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Merged
katsyoshi merged 2 commits into from
Jan 24, 2026
Merged

support ET_DYN output in self linker #34

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1879249
support ET_DYN output in self linker
katsyoshi Jan 24, 2026
dd02a7b
add test for shared object link
katsyoshi Jan 24, 2026
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39 changes: 13 additions & 26 deletions lib/caotral/binary/elf/header.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -7,11 +7,16 @@ class Header
IDENT = [0x7f, 0x45, 0x4c, 0x46, 0x02, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00].freeze
IDENT_STR = IDENT.pack("C*").freeze
ELF_FILE_TYPE = { NONE: 0, REL: 1, EXEC: 2, DYN: 3, CORE: 4 }.freeze
ELF_TARGET_MACHINE = { AMD64: 62 }.freeze
TYPE = ELF_FILE_TYPE
ITYPE = TYPE.invert.freeze
MACHINE = ELF_TARGET_MACHINE
IMACHINE = MACHINE.invert.freeze

def initialize(endian: :little, type: :rel, arc: :amd64)
def initialize(endian: :little, type: :REL)
@ident = IDENT
@type = num2bytes(ELF_FILE_TYPE[elf(type)], 2)
@arch = arch(arc)
@type = num2bytes(ELF_FILE_TYPE[type], 2)
@arch = num2bytes(62, 2) # target: e_machine EM_x86_64
Comment on lines +16 to +19
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@chatgpt-codex-connector chatgpt-codex-connector bot Jan 24, 2026

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P2 Badge Preserve Header.new keyword/type normalization

The initializer now directly indexes ELF_FILE_TYPE[type] and dropped the previous normalization logic, so callers that still pass type: :rel/:exec or string values (which were accepted before) will now hit nil and raise a TypeError inside num2bytes. Also, removing the arc: keyword means any existing caller supplying arc: now gets an ArgumentError. This is a runtime regression for existing usage patterns; consider keeping the normalization/keyword or raising a clearer validation error.

Useful? React with 👍 / 👎.

@version = num2bytes(1, 4)
@entry = num2bytes(0x00, 8)
@phoffset = num2bytes(0x00, 8)
Expand All @@ -27,8 +32,9 @@ def initialize(endian: :little, type: :rel, arc: :amd64)

def build = bytes.flatten.pack("C*")

def set!(type: nil, entry: nil, phoffset: nil, shoffset: nil, shnum: nil, shstrndx: nil, phsize: nil, phnum: nil, ehsize: nil)
def set!(type: nil, arch: nil, entry: nil, phoffset: nil, shoffset: nil, shnum: nil, shstrndx: nil, phsize: nil, phnum: nil, ehsize: nil)
@type = num2bytes(type, 2) if check(type, 2)
@arch = num2bytes(arch, 2) if check(arch, 2)
@entry = num2bytes(entry, 8) if check(entry, 8)
@phoffset = num2bytes(phoffset, 8) if check(phoffset, 8)
@phsize = num2bytes(phsize, 2) if check(phsize, 2)
Expand All @@ -48,33 +54,14 @@ def shentsize = @shentsize.pack("C*").unpack1("S<")
def shnum = @shnum.pack("C*").unpack1("S<")
def shstrndx = @shstrndx.pack("C*").unpack1("S<")
def shoffset = @shoffset.pack("C*").unpack1("Q<")
def type = ITYPE[@type.pack("C*").unpack1("S<")]
def arch = IMACHINE[@arch.pack("C*").unpack1("S<")]

private
def bytes = [
private def bytes = [
@ident, @type, @arch, @version, @entry, @phoffset,
@shoffset, @flags, @ehsize, @phsize, @phnum, @shentsize,
@shnum, @shstrndx
]

def arch(machine)
case machine.to_s
in "amd64" | "x86_64" | "x64"
[0x3e, 0x00]
end
end

def elf(type)
case type.to_s
in "relocatable" | "rel"
:REL
in "exe" | "ex" | "exec"
:EXEC
in "shared" | "share" | "dynamic" | "dyn"
:DYN
else
:NONE
end
end
end
end
end
Expand Down
18 changes: 10 additions & 8 deletions lib/caotral/binary/elf/reader.rb
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Expand Up @@ -18,14 +18,16 @@ def read
header = @bin.read(0x40)
ident = header[0, 16]
raise "Not ELF file" unless ident == Caotral::Binary::ELF::Header::IDENT_STR

entry = header[24, 8].unpack("Q<").first
phoffset = header[32, 8].unpack("Q<").first
shoffset = header[40, 8].unpack("Q<").first
shentsize = header[58, 2].unpack("S<").first
shnum = header[60, 2].unpack("S<").first
shstrndx = header[62, 2].unpack("S<").first
@context.header.set!(entry:, phoffset:, shoffset:, shnum:, shstrndx:)

type = header[16, 2].unpack1("S<")
arch = header[18, 2].unpack1("S<")
entry = header[24, 8].unpack1("Q<")
phoffset = header[32, 8].unpack1("Q<")
shoffset = header[40, 8].unpack1("Q<")
shentsize = header[58, 2].unpack1("S<")
shnum = header[60, 2].unpack1("S<")
shstrndx = header[62, 2].unpack1("S<")
@context.header.set!(type:, arch:, entry:, phoffset:, shoffset:, shnum:, shstrndx:)

