Optimize ELF parser

sass-contrib · Aug 1, 2024 · b3c8fa6 · b3c8fa6
1 parent c3b1cf0
commit b3c8fa6
Showing 1 changed file with 50 additions and 55 deletions.
diff --git a/lib/sass/elf.rb b/lib/sass/elf.rb
@@ -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
 
@@ -60,7 +85,7 @@ class ELF
     # rubocop:disable Naming/ConstantName
 
     Elf32_Ehdr = [
-      [:unsigned_char, :e_ident, EI_NIDENT],
+      [:U8,            :e_ident, EI_NIDENT],
       [Elf32_Half,     :e_type],
       [Elf32_Half,     :e_machine],
       [Elf32_Word,     :e_version],
@@ -77,7 +102,7 @@ class ELF
     ].freeze
 
     Elf64_Ehdr = [
-      [:unsigned_char, :e_ident, EI_NIDENT],
+      [:U8,            :e_ident, EI_NIDENT],
       [Elf64_Half,     :e_type],
       [Elf64_Half,     :e_machine],
       [Elf64_Word,     :e_version],
@@ -185,32 +210,25 @@ 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
+      case @ehdr[:e_ident][EI_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.drop(1).each do |field|
+        @ehdr[field[1]] = read1(field[0])
+      end
+      @ehdr
     end
 
     def read_phdr
-      case file_class
+      case @ehdr[:e_ident][EI_CLASS]
       when ELFCLASS32
         Elf32_Phdr
       when ELFCLASS64
@@ -222,35 +240,12 @@ def read_phdr
       end
     end
 
-    def explicit_endian
-      case data_encoding
+    def read1(type)
+      case @ehdr[:e_ident][EI_DATA]
       when ELFDATA2LSB
-        '<'
+        @buffer.read(PackInfo::SIZE_MAP[type]).unpack1(PackInfo::PACK_MAP[type])
       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}")
+        @buffer.read(PackInfo::SIZE_MAP[type]).unpack1(PackInfo::PACK_MAP[type.upcase])
       else
         raise ArgumentError
       end