// Copyright 2014 The Crashpad 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.
#ifndef CRASHPAD_SNAPSHOT_MAC_MACH_O_IMAGE_READER_H_
#define CRASHPAD_SNAPSHOT_MAC_MACH_O_IMAGE_READER_H_
#include <mach/mach.h>
#include <stdint.h>
#include <sys/types.h>
#include <map>
#include <memory>
#include <string>
#include <vector>
#include "snapshot/mac/process_types.h"
#include "util/misc/initialization_state_dcheck.h"
#include "util/misc/uuid.h"
namespace crashpad {
class MachOImageSegmentReader;
class MachOImageSymbolTableReader;
class ProcessReaderMac;
//! \brief A reader for Mach-O images mapped into another process.
//!
//! This class is capable of reading both 32-bit (`mach_header`/`MH_MAGIC`) and
//! 64-bit (`mach_header_64`/`MH_MAGIC_64`) images based on the bitness of the
//! remote process.
//!
//! \sa MachOImageAnnotationsReader
class MachOImageReader {
public:
MachOImageReader();
MachOImageReader(const MachOImageReader&) = delete;
MachOImageReader& operator=(const MachOImageReader&) = delete;
~MachOImageReader();
//! \brief Reads the Mach-O image file’s load commands 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] address The address, in the remote process’ address space,
//! where the `mach_header` or `mach_header_64` at the beginning of the
//! image to be read is located. This address can be determined by reading
//! the remote process’ dyld information (see
//! snapshot/mac/process_types/dyld_images.proctype).
//! \param[in] name The module’s name, a string to be used in logged messages.
//! This string is for diagnostic purposes and to relax otherwise strict
//! parsing rules for common modules with known defects.
//!
//! \return `true` if the image was read successfully, including all load
//! commands. `false` otherwise, with an appropriate message logged.
bool Initialize(ProcessReaderMac* process_reader,
mach_vm_address_t address,
const std::string& name);
//! \brief Returns the Mach-O file type.
//!
//! This value comes from the `filetype` field of the `mach_header` or
//! `mach_header_64`. Common values include `MH_EXECUTE`, `MH_DYLIB`,
//! `MH_DYLINKER`, and `MH_BUNDLE`.
uint32_t FileType() const { return file_type_; }
//! \brief Returns the Mach-O image’s load address.
//!
//! This is the value passed as \a address to Initialize().
mach_vm_address_t Address() const { return address_; }
//! \brief Returns the mapped size of the Mach-O image’s `__TEXT` segment.
//!
//! Note that this is returns only the size of the `__TEXT` segment, not of
//! any other segment. This is because the interface only allows one load
//! address and size to be reported, but Mach-O image files may consist of
//! multiple discontiguous segments. By convention, the `__TEXT` segment is
//! always mapped at the beginning of a Mach-O image file, and it is the most
//! useful for the expected intended purpose of collecting data to obtain
//! stack backtraces. The implementation insists during initialization that
//! the `__TEXT` segment be mapped at the beginning of the file.
//!
//! In practice, discontiguous segments are only found for images that have
//! loaded out of the dyld shared cache, but the `__TEXT` segment’s size is
//! returned for modules that loaded with contiguous segments as well for
//! consistency.
mach_vm_size_t Size() const { return size_; }
//! \brief Returns the Mach-O image’s “slide,” the difference between its
//! actual load address and its preferred load address.
//!
//! “Slide” is computed by subtracting the `__TEXT` segment’s preferred load
//! address from its actual load address. It will be reported as a positive
//! offset when the actual load address is greater than the preferred load
//! address. The preferred load address is taken to be the segment’s reported
//! `vmaddr` value.
mach_vm_size_t Slide() const { return slide_; }
//! \brief Obtain segment information by segment name.
//!
//! \param[in] segment_name The name of the segment to search for, for
//! example, `"__TEXT"`.
//!
//! \return A pointer to the segment information if it was found, or `nullptr`
//! if it was not found. The caller does not take ownership; the lifetime
//! of the returned object is scoped to the lifetime of this
//! MachOImageReader object.
const MachOImageSegmentReader* GetSegmentByName(
const std::string& segment_name) const;
//! \brief Obtain section information by segment and section name.
//!
//! \param[in] segment_name The name of the segment to search for, for
//! example, `"__TEXT"`.
//! \param[in] section_name The name of the section within the segment to
//! search for, for example, `"__text"`.
//! \param[out] address The actual address that the section was loaded at in
//! memory, taking any “slide” into account if the section did not load at
//! its preferred address as stored in the Mach-O image file. This
//! parameter can be `nullptr`.
//!
//! \return A pointer to the section information if it was found, or `nullptr`
//! if it was not found. The caller does not take ownership; the lifetime
//! of the returned object is scoped to the lifetime of this
//! MachOImageReader object.
