Small C Compilers

https://bootstrapping.miraheze.org/wiki/Main_Page#Small_C_Compilers

by blacksqr • 7 years ago

227 56 7 years ago

bootstrapping.miraheze.org

codezero• 7 years ago

I love c4. The author writes very readable and simple code. I recommend trying out swieros as well “a tiny Unix like kernel”: https://github.com/rswier/swieros

snagglegaggle• 7 years ago

https://github.com/rswier/c4/blob/master/c4.c

Holy what

zik• 7 years ago

Oh wow. That's quite something.

Razengan• 7 years ago

Very readable? It's on the cusp of becoming a demon summoning ritual.

yitchelle• 7 years ago

The usage of the 2 character variable names is a "refreshing". At least the author of the code was gracious enough for the following to help debugging.

    debug;    // print executed instructions

megous2• 7 years ago

A bit terse perhaps, but only thing that is a bit more than a simple tokenization/parsing and direct output is the precedence climbing part for parsing expressions. That may cause some headscratching for some if they haven't implemented it in the past. But it's easy to read up on that algorithm on wikipedia. Anyway, even using that ultimately makes code more readable than trying to implement the same with recursive descent.

klingonopera• 7 years ago

While this is about C++, John Carmack just came from C, so a lot of this applies to C as well: https://kotaku.com/the-exceptional-beauty-of-doom-3s-source-...

userbinator3• 7 years ago

The major breakthrough of C4 is that it's both terse and yet still very readable; previously the only other well-known self-compiler of that size was OTCC, which is deliberately obfuscated.

dTal• 7 years ago

Instead of just gazing at the sea of terse variable names in awe, try actually reading it! There's only about a dozen variables and they're all documented at the top - the actual code is actually amazingly clear for what it does. There's not a lot of gratuitous cleverness.

For example, just picking a random segment, you don't have to squint very hard to see that this is a number literal parser:

  else if (tk >= '0' && tk <= '9') {
        if (ival = tk - '0') { while (*p >= '0' && *p <= '9') ival = ival * 10 + *p++ - '0'; }
        else if (*p == 'x' || *p == 'X') {
        [...goes on to handle the hexadecimal case...]

(aside - I love the conversion from string to decimal by subtracting the string value of '0', as this will work for any text encoding where the decimal digits are monotonic and contiguous - so ASCII and EBDIC at least...)

acqq• 7 years ago

It's beautiful. Here are examples of compiling c4 and using it, following the README:

    $ gcc -o c4 c4.c 2>/dev/null
    $ ./c4 hello.c
    hello, world
    exit(0) cycle = 9
    $ ./c4 -s hello.c
    1: #include <stdio.h>
    2:
    3: int main()
    4: {
    5:   printf("hello, world\n");
        ENT  0
        IMM  -274739184
        PSH
        PRTF
        ADJ  1
    6:   return 0;
        IMM  0
        LEV
    7: }
        LEV
    $ ./c4 c4.c hello.c
    hello, world
    exit(0) cycle = 9
    exit(0) cycle = 26015
    $ ./c4 c4.c c4.c hello.c
    hello, world
    exit(0) cycle = 9
    exit(0) cycle = 26015
    exit(0) cycle = 10060183

It works on Windows too, if you have gcc installed.

Also, see "Adding support for 64 bit targets" commit:

https://github.com/rswier/c4/commit/2feb8c0a142b2e513be69442...

And yes, swieros has much more.

candiodari• 7 years ago

So it's not actually a compiler, it's a bytecode compiler + interpreter (like python) where the names of the bytecodes match what an x86 assembler would use, but the encoding doesn't (and it doesn't know how to create or link .exe ELF or whatever macos uses)

tom_mellior3• 7 years ago

c4 is very cool, but it's not a compiler in the usual sense of the term. It compiles to a kind of bytecode which it then interprets (like Python, for example), but it doesn't generate assembly or machine code (like GCC or JIT compilers, for example).

But there's a more realistic compiler inside swieros: https://github.com/rswier/swieros/blob/master/root/bin/c.c that emits actual "binaries" for the emulated toy CPU. It's hard to tell what exactly is going on though, as this is not "very readable and simple code".

bicolao• 7 years ago

It's just a small step to generate machine code, this fork [1] can generate an executable, or run it JIT style, both on x86 (there's also the 'arm' branch)

[1] https://gitlab.com/pclouds/c4

unkulunkulu• 7 years ago

I must be missing something about compiler design, but why does it seem to have an interpreter at the and of main?

pygy_• 7 years ago

You went to the code too fast (a mistake I also commit often, since unlike comments/doc, code doesn’t lie...).

