Compiler Basics, Part 2:
This post made the front page of HNand I've incorporated some of the discussion feedback. I've also written a follow-up post that JITs Python bytecode to x The complete code is available on github.
The goal is to generate new versions of the below assembly code at runtime and execute it. Those fifteen machine code bytes comprise an x function that multiplies its argument with the constant 0xdeadbeefed. The JIT step will create functions with different such constants. While being a contrived form of specializationit illuminates the basic mechanics of just-in-time compilation.
Our general strategy is to rely on the built-in ctypes Python module to load the C standard library. From there, we can access system functions to interface with the virtual memory manager.
We'll use mmap to fetch a page-aligned block of memory. It needs to be aligned for it to become executable. That's the reason why we can't simply use the usual C function malloc, because it may return memory that spans page boundaries.
The function mprotect will be used to mark the memory block as read-only and executable. After that, we should be able to call into our freshly compiled block of code through ctypes. The boiler-plate part Before we can do anything, we need to load the standard C library.
We'll just hard-code those in our program. You can find them by digging into system header files or writing a simple C program that print them out.
A more robust and elegant solution would be to use the cffi module instead of ctypes, because it can automatically parse header files.
However, since I wanted to stick to the default CPython distribution, we'll continue using ctypes. We need a few additional constants for mmap and friends. They're just written out below. You may have to look them up for other UNIX variants. That way, we'll get exceptions if we mix invalid types.
For error reporting, it's good to have the strerror function available. We'll use munmap to destroy the machine code block after we're done with it. It lets the operating system reclaim that memory. With C, we don't need any of the above boiler-plate code.
But down the line, Python will allow us to experiment much more easily. Now we're ready to write the mmap wrapper. We mark the memory region as readable and writable with the PROT flags, and we also mark it as private and anonymous.
The latter means the memory will not be visible from other processes and that it will not be file-backed. The Linux mmap manual page covers the details but be sure to view the man page for your system.
If the mmap call fails, we raise it as a Python error. If we wanted to, we could have made it writable as well, but some systems will refuse to execute writable memory. The fun part Now we're finally ready to create an insanely simple piece of JIT code! Recall the assembly listing at the top: It's a small function — without a local stack frame — that multiplies an input number with a constant.
After all, we do create native code at runtime and execute it. It's easy to imagine more advanced examples such as JIT-compiling Brainfuck to x machine code.
Or using AVX instructions for blazing fast, vectorized math ops. The disassembly at the top of this post was actually generated by compiling and disassembling the following C code: We could have passed -S to produce a disassembly listing, but we're actually interested in the machine code, so we'll rather use a tool like objdump: First, the movabs function just puts an immediate number in the RAX register.Compiler Building Tutorial Let’s Build a Compiler October 10, Jack W.
Crenshaw. ii. Contents 1 Introduction 1 Sprint could write to a text ﬁle only if you formatted the ﬁle to go to the selected printer. I used the most common printer I could think of, the Epson MX, but even then the ﬁles ended up with.
P.D. Terry has granted permission to include his text on compiler construction on Webster. If you are not familiar with compiler concepts like grammars, lexical analysis, parsing, and other subjects, this book is an excellent introduction to the subject.
So you want to write a C++ compiler!
Just parsing C++ is a monumental effort. Most programmers can find endless entertainment writing a compiler for . How to write a very basic compiler. Ask Question. up vote down vote favorite. You may also write your own parser from scratch, but it only worth it if syntax of your language is dead simple.
The parser should detect and report syntax errors. Write a lot of test cases, both positive and negative; reuse the code you wrote while. Scratch++ Compiler V Created by nXIII. Must be downloaded to write code.
New in V NOTE: While V is not technically a rewrite, it is VERY different from V, which is why it is not V Reddit gives you the best of the internet in one place. Get a constantly updating feed of breaking news, fun stories, pics, memes, and videos just for you.
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