//!
//! No parameter is provided for the section’s size, because it can be
//! obtained from the returned process_types::section::size field.
//!
//! \note The process_types::section::addr field gives the section’s preferred
//! load address as stored in the Mach-O image file, and is not adjusted
//! for any “slide” that may have occurred when the image was loaded. Use
//! \a address to obtain the section’s actual load address.
const process_types::section* GetSectionByName(
const std::string& segment_name,
const std::string& section_name,
mach_vm_address_t* address) const;
//! \brief Obtain section information by section index.
//!
//! \param[in] index The index of the section to return, in the order that it
//! appears in the segment load commands. This is a 1-based index,
//! matching the section number values used for `nlist::n_sect`.
//! \param[out] containing_segment The segment that contains the section.
//! This parameter can be `nullptr`. The caller does not take ownership;
//! the lifetime of the returned object is scoped to the lifetime of this
//! MachOImageReader object.
//! \param[out] address The actual address that the section was loaded at in
//! memory, taking any “slide” into account if the section did not load at
//! its preferred address as stored in the Mach-O image file. This
//! parameter can be `nullptr`.
//!
//! \return A pointer to the section information. If \a index is out of range,
//! logs a warning and returns `nullptr`. The caller does not take
//! ownership; the lifetime of the returned object is scoped to the
//! lifetime of this MachOImageReader object.
//!
//! No parameter is provided for the section’s size, because it can be
//! obtained from the returned process_types::section::size field.
//!
//! \note The process_types::section::addr field gives the section’s preferred
//! load address as stored in the Mach-O image file, and is not adjusted
//! for any “slide” that may have occurred when the image was loaded. Use
//! \a address to obtain the section’s actual load address.
//! \note Unlike MachOImageSegmentReader::GetSectionAtIndex(), this method
//! accepts out-of-range values for \a index, and returns `nullptr`
//! instead of aborting execution upon encountering an out-of-range value.
//! This is because a Mach-O image file’s symbol table refers to this
//! per-module section index, and an out-of-range index in that case
//! should be treated as a data error (where the data is beyond this
//! code’s control) and handled non-fatally by reporting the error to the
//! caller.
const process_types::section* GetSectionAtIndex(
size_t index,
const MachOImageSegmentReader** containing_segment,
mach_vm_address_t* address) const;
//! \brief Looks up a symbol in the image’s symbol table.
//!
//! This method is capable of locating external defined symbols. Specifically,
//! this method can look up symbols that have these charcteristics:
//! - `N_STAB` (debugging) and `N_PEXT` (private external) must not be set.
//! - `N_EXT` (external) must be set.
//! - The type must be `N_ABS` (absolute) or `N_SECT` (defined in section).
//!
//! `N_INDR` (indirect), `N_UNDF` (undefined), and `N_PBUD` (prebound
//! undefined) symbols cannot be located through this mechanism.
//!
//! \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. Contrary to `dlsym()`, the
//! leading underscore must not be stripped when using this interface.
//! \param[out] value If the lookup was successful, this will be set to the
//! value of the symbol, adjusted for any “slide” as needed. The value can
//! be used as an address in the remote process’ address space where the
//! pointee of the symbol exists in memory.
//!
//! \return `true` if the symbol lookup was successful and the symbol was
//! found. `false` otherwise, including error conditions (for which a
//! warning message will be logged), modules without symbol tables, and
//! symbol names not found in the symbol table.
//!
//! \note Symbol values returned via this interface are adjusted for “slide”
//! as appropriate, in contrast to the underlying implementation,
//! MachOImageSymbolTableReader::LookUpExternalDefinedSymbol().
//!
//! \warning Symbols that are resolved by running symbol resolvers
//! (`.symbol_resolver`) are not properly handled by this interface. The
//! address of the symbol resolver is returned because that’s what shows
//! up in the symbol table, rather than the effective address of the
//! resolved symbol as used by dyld after running the resolver. The only
//! way to detect this situation would be to read the `LC_DYLD_INFO` or
//! `LC_DYLD_INFO_ONLY` load command if present and looking for the
//! `EXPORT_SYMBOL_FLAGS_STUB_AND_RESOLVER` flag, but that would just be
//! able to detect symbols with a resolver, it would not be able to
//! resolve them from out-of-process, so it’s not currently done.
bool LookUpExternalDefinedSymbol(const std::string& name,
mach_vm_address_t* value) const;
//! \brief Returns a Mach-O dylib image’s current version.
//!
//! This information comes from the `dylib_current_version` field of a dylib’s
//! `LC_ID_DYLIB` load command. For dylibs without this load command, `0` will
//! be returned.
//!
//! This method may only be called on Mach-O images for which FileType()
//! returns `MH_DYLIB`.
uint32_t DylibVersion() const;
//! \brief Returns a Mach-O image’s source version.
