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elf.cr
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elf.cr
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module Crystal
# :nodoc:
#
# ELF reader.
#
# Documentation:
# - <http://www.sco.com/developers/gabi/latest/contents.html>
struct ELF
MAGIC = UInt8.slice(0x7f, 'E'.ord, 'L'.ord, 'F'.ord)
enum Klass : UInt8
ELF32 = 1
ELF64 = 2
end
enum OSABI : UInt8
SYSTEM_V = 0x00
HP_UX = 0x01
NETBSD = 0x02
LINUX = 0x03
SOLARIS = 0x06
AIX = 0x07
IRIX = 0x08
FREEBSD = 0x09
OPENBSD = 0x0C
OPENVMS = 0x0D
NSK_OS = 0x0E
AROS = 0x0F
FENIS_OS = 0x10
CLOUDABI = 0x11
SORTIX = 0x53
end
enum Type : UInt16
REL = 1
EXEC = 2
DYN = 3
CORE = 4
end
enum Machine : UInt16
UNKNOWN = 0x00
SPARC = 0x02
X86 = 0x03
MIPS = 0x08
POWERPC = 0x14
ARM = 0x28
SUPERH = 0x2A
IA_64 = 0x32
X86_64 = 0x3E
AARCH64 = 0xB7
end
enum Endianness
Little = 1
Big = 2
end
struct Ident
property klass : Klass
property data : Endianness
property version : UInt8
property osabi : OSABI
property abiversion : UInt8
def initialize(@klass, @data, @version, @osabi, @abiversion)
end
end
struct SectionHeader
enum Type : UInt32
NULL = 0
PROGBITS = 1
SYMTAB = 2
STRTAB = 3
RELA = 4
HASH = 5
DYNAMIC = 6
NOTE = 7
NOBITS = 8
REL = 9
SHLIB = 10
DYNSYM = 11
INIT_ARRAY = 14
FINI_ARRAY = 15
PREINIT_ARRAY = 16
GROUP = 17
SYMTAB_SHNDX = 18
end
@[::Flags]
enum Flags : UInt64
WRITE = 0x1
ALLOC = 0x2
EXECINSTR = 0x4
MERGE = 0x10
STRINGS = 0x20
INFO_LINK = 0x40
LINK_ORDER = 0x80
OS_NONCONFORMING = 0x100
GROUP = 0x200
TLS = 0x400
COMPRESSED = 0x800
MASKOS = 0x0ff00000
MASKPROC = 0xf0000000
def short
String.build do |str|
str << 'W' if write?
str << 'A' if alloc?
str << 'X' if execinstr?
str << 'M' if merge?
str << 'S' if strings?
str << 'T' if tls?
end
end
end
property! name : UInt32
property! type : Type
property! flags : Flags
property! addr : UInt32 | UInt64
property! offset : UInt32 | UInt64
property! size : UInt32 | UInt64
property! link : UInt32
property! info : UInt32
property! addralign : UInt32 | UInt64
property! entsize : UInt32 | UInt64
end
class Error < Exception
end
getter! ident : Ident
property! type : Type
property! machine : Machine
property! version : UInt32
property! entry : UInt32 | UInt64
property! phoff : UInt32 | UInt64
property! shoff : UInt32 | UInt64
property! flags : UInt32
property! ehsize : UInt16
property! phentsize : UInt16
property! phnum : UInt16
property! shentsize : UInt16
property! shnum : UInt16
property! shstrndx : UInt16
def self.open(path)
File.open(path, "r") do |file|
yield new(file)
end
end
def initialize(@io : IO::FileDescriptor)
read_magic
read_ident
read_header
end
private def read_magic
@io.read(magic = Bytes.new(4))
if MAGIC.empty?
# If constant initialization is not working (for example when an
# error occurred during runtime setup or a custom main function doesn't
# do the initialization), continuing the ELF reader results in a
# seg fault. This condition detects the uninitialized constant and
# and errors.
# A simple program to reproduce is:
# ```
# module Crystal
# def self.main(&block)
# raise "foo"
# end
# end
# ```
Crystal::System.print_error "Error: %s\n", "Runtime is not initialized"
LibC.exit 1
end
raise Error.new("Invalid magic number") unless magic == MAGIC
end
private def read_ident
ei_class = Klass.new(@io.read_byte.not_nil!)
ei_data = Endianness.from_value(@io.read_byte.not_nil!)
ei_version = @io.read_byte.not_nil!
raise Error.new("Unsupported version number") unless ei_version == 1
ei_osabi = OSABI.from_value(@io.read_byte.not_nil!)
ei_abiversion = @io.read_byte.not_nil!
# padding (unused)
@io.skip(7)
@ident = Ident.new(ei_class, ei_data, ei_version, ei_osabi, ei_abiversion)
end
# Parses and returns an Array of `SectionHeader`.
def section_headers
@sections ||= Array(SectionHeader).new(shnum.to_i) do |i|
@io.seek(shoff + i * shentsize)
sh = SectionHeader.new
sh.name = read_word
sh.type = SectionHeader::Type.new(read_word)
sh.flags = SectionHeader::Flags.new(read_ulong.to_u64)
sh.addr = read_ulong
sh.offset = read_ulong
sh.size = read_ulong
sh.link = read_word
sh.info = read_word
sh.addralign = read_ulong
sh.entsize = read_ulong
sh
end
end
# Returns the name of a section, using the `SectionHeader#name` index.
def sh_name(index)
sh = section_headers[shstrndx]
@io.seek(sh.offset + index) do
@io.gets('\0', chomp: true).to_s
end
end
# Searches for a section then yield the `SectionHeader` and the IO object
# ready for parsing if the section was found. Returns the valure returned by
# the block or nil if the section wasn't found.
def read_section?(name : String)
if sh = section_headers.find { |sh| sh_name(sh.name) == name }
@io.seek(sh.offset) do
yield sh, @io
end
end
end
private def endianness
ident.data == Endianness::Little ? IO::ByteFormat::LittleEndian : IO::ByteFormat::BigEndian
end
private def read_word
@io.read_bytes(UInt32, endianness)
end
private def read_ulong
case ident.klass
when Klass::ELF32 then @io.read_bytes(UInt32, endianness)
when Klass::ELF64 then @io.read_bytes(UInt64, endianness)
else raise Error.new("Unsupported")
end
end
private def read_header
@type = Type.new(@io.read_bytes(UInt16, endianness).not_nil!)
@machine = Machine.new(@io.read_bytes(UInt16, endianness).not_nil!)
@version = @io.read_bytes(UInt32, endianness).not_nil!
raise Error.new("Unsupported version number") unless version == 1
@entry = read_ulong
@phoff = read_ulong
@shoff = read_ulong
@flags = @io.read_bytes(UInt32, endianness)
@ehsize = @io.read_bytes(UInt16, endianness)
case ident.klass
when Klass::ELF32
raise Error.new("Header should be 52 bytes for ELF32") unless ehsize == 52
when Klass::ELF64
raise Error.new("Header should be 64 bytes for ELF64") unless ehsize == 64
end
@phentsize = @io.read_bytes(UInt16, endianness)
@phnum = @io.read_bytes(UInt16, endianness)
@shentsize = @io.read_bytes(UInt16, endianness)
@shnum = @io.read_bytes(UInt16, endianness)
@shstrndx = @io.read_bytes(UInt16, endianness)
end
end
end