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// Copyright 2014 The Crashpad Authors. All rights reserved.
// 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
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
#include <map>
#include <string>
#include <mach/mach.h>
#include <stdint.h>
#include "base/macros.h"
#include "snapshot/mac/mach_o_image_segment_reader.h"
#include "snapshot/mac/process_reader_mac.h"
#include "snapshot/mac/process_types.h"
#include "util/misc/initialization_state_dcheck.h"
namespace crashpad {
//! \brief A reader for symbol tables in Mach-O images mapped into another
//! process.
class MachOImageSymbolTableReader {
//! \brief Information about a symbol in a module’s symbol table.
//! This is a more minimal form of the `nlist` (or `nlist_64`) structure,
//! only containing the equivalent of the `n_value` and `n_sect` fields.
struct SymbolInformation {
//! \brief The address of the symbol as it exists in the symbol table, not
//! adjusted for any “slide.”
mach_vm_address_t value;
//! \brief The 1-based section index in the module in which the symbol is
//! found.
//! For symbols defined in a section (`N_SECT`), this is the section index
//! that can be passed to MachOImageReader::GetSectionAtIndex(), and \a
//! value will need to be adjusted for segment slide if the containing
//! segment slid when loaded. For absolute symbols (`N_ABS`), this will be
//! `NO_SECT` (`0`), and \a value must not be adjusted for segment slide.
uint8_t section;
// TODO(mark): Use std::unordered_map or a similar hash-based map? For now,
// std::map is fine because this map only stores external defined symbols, and
// there aren’t expected to be very many of those that performance would
// become a problem. In reality, std::unordered_map does not appear to provide
// a performance advantage. It appears that the memory copies currently done
// by ProcessMemoryMac::Read() have substantially more impact on symbol table
// operations.
// This is public so that the type is available to
// MachOImageSymbolTableReaderInitializer.
using SymbolInformationMap = std::map<std::string, SymbolInformation>;
//! \brief Reads the symbol table from another process.
//! This method must only be called once on an object. This method must be
//! called successfully before any other method in this class may be called.
//! \param[in] process_reader The reader for the remote process.
//! \param[in] symtab_command The `LC_SYMTAB` load command that identifies
//! the symbol table.
//! \param[in] dysymtab_command The `LC_DYSYMTAB` load command that identifies
//! dynamic symbol information within the symbol table. This load command
//! is not present in all modules, and this parameter may be `nullptr` for
//! modules that do not have this information. When present, \a
//! dysymtab_command is an optimization that allows the symbol table
//! reader to only examine symbol table entries known to be relevant for
//! its purposes.
//! \param[in] linkedit_segment The `__LINKEDIT` segment. This segment should
//! contain the data referenced by \a symtab_command and \a
//! dysymtab_command. This may be any segment in the module, but by
//! convention, the name `__LINKEDIT` is used for this purpose.
//! \param[in] module_info A string to be used in logged messages. This string
//! is for diagnostic purposes only, and may be empty.
//! \return `true` if the symbol table was read successfully. `false`
//! otherwise, with an appropriate message logged.
bool Initialize(ProcessReaderMac* process_reader,
const process_types::symtab_command* symtab_command,
const process_types::dysymtab_command* dysymtab_command,
const MachOImageSegmentReader* linkedit_segment,
const std::string& module_info);
//! \brief Looks up a symbol in the image’s symbol table.
//! The returned information captures the symbol as it exists in the image’s
//! symbol table, not adjusted for any “slide.”
//! \param[in] name The name of the symbol to look up, “mangled” or
//! “decorated” appropriately. For example, use `"_main"` to look up the
//! symbol for the C `main()` function, and use `"__Z4Funcv"` to look up
//! the symbol for the C++ `Func()` function.
//! \return A SymbolInformation* object with information about the symbol if
//! it was found, or `nullptr` if the symbol was not found or if an error
//! occurred. On error, a warning message will also be logged. The caller
//! does not take ownership; the lifetime of the returned object is scoped
//! to the lifetime of this MachOImageSymbolTableReader object.
//! \note Symbol values returned via this interface are not adjusted for
//! “slide.” For slide-adjusted values, use the higher-level
//! MachOImageReader::LookUpExternalDefinedSymbol() interface.
const SymbolInformation* LookUpExternalDefinedSymbol(
const std::string& name) const;
SymbolInformationMap external_defined_symbols_;
InitializationStateDcheck initialized_;
} // namespace crashpad