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Optimize ELF parser
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@ntkme
ntkme committed Aug 3, 2024
1 parent c3b1cf0 commit 35a6f26
Showing 1 changed file with 99 additions and 116 deletions.
215 changes: 99 additions & 116 deletions lib/sass/elf.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -7,24 +7,49 @@ module Sass
# @see https://github.com/torvalds/linux/blob/HEAD/include/uapi/linux/elf.h
# @see https://github.com/torvalds/linux/blob/HEAD/kernel/kexec_elf.c
class ELF
module PackInfo
PACK_MAP = {
U8: 'C',
S8: 'c',
u16: 'S<',
U16: 'S>',
s16: 's<',
S16: 's>',
u32: 'L<',
U32: 'L>',
s32: 'l<',
S32: 'l>',
u64: 'Q<',
U64: 'Q>',
s64: 'q<',
S64: 'q>'
}.freeze

SIZE_MAP = PACK_MAP.to_h do |type, _|
[type, type.to_s[1..].to_i / 8]
end.freeze
end

private_constant :PackInfo

# rubocop:disable Naming/ConstantName

# 32-bit ELF base types.
Elf32_Addr = :__u32
Elf32_Half = :__u16
Elf32_Off = :__u32
Elf32_Sword = :__s32
Elf32_Word = :__u32
Elf32_Addr = :u32
Elf32_Half = :u16
Elf32_Off = :u32
Elf32_Sword = :s32
Elf32_Word = :u32

# 64-bit ELF base types.
Elf64_Addr = :__u64
Elf64_Half = :__u16
Elf64_SHalf = :__s16
Elf64_Off = :__u64
Elf64_Sword = :__s32
Elf64_Word = :__u32
Elf64_Xword = :__u64
Elf64_Sxword = :__s64
Elf64_Addr = :u64
Elf64_Half = :u16
Elf64_SHalf = :s16
Elf64_Off = :u64
Elf64_Sword = :s32
Elf64_Word = :u32
Elf64_Xword = :u64
Elf64_Sxword = :s64

# rubocop:enable Naming/ConstantName

Expand All @@ -41,10 +66,6 @@ class ELF
PT_HIOS = 0x6fffffff
PT_LOPROC = 0x70000000
PT_HIPROC = 0x7fffffff
PT_GNU_EH_FRAME = (PT_LOOS + 0x474e550)
PT_GNU_STACK = (PT_LOOS + 0x474e551)
PT_GNU_RELRO = (PT_LOOS + 0x474e552)
PT_GNU_PROPERTY = (PT_LOOS + 0x474e553)

# These constants define the different elf file types
ET_NONE = 0
Expand All @@ -60,37 +81,37 @@ class ELF
# rubocop:disable Naming/ConstantName

Elf32_Ehdr = [
[:unsigned_char, :e_ident, EI_NIDENT],
[Elf32_Half, :e_type],
[Elf32_Half, :e_machine],
[Elf32_Word, :e_version],
[Elf32_Addr, :e_entry],
[Elf32_Off, :e_phoff],
[Elf32_Off, :e_shoff],
[Elf32_Word, :e_flags],
[Elf32_Half, :e_ehsize],
[Elf32_Half, :e_phentsize],
[Elf32_Half, :e_phnum],
[Elf32_Half, :e_shentsize],
[Elf32_Half, :e_shnum],
[Elf32_Half, :e_shstrndx]
[:U8, :e_ident, EI_NIDENT],
[Elf32_Half, :e_type],
[Elf32_Half, :e_machine],
[Elf32_Word, :e_version],
[Elf32_Addr, :e_entry],
[Elf32_Off, :e_phoff],
[Elf32_Off, :e_shoff],
[Elf32_Word, :e_flags],
[Elf32_Half, :e_ehsize],
[Elf32_Half, :e_phentsize],
[Elf32_Half, :e_phnum],
[Elf32_Half, :e_shentsize],
[Elf32_Half, :e_shnum],
[Elf32_Half, :e_shstrndx]
].freeze

