::Contains(void *addr) const
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{
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@ -6,6 +6,7 @@
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#define CustomElf_h
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#include "ElfLoader.h"
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#include "BaseElf.h"
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#include "Logging.h"
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#include "Elfxx.h"
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@ -13,7 +14,7 @@
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* Library Handle class for ELF libraries we don't let the system linker
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* handle.
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*/
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class CustomElf: public LibHandle, private ElfLoader::link_map
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class CustomElf: public BaseElf, private ElfLoader::link_map
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{
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friend class ElfLoader;
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friend class SEGVHandler;
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@ -31,7 +32,7 @@ public:
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const char *path, int flags);
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/**
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* Inherited from LibHandle
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* Inherited from LibHandle/BaseElf
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*/
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virtual ~CustomElf();
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virtual void *GetSymbolPtr(const char *symbol) const;
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@ -54,18 +55,6 @@ public:
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void stats(const char *when) const;
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private:
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/**
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* Returns a pointer to the Elf Symbol in the Dynamic Symbol table
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* corresponding to the given symbol name (with a pre-computed hash).
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*/
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const Elf::Sym *GetSymbol(const char *symbol, unsigned long hash) const;
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/**
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* Returns the address corresponding to the given symbol name (with a
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* pre-computed hash).
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*/
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void *GetSymbolPtr(const char *symbol, unsigned long hash) const;
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|
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/**
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* Scan dependent libraries to find the address corresponding to the
|
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* given symbol name. This is used to find symbols that are undefined
|
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|
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@ -77,7 +66,7 @@ private:
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* Private constructor
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*/
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CustomElf(Mappable *mappable, const char *path)
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: LibHandle(path)
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: BaseElf(path)
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, mappable(mappable)
|
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, init(0)
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, fini(0)
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|
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@ -85,24 +74,6 @@ private:
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, has_text_relocs(false)
|
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{ }
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|
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/**
|
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* Returns a pointer relative to the base address where the library is
|
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* loaded.
|
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*/
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void *GetPtr(const Elf::Addr offset) const
|
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{
|
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return base + offset;
|
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}
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|
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/**
|
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* Like the above, but returns a typed (const) pointer
|
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*/
|
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template <typename T>
|
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const T *GetPtr(const Elf::Addr offset) const
|
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{
|
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return reinterpret_cast<const T *>(base + offset);
|
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}
|
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|
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/**
|
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* Loads an Elf segment defined by the given PT_LOAD header.
|
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* Returns whether this succeeded or failed.
|
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|
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@ -167,19 +138,6 @@ private:
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/* Appropriated Mappable */
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mozilla::RefPtr<Mappable> mappable;
|
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|
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/* Base address where the library is loaded */
|
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MappedPtr base;
|
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|
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/* String table */
|
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Elf::Strtab strtab;
|
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|
