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/*
* Copyright 2017 The Abseil Authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
// Allow dynamic symbol lookup for in-memory Elf images.
#ifndef ABSL_DEBUGGING_INTERNAL_ELF_MEM_IMAGE_H_
#define ABSL_DEBUGGING_INTERNAL_ELF_MEM_IMAGE_H_
// Including this will define the __GLIBC__ macro if glibc is being
// used.
#include <climits>
// Maybe one day we can rewrite this file not to require the elf
// symbol extensions in glibc, but for right now we need them.
#ifdef ABSL_HAVE_ELF_MEM_IMAGE
#error ABSL_HAVE_ELF_MEM_IMAGE cannot be directly set
#endif
#if defined(__ELF__) && defined(__GLIBC__) && !defined(__native_client__) && \
!defined(__asmjs__)
#define ABSL_HAVE_ELF_MEM_IMAGE 1
#endif
#if ABSL_HAVE_ELF_MEM_IMAGE
#include <link.h> // for ElfW
namespace absl {
namespace debugging_internal {
// An in-memory ELF image (may not exist on disk).
class ElfMemImage {
private:
// Sentinel: there could never be an elf image at &kInvalidBaseSentinel.
static const int kInvalidBaseSentinel;
public:
// Sentinel: there could never be an elf image at this address.
static constexpr const void *const kInvalidBase =
static_cast<const void*>(&kInvalidBaseSentinel);
// Information about a single vdso symbol.
// All pointers are into .dynsym, .dynstr, or .text of the VDSO.
// Do not free() them or modify through them.
struct SymbolInfo {
const char *name; // E.g. "__vdso_getcpu"
const char *version; // E.g. "LINUX_2.6", could be ""
// for unversioned symbol.
const void *address; // Relocated symbol address.
const ElfW(Sym) *symbol; // Symbol in the dynamic symbol table.
};
// Supports iteration over all dynamic symbols.
class SymbolIterator {
public:
friend class ElfMemImage;
const SymbolInfo *operator->() const;
const SymbolInfo &operator*() const;
SymbolIterator& operator++();
bool operator!=(const SymbolIterator &rhs) const;
bool operator==(const SymbolIterator &rhs) const;
private:
SymbolIterator(const void *const image, int index);
void Update(int incr);
SymbolInfo info_;
int index_;
const void *const image_;
};
explicit ElfMemImage(const void *base);
void Init(const void *base);
bool IsPresent() const { return ehdr_ != nullptr; }
const ElfW(Phdr)* GetPhdr(int index) const;
const ElfW(Sym)* GetDynsym(int index) const;
const ElfW(Versym)* GetVersym(int index) const;
const ElfW(Verdef)* GetVerdef(int index) const;
const ElfW(Verdaux)* GetVerdefAux(const ElfW(Verdef) *verdef) const;
const char* GetDynstr(ElfW(Word) offset) const;
const void* GetSymAddr(const ElfW(Sym) *sym) const;
const char* GetVerstr(ElfW(Word) offset) const;
int GetNumSymbols() const;
SymbolIterator begin() const;
SymbolIterator end() const;
// Look up versioned dynamic symbol in the image.
// Returns false if image is not present, or doesn't contain given
// symbol/version/type combination.
// If info_out is non-null, additional details are filled in.
bool LookupSymbol(const char *name, const char *version,
int symbol_type, SymbolInfo *info_out) const;
// Find info about symbol (if any) which overlaps given address.
// Returns true if symbol was found; false if image isn't present
// or doesn't have a symbol overlapping given address.
// If info_out is non-null, additional details are filled in.
bool LookupSymbolByAddress(const void *address, SymbolInfo *info_out) const;
private:
const ElfW(Ehdr) *ehdr_;
const ElfW(Sym) *dynsym_;
const ElfW(Versym) *versym_;
const ElfW(Verdef) *verdef_;
const ElfW(Word) *hash_;
const char *dynstr_;
size_t strsize_;
size_t verdefnum_;
ElfW(Addr) link_base_; // Link-time base (p_vaddr of first PT_LOAD).
};
} // namespace debugging_internal
} // namespace absl
#endif // ABSL_HAVE_ELF_MEM_IMAGE
#endif // ABSL_DEBUGGING_INTERNAL_ELF_MEM_IMAGE_H_
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