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updated README
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Sami Samhuri
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README.md
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README.md
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@ -2,7 +2,7 @@ sjs<br>
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[sami.samhuri@gmail.com](mailto:sami.samhuri@gmail.com)<br>
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published : 2009-09-22<br>
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updated : 2009-09-24
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updated : 2010-01-19
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Overview
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@ -13,91 +13,81 @@ on the tutorial "Let's Build a Compiler" by Jack Crenshaw[1].
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[1]: http://compilers.iecc.com/crenshaw/
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The semantics are simple and familiar to all programmers. Eager
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The semantics are simple and familiar to most programmers. Eager
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evaluation, assignment with the equals sign, arithmetic using + - *
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and /, loops, if/else statement, etc. Integers are the only data type.
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and /, loops, if/else statement, etc. Integers are the only data
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type.
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While the parser still closely resembles Crenshaw's recursive descent
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parser, back-end generates x85 machine code using a homegrown
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assembler in ~1000 lines of Ruby (just 650 lines of real code).
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NOTE: OS X is the only platform that compiles working binaries right
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now. ELF support for Linux coming soon.
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now. ELF support for Linux coming ... eventually.
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Compiling
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========
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Pre-requisites
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==============
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OS X
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----
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You need gcc, so install Xcode or use MacPorts to build gcc.
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You need Ruby and gcc. Ruby is standard on Macs but you'll need to
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install Xcode for gcc. You can also compile it yourself or use
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MacPorts, or [homebrew](http://github.com/mxcl/homebrew).
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Linux
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-----
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You need ruby and ld which lives in the binutils package.
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You need Ruby and ld - which lives in the binutils package.
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% sudo aptitude install ruby binutils
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That's it! The assembler is included in ~900 lines of Ruby (including
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comments).
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That's it!
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You should be fine letting the build script detect your platform. If
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not append 'elf' or 'macho' to the command.
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Compiling
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=========
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The build script should detect your platform. If not append 'elf' or
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'macho' to the command.
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% ./build.rb filename.code [elf | macho]
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The resulting native executable will be called 'filename' and you
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should be able to run it directly.
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% ./filename <return>
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The resulting native executable is called 'filename' and you should be
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able it run it directly.
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% ./filename
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Syntax in 2 minutes
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===================
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The recursive descent parser starts by parsing a block of code. A
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block consists of zero or more statements. Whitespace is largely
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ignored beyond delimiting tokens so statements can be grouped on one
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line or spread out over multiple lines. With no explicit terminator
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this can look strange so we will see how it works out when the syntax
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evolves into something more complicated.
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The parser starts by parsing a block of code. A block consists of one
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or more statements. Whitespace is largely ignored beyond delimiting
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tokens, so statements can be grouped on one line or spread out over
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multiple lines. With no explicit terminator this can look strange so
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we will see how it works out when the syntax evolves into something
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more complicated.
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There are no functions or function calls, no closures, arrays, hashes,
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or anything else you can think of.
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There are variables and integers. That's honestly about it. There
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are no functions or function calls, no closures, arrays, hashes, or
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anything else.
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Supported statements are:
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* assignment
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e.g. foo = 4096
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* if/else
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e.g. if x < 0 a=0 else a=1 end
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* while
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e.g. while x > 0 x=x-1 end
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* until
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e.g. until x == 0 x=x-1 end
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* break
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e.g. break
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* repeat
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e.g. repeat x=x-1 if x == 0 break end end
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* for
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e.g. for i=1 to 5 x=x+1 end
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* do
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e.g. do 5 x=x+1 end
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* print
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e.g. a=1 print
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* assignment<br> e.g. foo = 4096
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* if/else<br> e.g. if x < 0 a=0 else a=1 end
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* while<br> e.g. while x > 0 x=x-1 end
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* until<br> e.g. until x == 0 x=x-1 end
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* break<br> e.g. break
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* repeat<br> e.g. repeat x=x-1 if x == 0 break end end
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* for<br> e.g. for i=1 to 5 x=x+1 end
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* do<br> e.g. do 5 x=x+1 end
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* print<br> e.g. a=1 print
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Print is strange, it prints the last value calculated in hex and that
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is all. Please don't look at the implementation. ;-)
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is all.
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Supported operations are the following, in increasing order of
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precedence:
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@ -114,140 +104,39 @@ precedence:
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Parentheses are used to force a specific order of evaluation.
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As far as booleans go 0 is false and everything else is true. Right
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As far as booleans go, 0 is false and everything else is true. Right
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now there are only integers so this makes sense.