From the project description: “A tiny hand crafted CPU emulator, C compiler, and Operating System”

altermark• 7 years ago

c4 with tiny x86 JIT:

https://github.com/EarlGray/c4

https://github.com/EarlGray/c4/blob/master/c4x86.c

guidedlight• 7 years ago

I wonder why LCC isn’t mentioned. https://en.wikipedia.org/wiki/LCC_(compiler)

MrXOR• 7 years ago

and https://bellard.org/tcc

mhd• 7 years ago

Weirdly enough, it's mentioned in the "Past Research" section above, but not listed amongst the compilers. Maybe not small enough?

paulriddle• 7 years ago

There is also https://git.sr.ht/~mcf/cproc inspired by several other small C compilers including 8cc, c, lacc, and scc. I did not take a deep look at it yet, but it looks interesting.

userbinator3• 7 years ago

Unfortunate that "CUCU", "C Interpreter", and "Small C for I386 (IA-32)" are already dead links, although the page history shows that it was created only a little over 2 years ago.

zserge• 7 years ago

Sorry, blog layout has changed since then. https://zserge.com/posts/cucu-part1/

kragen• 7 years ago

You might want to fix the links so the old URLs work again.

msclrhd• 7 years ago

What about the Tiny C Compiler (TCC) that Fabrice Bellard wrote? https://bellard.org/tcc/

vkazanov4• 7 years ago

it not tiny anymore :-)

ainar-g2• 7 years ago

Could I ask you what do you mean by that?

Skywalker13• 7 years ago

https://bellard.org/otcc/

agumonkey2• 7 years ago

I wonder if anybody ported tcc-linux

xelxebar2• 7 years ago

In this vein, and related to the Trusting Trust Attact section, I recently came across an x86 project that works to boostrap from nothing, reling on zero external software, even for compilation.

To that end it is organizes into "phases" where the lower levels bootstrap the higher ones, with level zero essentially coding directly in x86 opcodes.

I really want to dig into it more, but for the life of me cannot find the github page again. Any ideas?

xelxebar2• 7 years ago

Aaaaand, serendipidously, I just now stumbled upon it in an HN post a bit below this one:

https://news.ycombinator.com/item?id=21201413

That article mentions the project I was thinking of:

https://github.com/oriansj/stage0

Amazingly, it seems they are even aiming to boostrap some minimal hardware as well! Super cool.

senorsmile2• 7 years ago

for some reason, I missed your reply to your own comment completely!

senorsmile2• 7 years ago

This sounds very interesting. If you find it, will you please post a link to the project?

andrewchambers• 7 years ago

This one is fantastic: https://github.com/michaelforney/cproc

jokoon• 7 years ago

I've tried to use TCC to see if it's possible to use it as a scripting language in a C++ project, and it seems to work pretty well.

(I've heard about chaiscript, but it seems way too big)

makapuf• 7 years ago

Genuine curiosity, it seems smaller than tcc? Is it by loc, by runtime mem used, by exec size ?

Crinus• 7 years ago

These look neat but they all seem to be targeting a subset of C (e.g. no struct support) instead of the full thing (even if we include stdlib). Only exception seems to be SmallerC (which as expected is larger than the other compilers/interpreters that only support a subset).

rswier• 7 years ago

I made a branch of c4 that includes struct support. I should probably add it to the master branch so it gets more visibility: https://github.com/rswier/c4/blob/switch-and-structs/c4.c

enriquto2• 7 years ago

There's also this amazing thing: http://www.simple-cc.org/

vector_spaces• 7 years ago

Anyone know what they're using for the repo web UI? http://git.simple-cc.org/scc/

enriquto2• 7 years ago

no idea, but this is a lovely, clean interface. I particularly like that file sizes are in lines

naters• 7 years ago

Pretty sure it's this: https://git.codemadness.org/stagit/

pepijndevos2• 7 years ago

Say I wrote my own CPU (which I did), which of those tiny C compilers would be easiest to retarget?

My CPU is very small, (~300 LUT4 on an FPGA using Yosys), but has a very minimal ISA. It's mostly an accumulator machine with a stack pointer.

Rietty• 7 years ago

I'm interested in what you mean by "wrote my own CPU". Could you elaborate please?

pepijndevos2• 7 years ago

https://github.com/pepijndevos/seqpu/blob/master/cpu.vhd

nils-m-holm• 7 years ago

SubC is very easy to retarget, especially the book version. It is not a full C compiler, though.

http://t3x.org/subc/

Small C Compilers

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