Implement mov encoding properly

lib/mjit/insn_compiler.rb

@@ -1,17 +1,17 @@
 module RubyVM::MJIT
   class InsnCompiler
-    def on_putnil(_asm)
+    def putnil(_asm)
       # TODO
       KeepCompiling
     end
 
-    def on_leave(asm)
+    def leave(asm)
       # pop the current frame (ec->cfp++)
       asm.add(:rsi, C.rb_control_frame_t.size)
       asm.mov([:rdi, C.rb_execution_context_t.offsetof(:cfp)], :rsi)
 
       # return a value
-      asm.mov(:rax, 7)
+      asm.mov(:rax, 1001)
       asm.ret
       EndBlock
     end

lib/mjit/x86_assembler.rb

@@ -1,7 +1,13 @@
+# frozen_string_literal: true
+# https://www.intel.com/content/dam/develop/public/us/en/documents/325383-sdm-vol-2abcd.pdf
 module RubyVM::MJIT
   class X86Assembler
     ByteWriter = CType::Immediate.parse('char')
 
+    ### prefix ###
+    # REX =   0100WR0B
+    REX_W = 0b01001000
+
     def initialize
       @bytes = []
     end
@@ -23,21 +29,114 @@ module RubyVM::MJIT
       @bytes.push(0x48, 0x83, 0xc6, imm)
     end
 
-    def mov(reg, val)
-      case reg
-      when :rax
-        #           REX.W [C7]  RAX   imm32
-        @bytes.push(0x48, 0xc7, 0xc0, val, 0x00, 0x00, 0x00)
+    def mov(dst, src)
+      case [dst, src]
+      # MOV r/m64, imm32
+      in [Symbol => dst_reg, Integer => src_imm] if r_reg?(dst_reg)
+        # REX.W + C7 /0
+        insn(
+          prefix: REX_W,
+          opcode: 0xc7,
+          mod_rm: mod_rm(mod: 0b11, reg: reg_code(dst_reg)),
+          imm: imm32(src_imm),
+        )
+      # MOV r/m64, r64
+      in [[Symbol => dst_reg, Integer => dst_offset], Symbol => src_reg] if r_reg?(dst_reg) && r_reg?(src_reg) && dst_offset <= 0xff
+        # REX.W + 89 /r
+        insn(
+          prefix: REX_W,
+          opcode: 0x89,
+          mod_rm: mod_rm(mod: 0b01, reg: reg_code(src_reg), rm: reg_code(dst_reg)), # disp8
+          disp: dst_offset,
+        )
       else
-        #           REX.W [89]  [rdi+val],rsi
-        @bytes.push(0x48, 0x89, 0x77, reg.last)
+        raise NotImplementedError, "mov got not-implemented input: #{reg.inspect}, #{val.inspect}"
       end
     end
 
+    # RET
     def ret
-      # Near return
-      #           [C3]
-      @bytes.push(0xc3)
+      # Near return: A return to a procedure within the current code segment
+      insn(opcode: 0xc3)
+    end
+
+    private
+
+    def insn(prefix: nil, opcode:, mod_rm: nil, disp: nil, imm: nil)
+      if prefix
+        @bytes.push(prefix)
+      end
+      @bytes.push(opcode)
+      if mod_rm
+        @bytes.push(mod_rm)
+      end
+      if disp
+        if disp < 0 || disp > 0xff # TODO: support displacement in 2 or 4 bytes as well
+          raise NotImplementedError, "not-implemented disp: #{disp}"
+        end
+        @bytes.push(disp)
+      end
+      if imm
+        @bytes.push(*imm)
+      end
+    end
+
+    def reg_code(reg)
+      case reg
+      when :al, :ax, :eax, :rax then 0
+      when :cl, :cx, :ecx, :rcx then 1
+      when :dl, :dx, :edx, :rdx then 2
+      when :bl, :bx, :ebx, :rbx then 3
+      when :ah, :sp, :esp, :rsp then 4
+      when :ch, :bp, :ebp, :rbp then 5
+      when :dh, :si, :esi, :rsi then 6
+      when :bh, :di, :edi, :rdi then 7
+      else raise ArgumentError, "unexpected reg: #{reg.inspect}"
+      end
+    end
+
+    # Table 2-2. 32-Bit Addressing Forms with the ModR/M Byte
+    #
+    #  7  6  5  4  3  2  1  0
+    # +--+--+--+--+--+--+--+--+
+    # | Mod | Reg/   | R/M    |
+    # |     | Opcode |        |
+    # +--+--+--+--+--+--+--+--+
+    #
+    # The r/m field can specify a register as an operand or it can be combined
+    # with the mod field to encode an addressing mode.
+    #
+    # /0: R/M is 0 (not used)
+    # /r: R/M is a register
+    def mod_rm(mod:, reg:, rm: 0)
+      if mod > 0b11
+        raise ArgumentError, "too large Mod: #{mod}"
+      end
+      if reg > 0b111
+        raise ArgumentError, "too large Reg/Opcode: #{reg}"
+      end
+      if rm > 0b111
+        raise ArgumentError, "too large R/M: #{rm}"
+      end
+      (mod << 6) + (reg << 3) + rm
+    end
+
+    # id: 4 bytes
+    def imm32(imm)
+      bytes = []
+      bits = imm
+      4.times do
+        bytes << (bits & 0xff)
+        bits >>= 8
+      end
+      if bits != 0
+        raise ArgumentError, "unexpected imm32: #{imm}"
+      end
+      bytes
+    end
+
+    def r_reg?(reg)
+      reg.start_with?('r')
     end
   end
 end

lib/ruby_vm/mjit/compiler.rb

@@ -26,8 +26,7 @@ module RubyVM::MJIT
       return if iseq.body.location.label == '<main>'
       iseq.body.jit_func = compile_block(iseq)
     rescue Exception => e
-      # TODO: check --mjit-verbose
-      $stderr.puts e.full_message
+      $stderr.puts e.full_message # TODO: check verbose
     end
 
     def write_addr
@@ -36,6 +35,20 @@ module RubyVM::MJIT
 
     private
 
+    def compile(asm)
+      start_addr = write_addr
+
+      C.mjit_mark_writable
+      @write_pos += asm.compile(start_addr)
+      C.mjit_mark_executable
+
+      end_addr = write_addr
+      if C.mjit_opts.dump_disasm && start_addr < end_addr
+        dump_disasm(start_addr, end_addr)
+      end
+      start_addr
+    end
+
     # ec -> RDI, cfp -> RSI
     def compile_block(iseq)
       addr = write_addr
@@ -56,26 +69,12 @@ module RubyVM::MJIT
 
     def compile_insn(asm, insn)
       case insn.name
-      when :putnil then @insn_compiler.on_putnil(asm)
-      when :leave  then @insn_compiler.on_leave(asm)
+      when :putnil then @insn_compiler.putnil(asm)
+      when :leave  then @insn_compiler.leave(asm)
       else raise NotImplementedError, "insn '#{insn.name}' is not supported yet"
       end
     end
 
-    def compile(asm)
-      start_addr = write_addr
-
-      C.mjit_mark_writable
-      @write_pos += asm.compile(start_addr)
-      C.mjit_mark_executable
-
-      end_addr = write_addr
-      if C.mjit_opts.dump_disasm && start_addr < end_addr
-        dump_disasm(start_addr, end_addr)
-      end
-      start_addr
-    end
-
     def decode_insn(encoded)
       INSNS.fetch(C.rb_vm_insn_decode(encoded))
     end