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Mikhail Chupilko, 04/06/2017 06:05 pm


Getting Started with x86

Prerequisite

MicroTESK should be installed.

Demo Specifications

Specifications of the x86 (8086) instruction set architecture (ISA) can be found in $MICROTESK_HOME/arch/demo/x86/model/x86.nml.

Instruction are described in nML by means of the following constructs (mov r16/r16 is taken as an example):

  1. the signature
    op mov_r1616 (dst: GPR16, src: GPR16)
  2. the assembly format
    syntax = format("mov %s, %s", dst.syntax, src.syntax)
  3. the binary encoding
    image = format("1000101111%s%s", dst.image, src.image)
  4. the semantics
      action = {
        dst = src;
        ...
      }
    

To compile the ISA model, run the following command:

sh $MICROTESK_HOME/bin/compile.sh x86.nml

Demo Templates

Test templates for the x86 ISA can be found in $MICROTESK_HOME/arch/demo/x86/templates.

The directory contains a number of demo templates including the following ones:

block.rb demonstrates how to use block constructs
block_random.rb demonstrates how to create randomized instruction sequences using block constructs
euclid.rb demonstrates test program simulation to predict the resulting microprocessor state
random.rb demonstrates how to randomize tests by using biases and distributions
random_immediate.rb demonstrates how to randomize immediate values
random_registers.rb demonstrates how to randomize registers (dependencies)

Test templates are written in Ruby extended with specific constructs.

Let's review one of the templates (block.rb) in detail.
  1. includes the file where the base class is defined, containing definition of the x86 ISA registers, their preparators, etc.
    require_relative 'x86_base'
  2. declares current template class declaration as a heir of X86BaseTemplate
    class BlockTemplate < X86BaseTemplate
  3. defines a "run" method (also, "initialize", "pre", and "post" methods are declared in the base class, and always inherited)
    def run
  4. produces a single test case that consists of three instructions
      sequence {
        mov_r16r16 ax, bx
        sub_r16r16 cx, dx
        add_r16r16 gpr16(_), gpr16(_)
      }.run
    
  5. atomic sequence; works as sequence in this context
      atomic {
        mov_r16r16 ax, bx
        add_r16r16 cx, dx
        sub_r16r16 gpr16(_), gpr16(_)
      }.run
    
  6. produces three test cases each consisting of one instruction
      iterate {
        mov_r16r16 ax, bx
        sub_r16r16 cx, dx
        add_r16r16 gpr16(_), gpr16(_)
      }.run
    
  7. produces four test cases consisting of two instructions (Cartesian product composed in a random order)
      block(:combinator => 'product', :compositor => 'random') {
        iterate {
          sub_r16r16 cx, dx
          add_r16r16 ax, bx
        }
        iterate {
          mov_r16r16 ax, bx
          sub_r16r16 gpr16(_), gpr16(_)
        }
      }.run
    
  8. merges two sequences in random fashion; atomic sequences are unmodifiable
      block(:combinator => 'diagonal', :compositor => 'random', :obfuscator => 'random') {
        sequence {
          sub_r16r16 bx, ax
          or_r16r16 cx, dx
        }
    
        atomic {
          prologue { comment 'Atomic starts' }
          epilogue { comment 'Atomic ends' }
    
          and_r16r16 gpr16(_), gpr16(_)
        }
      }.run
    
  9. finishes definition of the "run" method and class "BlockTemplate"
     end
    end
    

To generate test program(s) from a test template (in our case, from block.rb), run the following command:

sh $MICROTESK_HOME/bin/generate.sh x86 block.rb --code-file-prefix block --code-file-extension s -v

When generation is finished, the resulting assembly code can be found in $MICROTESK_HOME.

To compile the output file, run the following commands:

nasm -f elf block_0000.s
ld -m i386pe -s -o block_0000 block_0000.o

To execute resulted test cases is possible by means of the online simulator

Example_block.png (92.3 KB) Mikhail Chupilko, 04/06/2017 05:40 pm

block_0000.s (3.12 KB) Alexander Protsenko, 04/06/2017 05:55 pm