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/* Symbol table */
|
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UnsizedArray<Elf::Sym> symtab;
|
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|
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/* Buckets and chains for the System V symbol hash table */
|
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Array<Elf::Word> buckets;
|
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UnsizedArray<Elf::Word> chains;
|
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|
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/* List of dependent libraries */
|
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std::vector<mozilla::RefPtr<LibHandle> > dependencies;
|
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|
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|
|
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|
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@ -11,6 +11,7 @@
|
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#include <algorithm>
|
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#include <fcntl.h>
|
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#include "ElfLoader.h"
|
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#include "BaseElf.h"
|
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#include "CustomElf.h"
|
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#include "Mappable.h"
|
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#include "Logging.h"
|
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|
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@ -38,6 +39,10 @@ extern "C" MOZ_EXPORT const void *
|
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__gnu_Unwind_Find_exidx(void *pc, int *pcount) __attribute__((weak));
|
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#endif
|
||||
|
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/* Pointer to the PT_DYNAMIC section of the executable or library
|
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* containing this code. */
|
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extern "C" Elf::Dyn _DYNAMIC[];
|
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|
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using namespace mozilla;
|
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|
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/**
|
||||
|
|
@ -331,6 +336,10 @@ ElfLoader::Load(const char *path, int flags, LibHandle *parent)
|
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/* Ensure logging is initialized or refresh if environment changed. */
|
||||
Logging::Init();
|
||||
|
||||
/* Ensure self_elf initialization. */
|
||||
if (!self_elf)
|
||||
Init();
|
||||
|
||||
RefPtr<LibHandle> handle;
|
||||
|
||||
/* Handle dlopen(nullptr) directly. */
|
||||
|
|
@ -466,6 +475,54 @@ ElfLoader::Forget(LibHandle *handle)
|
|||
}
|
||||
}
|
||||
|
||||
void
|
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ElfLoader::Init()
|
||||
{
|
||||
Dl_info info;
|
||||
/* On Android < 4.1 can't reenter dl* functions. So when the library
|
||||
* containing this code is dlopen()ed, it can't call dladdr from a
|
||||
* static initializer. */
|
||||
if (dladdr(_DYNAMIC, &info) != 0) {
|
||||
/* Ideally, we wouldn't be initializing self_elf this way, but until
|
||||
* SystemElf actually inherits from BaseElf, we'll just do it this
|
||||
* (gross) way. */
|
||||
UniquePtr<BaseElf> elf = mozilla::MakeUnique<BaseElf>(info.dli_fname);
|
||||
elf->base.Assign(info.dli_fbase, -1);
|
||||
size_t symnum = 0;
|
||||
for (const Elf::Dyn *dyn = _DYNAMIC; dyn->d_tag; dyn++) {
|
||||
switch (dyn->d_tag) {
|
||||
case DT_HASH:
|
||||
{
|
||||
DEBUG_LOG("%s 0x%08" PRIxAddr, "DT_HASH", dyn->d_un.d_val);
|
||||
const Elf::Word *hash_table_header = \
|
||||
elf->GetPtr<Elf::Word>(dyn->d_un.d_ptr);
|
||||
symnum = hash_table_header[1];
|
||||
elf->buckets.Init(&hash_table_header[2], hash_table_header[0]);
|
||||
elf->chains.Init(&*elf->buckets.end());
|
||||
}
|
||||
break;
|
||||
case DT_STRTAB:
|
||||
DEBUG_LOG("%s 0x%08" PRIxAddr, "DT_STRTAB", dyn->d_un.d_val);
|
||||
elf->strtab.Init(elf->GetPtr(dyn->d_un.d_ptr));
|
||||
break;
|
||||
case DT_SYMTAB:
|
||||
DEBUG_LOG("%s 0x%08" PRIxAddr, "DT_SYMTAB", dyn->d_un.d_val);
|
||||
elf->symtab.Init(elf->GetPtr(dyn->d_un.d_ptr));
|
||||
break;
|
||||
}
|
||||
}
|
||||
if (!elf->buckets || !symnum) {
|
||||
ERROR("%s: Missing or broken DT_HASH", info.dli_fname);
|
||||
} else if (!elf->strtab) {
|
||||
ERROR("%s: Missing DT_STRTAB", info.dli_fname);
|
||||
} else if (!elf->symtab) {
|
||||
ERROR("%s: Missing DT_SYMTAB", info.dli_fname);
|
||||
} else {
|
||||
self_elf = Move(elf);
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
ElfLoader::~ElfLoader()
|
||||
{
|
||||
LibHandleList list;
|
||||
|
|
@ -507,6 +564,10 @@ ElfLoader::~ElfLoader()
|
|||
}
|
||||
}
|
||||
}
|
||||
/* Avoid self_elf->base destructor unmapping something that doesn't actually
|
||||
* belong to it. */
|
||||
if (self_elf)
|
||||
self_elf->base.release();
|
||||
}
|
||||
|
||||
void
|
||||
|
|
|
|||
|
|
@ -9,6 +9,7 @@
|
|||
#include <dlfcn.h>
|
||||
#include <signal.h>
|
||||
#include "mozilla/RefPtr.h"
|
||||
#include "mozilla/UniquePtr.h"
|
||||
#include "Zip.h"
|
||||
#include "Elfxx.h"
|
||||
#include "Mappable.h"
|
||||
|
|
@ -63,6 +64,9 @@ IsSignalHandlingBroken();
|
|||
|
||||
}
|
||||
|
||||
/* Forward declaration because BaseElf.h includes ElfLoader.h */
|
||||
class BaseElf;
|
||||
|
||||
/**
|
||||
* Specialize RefCounted template for LibHandle. We may get references to
|
||||
* LibHandles during the execution of their destructor, so we need
|
||||
|
|
@ -439,6 +443,13 @@ protected:
|
|||
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::UniquePtr<BaseElf> self_elf;
|
||||
|
||||
/* Bookkeeping */
|
||||
typedef std::vector<LibHandle *> LibHandleList;
|
||||
LibHandleList handles;
|
||||
|
|
@ -557,6 +568,12 @@ private:
|
|||
} 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
|
||||
|
|
@ -564,6 +581,8 @@ private:
|
|||
public:
|
||||
DebuggerHelper();
|
||||
|
||||
void Init(AuxVector *auvx);
|
||||
|
||||
operator bool()
|
||||
{
|
||||
return dbg;
|
||||
|
|
|
|||
|
|
@ -290,6 +290,10 @@ public:
|
|||
static_cast<T *>(this)->munmap(get(), GetLength());
|
||||
}
|
||||
|
||||
void release()
|
||||
{
|
||||
MemoryRange::Assign(MAP_FAILED, 0);
|
||||
}
|
||||
};
|
||||
|
||||
struct MappedPtr: public GenericMappedPtr<MappedPtr>
|
||||
|
|
|
|||
|
|
@ -5,6 +5,7 @@
|
|||
# file, You can obtain one at http://mozilla.org/MPL/2.0/.
|
||||
|
||||
SOURCES += [
|
||||
'BaseElf.cpp',
|
||||
'CustomElf.cpp',
|
||||
'ElfLoader.cpp',
|
||||
'Mappable.cpp',
|
||||
|
|
|
|||
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