tree: 7dc4ca1fa58deb3c94a79e5e82670ae997b41292 [path history] [tgz]
  1. BUILD.gn
  2. README.md
  3. field-tests.cc
  4. include/
  5. layout-tests.cc
src/lib/elfldltl/README.md

ELF Loading & Dynamic Linking Template Library (elfldltl)

This library provides a toolkit of C++ template APIs for implementing ELF dynamic linking and loading functionality. It uses C++ namespace elfldltl.

The library API supports either 32-bit or 64-bit ELF with either little-endian or big-endian byte order, via template parameters. Thus it is suitable for cross-tools without assumptions about host machine or operating system details, as well as for ELF target build environments of various sorts.

Format layouts and constants

The library provides the ELF format layouts and constants in a modern C++ API using canonical style. It does not intend to be an exhaustive API for all of the ELF format. It provides the full range of data structures and constants used in dynamic linking and loading, and some others that are of use in related tools. It does not provide full details needed for compilers, linkers, debuggers, etc. In some instances it defines all constants of a particular type, while in others it defines only the subset actually used or supported by the toolkit. It provides details from the formal ELF specification and for de facto standard GNU and LLVM extensions on the same footing. The constants and data structures largely mimic the spellings used in the ELF specification, which come from the traditional <elf.h> C API. However, these definitions use C++ scoping and canonical identifier styles that do not overlap with it.

The generic ELF format constants are defined in <lib/elfldltl/constants.h>. These are mostly enum class types that apply to all format variants and machines. Types selecting format variant and machine also include convenient kNative aliases for the native platform being compiled for.

ELF data layouts are defined in <lib/elfldltl/layout.h>. These are provided as C++ struct types within the elfldltl::Elf template class, which is parameterized by class (32-bit vs 64-bit) and data format (byte order) with default template arguments matching the native platform being compiled for.

Field accessors

ELF format data types are defined using a simple set of generic wrapper template types for defining fields, defined in <lib/elfldltl/field.h>. This API can also be used directly for other data structures in ELF sections or in memory for which doing access across bit widths and/or byte orders may be useful.

The wrapper types used for fields have the same exact ABI layout as a specified underlying integer type. Their API behavior as C++ objects is roughly like a normal field of a given integer or enum type, in that they are implicitly convertible to and from that type and can be compared to it for equality. In contexts where the C++ type is flexible, these implicit conversions may not be sufficient and these objects do not fully emulate an integer or enum type. So they also provide direct accessor methods via field.get() or field() (i.e. calling the field as a function of no arguments).