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Internals
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=========
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I wasn't satisfied using an external assembler and outputing assembly
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text so I wrote an x86 assembler in Ruby. It assembles just the
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instructions I need for this compiler, so it is by no means complete.
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32-bit only and no prefixes are supported. It's basically just a
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handful of instructions and mod-rm encoding. I use the system's
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linker and have no intention of writing my own, don't worry!
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It wasn't much fun generating assembly text, so I wrote an x86
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assembler library in Ruby. It implements just the instructions needed
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for this compiler and is by no means complete. It only does 32-bit
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and no prefixes are supported. It's basically just a handful of
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instructions and mod-rm encoding. I use the system's linker and have
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no intention of writing my own, don't worry!
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The code currently consists of a recursive descent parser that outputs
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x86 code in ELF binaries on Linux and Mach-O binaries on Darwin.
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Most of the code for outputing executables is Ruby, but ELF support is
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still in C and not published in the repository. Classes to output
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Mach-O and ELF binaries are found in asm/(elf|macho)writer.rb, but ELF
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support is not implemented yet so binaries only compile and run on OS
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X right now. ELF should come soon as I now have lights in my den. :)
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ELF support is still in C and not published in the repository. The
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class to output Mach-O binaries is found in asm/machofile.rb.
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Some major refactoring is needed as the project grew organically and
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in order to keep up with the tutorials I have not yet made radical
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changes. The asm/ directory holds the assembler but also the MachO
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and ELF code, for now. The assembler is a from-scratch implementation
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in Ruby. This is my first assembler and first time working with the
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x86 ISA, so it probably isn't great. It outputs horribly inefficient
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code and there are no optimizations.
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The asm/ directory holds the assembler but also the Mach-O code, for
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now. This is my first assembler and first time working with the x86
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ISA, so it probably isn't great. It outputs horribly inefficient code
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and there are no optimizations.
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Hopefully I can reduce the number of lines by factoring more, but it's
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pretty slim at ~3000 LOC. About 2100 of those are actual code. I did
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not write this compiler with the intention of anyone else reading it
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but there are a reasonable amount of comments.
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<table>
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<tr>
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<th>Real Lines</th>
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<th>Total Lines</th>
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<th>Filename</th>
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</tr>
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<tr>
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<td>87</td>
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<td>112</td>
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<td>build.rb</td>
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</tr>
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<tr>
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<td>617</td>
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<td>891</td>
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<td>compiler.rb</td>
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</tr>
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<tr>
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<td>12</td>
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<td>29</td>
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<td>asm/asm.rb</td>
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</tr>
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<tr>
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<td>569</td>
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<td>843</td>
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<td>asm/binary.rb</td>
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</tr>
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<tr>
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<td>197</td>
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<td>319</td>
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<td>asm/cstruct.rb</td>
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</tr>
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<tr>
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<td>4</td>
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<td>6</td>
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<td>asm/elfsymtab.rb</td>
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</tr>
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<tr>
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<td>4</td>
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<td>8</td>
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<td>asm/elfwriter.rb</td>
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</tr>
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<tr>
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<td>170</td>
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<td>374</td>
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<td>asm/machofile.rb</td>
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</tr>
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<tr>
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<td>95</td>
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<td>163</td>
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<td>asm/macho.rb</td>
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</tr>
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<tr>
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<td>19</td>
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<td>28</td>
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<td>asm/machosym.rb</td>
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</tr>
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<tr>
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<td>48</td>
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<td>77</td>
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<td>asm/machosymtab.rb</td>
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</tr>
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<tr>
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<td>19</td>
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<td>25</td>
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<td>asm/machowriter.rb</td>
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</tr>
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<tr>
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<td>16</td>
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<td>25</td>
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<td>asm/objwriter.rb</td>
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</tr>
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<tr>
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<td>20</td>
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<td>31</td>
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<td>asm/registers.rb</td>
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</tr>
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<tr>
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<td>42</td>
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<td>66</td>
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<td>asm/regproxy.rb</td>
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</tr>
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<tr>
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<td>56</td>
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<td>89</td>
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<td>asm/symtab.rb</td>
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</tr>
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<tr>
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<td>131</td>
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<td>183</td>
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<td>asm/text.rb</td>
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</tr>
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<tr>
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<td>2097</td>
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<td>3269</td>
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<td><b>total</b></td>
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</tr>
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</table>
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I did not write this compiler with the intention of anyone else
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reading it but there are a reasonable amount of comments.
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Happy hacking!
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What next?
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==========
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Whatever interests me really, I don't know yet.. Right now I need to
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clean up some of the code, now that object files of any size can be
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generated and tests pass again.
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Happy hacking!<br>
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-sjs
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