//!
//! This information comes from a Mach-O image’s `LC_SOURCE_VERSION` load
//! command. For Mach-O images without this load command, `0` will be
//! returned.
uint64_t SourceVersion() const { return source_version_; }
//! \brief Returns a Mach-O image’s UUID.
//!
//! This information comes from a Mach-O image’s `LC_UUID` load command. For
//! Mach-O images without this load command, a zeroed-out UUID value will be
//! returned.
//
// UUID is a name in this scope (referring to this method), so the parameter’s
// type needs to be qualified with |crashpad::|.
void UUID(crashpad::UUID* uuid) const;
//! \brief Returns the dynamic linker’s pathname.
//!
//! The dynamic linker is normally /usr/lib/dyld.
//!
//! For executable images (those with file type `MH_EXECUTE`), this is the
//! name provided in the `LC_LOAD_DYLINKER` load command, if any. For dynamic
//! linker images (those with file type `MH_DYLINKER`), this is the name
//! provided in the `LC_ID_DYLINKER` load command. In other cases, this will
//! be empty.
std::string DylinkerName() const { return dylinker_name_; }
//! \brief Obtains the module’s CrashpadInfo structure.
//!
//! \return `true` on success, `false` on failure. If the module does not have
//! a `__DATA,crashpad_info` section, this will return `false` without
//! logging any messages. Other failures will result in messages being
//! logged.
bool GetCrashpadInfo(process_types::CrashpadInfo* crashpad_info) const;
private:
// A generic helper routine for the other Read*Command() methods.
template <typename T>
bool ReadLoadCommand(mach_vm_address_t load_command_address,
const std::string& load_command_info,
uint32_t expected_load_command_id,
T* load_command);
// The Read*Command() methods are subroutines called by Initialize(). They are
// responsible for reading a single load command. They may update the member
// fields of their MachOImageReader object. If they can’t make sense of a load
// command, they return false.
bool ReadSegmentCommand(mach_vm_address_t load_command_address,
const std::string& load_command_info);
bool ReadSymTabCommand(mach_vm_address_t load_command_address,
const std::string& load_command_info);
bool ReadDySymTabCommand(mach_vm_address_t load_command_address,
const std::string& load_command_info);
bool ReadIdDylibCommand(mach_vm_address_t load_command_address,
const std::string& load_command_info);
bool ReadDylinkerCommand(mach_vm_address_t load_command_address,
const std::string& load_command_info);
bool ReadUUIDCommand(mach_vm_address_t load_command_address,
const std::string& load_command_info);
bool ReadSourceVersionCommand(mach_vm_address_t load_command_address,
const std::string& load_command_info);
bool ReadUnexpectedCommand(mach_vm_address_t load_command_address,
const std::string& load_command_info);
// Performs deferred initialization of the symbol table. Because a module’s
// symbol table is often not needed, this is not handled in Initialize(), but
// is done lazily, on-demand as needed.
//
// symbol_table_initialized_ will be transitioned to the appropriate state. If
// initialization completes successfully, this will be the valid state.
// Otherwise, it will be left in the invalid state and a warning message will
// be logged.
//
// Note that if the object contains no symbol table, symbol_table_initialized_
// will be set to the valid state, but symbol_table_ will be nullptr.
void InitializeSymbolTable() const;
std::vector<std::unique_ptr<MachOImageSegmentReader>> segments_;
std::map<std::string, size_t> segment_map_;
std::string module_name_;
std::string module_info_;
std::string dylinker_name_;
crashpad::UUID uuid_;
mach_vm_address_t address_;
mach_vm_size_t size_;
mach_vm_size_t slide_;
uint64_t source_version_;
std::unique_ptr<process_types::symtab_command> symtab_command_;
std::unique_ptr<process_types::dysymtab_command> dysymtab_command_;
// symbol_table_ (and symbol_table_initialized_) are mutable in order to
// maintain LookUpExternalDefinedSymbol() as a const interface while allowing
// lazy initialization via InitializeSymbolTable(). This is logical
// const-ness, not physical const-ness.
mutable std::unique_ptr<MachOImageSymbolTableReader> symbol_table_;
std::unique_ptr<process_types::dylib_command> id_dylib_command_;
ProcessReaderMac* process_reader_; // weak
uint32_t file_type_;
InitializationStateDcheck initialized_;
// symbol_table_initialized_ protects symbol_table_: symbol_table_ can only
// be used when symbol_table_initialized_ is valid, although
// symbol_table_initialized_ being valid doesn’t imply that symbol_table_ is
// set. symbol_table_initialized_ will be valid without symbol_table_ being
// set in modules that have no symbol table.
mutable InitializationState symbol_table_initialized_;
};
} // namespace crashpad
#endif // CRASHPAD_SNAPSHOT_MAC_MACH_O_IMAGE_READER_H_
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