Elf64_Ehdr = [
[:unsigned_char, :e_ident, EI_NIDENT],
[Elf64_Half, :e_type],
[Elf64_Half, :e_machine],
[Elf64_Word, :e_version],
[Elf64_Addr, :e_entry],
[Elf64_Off, :e_phoff],
[Elf64_Off, :e_shoff],
[Elf64_Word, :e_flags],
[Elf64_Half, :e_ehsize],
[Elf64_Half, :e_phentsize],
[Elf64_Half, :e_phnum],
[Elf64_Half, :e_shentsize],
[Elf64_Half, :e_shnum],
[Elf64_Half, :e_shstrndx]
[:U8, :e_ident, EI_NIDENT],
[Elf64_Half, :e_type],
[Elf64_Half, :e_machine],
[Elf64_Word, :e_version],
[Elf64_Addr, :e_entry],
[Elf64_Off, :e_phoff],
[Elf64_Off, :e_shoff],
[Elf64_Word, :e_flags],
[Elf64_Half, :e_ehsize],
[Elf64_Half, :e_phentsize],
[Elf64_Half, :e_phnum],
[Elf64_Half, :e_shentsize],
[Elf64_Half, :e_shnum],
[Elf64_Half, :e_shstrndx]
].freeze

Elf32_Phdr = [
Expand Down Expand Up @@ -149,10 +170,39 @@ class ELF

def initialize(buffer)
@buffer = buffer
@ehdr = read_ehdr

@ehdr = { e_ident: @buffer.read(EI_NIDENT).unpack('C*') }
raise ArgumentError unless @ehdr[:e_ident].slice(EI_MAG0, SELFMAG).pack('C*') == ELFMAG

case @ehdr[:e_ident][EI_CLASS]
when ELFCLASS32
elf_ehdr = Elf32_Ehdr
elf_phdr = Elf32_Phdr
when ELFCLASS64
elf_ehdr = Elf64_Ehdr
elf_phdr = Elf64_Phdr
else
raise ArgumentError
end

case @ehdr[:e_ident][EI_DATA]
when ELFDATA2LSB
little_endian = true
when ELFDATA2MSB
little_endian = false
else
raise ArgumentError
end

elf_ehdr.drop(1).each do |type, name|
@ehdr[name] = read1(type, little_endian)
end

@buffer.seek(@ehdr[:e_phoff], IO::SEEK_SET)
@proghdrs = Array.new(@ehdr[:e_phnum]) do
read_phdr
elf_phdr.to_h do |type, name|
[name, read1(type, little_endian)]
end
end
end

Expand Down Expand Up @@ -185,75 +235,8 @@ def interpreter

private

def file_class
@ehdr[:e_ident][EI_CLASS]
end

def data_encoding
@ehdr[:e_ident][EI_DATA]
end

def read_ehdr
@ehdr = { e_ident: @buffer.read(EI_NIDENT).unpack('C*') }
raise ArgumentError unless @ehdr[:e_ident].slice(EI_MAG0, SELFMAG).pack('C*') == ELFMAG

case file_class
when ELFCLASS32
Elf32_Ehdr
when ELFCLASS64
Elf64_Ehdr
else
raise ArgumentError
end.drop(1).to_h do |field|
[field[1], read1(field[0])]
end.merge!(@ehdr)
end

def read_phdr
case file_class
when ELFCLASS32
Elf32_Phdr
when ELFCLASS64
Elf64_Phdr
else
raise ArgumentError
end.to_h do |field|
[field[1], read1(field[0])]
end
end

def explicit_endian
case data_encoding
when ELFDATA2LSB
'<'
when ELFDATA2MSB
'>'
else
raise ArgumentError
end
end

def read1(type)
case type
when :__u8
@buffer.read(1).unpack1('C')
when :__u16
@buffer.read(2).unpack1("S#{explicit_endian}")
when :__u32
@buffer.read(4).unpack1("L#{explicit_endian}")
when :__u64
@buffer.read(8).unpack1("Q#{explicit_endian}")
when :__s8
@buffer.read(1).unpack1('c')
when :__s16
@buffer.read(2).unpack1("s#{explicit_endian}")
when :__s32
@buffer.read(4).unpack1("l#{explicit_endian}")
when :__s64
@buffer.read(8).unpack1("q#{explicit_endian}")
else
raise ArgumentError
end
def read1(type, little_endian)
@buffer.read(PackInfo::SIZE_MAP[type]).unpack1(PackInfo::PACK_MAP[little_endian ? type : type.upcase])
end

INTERPRETER = begin
Expand Down

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