@bin.pos = shoffset
shnum.times do |i|
Expand Down
14 changes: 10 additions & 4 deletions lib/caotral/linker/builder.rb
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Expand Up @@ -12,12 +12,13 @@ class Builder
RELOCATION_SECTION_NAMES = [".rela.text", ".rel.text"].freeze
ALLOW_RELOCATION_TYPES = [R_X86_64_PC32, R_X86_64_PLT32].freeze

attr_reader :symbols, :executable, :debug
attr_reader :symbols

def initialize(elf_objs:, executable: true, debug: false, shared: false)
@elf_objs = elf_objs
@executable, @debug, @shared = executable, debug, shared
@symbols = { locals: Set.new, globals: Set.new, weaks: Set.new }
sharing_object!
end

def build
Expand Down Expand Up @@ -52,6 +53,10 @@ def build
start_bytes = [0xe8, *[0] * 4, 0x48, 0x89, 0xc7, 0x48, 0xc7, 0xc0, 0x3c, 0x00, 0x00, 0x00, 0x0f, 0x05]
exec_text_offset = 0x1000
base_addr = 0x400000
unless @executable
start_bytes = []
base_addr = 0
end
vaddr = base_addr + exec_text_offset
start_len = start_bytes.length
sections = []
Expand Down Expand Up @@ -108,9 +113,9 @@ def build
sections << null_section

main_sym = symtab_section.body.find { |sym| sym.name_string == "main" }
raise Caotral::Binary::ELF::Error, "main function not found" if executable && main_sym.nil?
raise Caotral::Binary::ELF::Error, "main function not found" if @executable && main_sym.nil?
main_offset = main_sym.nil? ? 0 : main_sym.value + start_len
start_bytes[1, 4] = num2bytes((main_offset - 5), 4)
start_bytes[1, 4] = num2bytes((main_offset - 5), 4) if @executable
text_section.body.prepend(start_bytes.pack("C*"))

text_section.header.set!(
Expand Down Expand Up @@ -226,7 +231,7 @@ def build
target.body = bytes
end

sections = sections.reject { |section| RELOCATION_SECTION_NAMES.any? { |name| name === section.section_name.to_s } } if executable
sections = sections.reject { |section| RELOCATION_SECTION_NAMES.any? { |name| name === section.section_name.to_s } } if @executable
sections.each { |section| elf.sections << section }

elf
Expand Down Expand Up @@ -258,6 +263,7 @@ def ref_index(sections, section_name)

def rel_type(section) = section.section_name&.start_with?(".rela.") ? 4 : 9
def rel_entsize(section) = section.section_name&.start_with?(".rela.") ? 24 : 16
def sharing_object! = (@executable = false if @shared)
end
end
end
9 changes: 7 additions & 2 deletions lib/caotral/linker/writer.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -16,10 +16,14 @@ def initialize(elf_obj:, output:, entry: nil, debug: false, executable: true, sh
@elf_obj, @output, @entry, @debug, @executable, @shared = elf_obj, output, entry, debug, executable, shared
@write_sections = write_order_sections
end

def write
f = File.open(@output, "wb")
phoffset, phnum, phsize, ehsize = 64, 1, 56, 64
header = @elf_obj.header.set!(type: 2, phoffset:, phnum:, phsize:, ehsize:)
file_type = @shared ? :DYN : :EXEC
e_type = Caotral::Binary::ELF::Header::TYPE[file_type]

header = @elf_obj.header.set!(type: e_type, phoffset:, phnum:, phsize:, ehsize:)
ph = Caotral::Binary::ELF::ProgramHeader.new
text_offset = text_section.header.offset
align = 0x1000
Expand All @@ -28,8 +32,9 @@ def write
type, flags = 1, 5
filesz = text_section.body.bytesize
memsz = filesz
entry = @shared ? 0 : (@entry || vaddr)

header.set!(entry: @entry || vaddr)
header.set!(entry:)
ph.set!(type:, offset: text_offset, vaddr:, paddr:, filesz:, memsz:, flags:, align:)
f.write(@elf_obj.header.build)
f.write(ph.build)
Expand Down
1 change: 1 addition & 0 deletions sample/C/shared-object.c
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
int foo() { return 42; }
23 changes: 23 additions & 0 deletions test/caotral/linker/shared-object_test.rb
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@@ -0,0 +1,23 @@
require_relative "../../test_suite"

class Caotral::Linker::SharedObjectLinkingTest < Test::Unit::TestCase
include TestProcessHelper
def setup
@inputs = ["shared.o"]
@output = "libshared.so"
path = Pathname.new("sample/C/shared-object.c").to_s
IO.popen(["gcc", "-fPIC", "-c", "-o", @inputs[0], "%s" % path]).close
end

def teardown
File.delete(@inputs[0]) if File.exist?(@inputs[0])
File.delete(@output) if File.exist?(@output)
end

def test_link_shared_object
Caotral::Linker.link!(inputs: @inputs, output: @output, linker: "self", shared: true, executable: false)
elf = Caotral::Binary::ELF::Reader.read!(input: @output, debug: false)
assert_equal(:DYN, elf.header.type)
assert_equal(:AMD64, elf.header.arch)
end
end