Hitchikers Guide to Porting Phobos / D Runtime to other architectures

[Mike]

On Monday, 6 January 2014 at 11:47:57 UTC, Dwhatever wrote:
> I'm trying to do the same, trying to compile OS free code but I 
> haven't so far been successful because D requires the runtime 
> and then also Phobos. Compared to C/C++ where you can create 
> pretty advanced stand alone code without even include any 
> standard libraries, this because much of C++ is part of the 
> compiler.

I created a bare-metal freestanding (OS Free) hello world program 
and wrote a wiki about it here 
(http://wiki.dlang.org/Extremely_minimal_semihosted_%22Hello_World%22)

The problem is that there's not really much D in that D program, 
but it is a working foundation on which to build.  If you plan on 
writing D code for embedded systems, you probably don't want all 
of the runtime anyway (at least I don't).

Using GDC compiled for arm-none-eabi, I created a malloc/free 
implementation in D and am now able to create classes that are 
allocated on the heap with "new" and deallocated using "destroy". 
  I also created a reference counted implementation too that 
automatically deallocates when the reference count reaches 0.  
But, I'm still struggling with the memory management as a whole.

Unfortunately once I started creating structs and classes I had 
to implement a bunch of "TypeInfo.." stuff in object.d even 
though it appears none of it gets used.  My object.d is now only 
about 140 lines.

This was only possible with a recent change to GDC 
(http://forum.dlang.org/post/mailman.3.1387377012.2938.d.gnu@puremagic.com) 
and the -fno-emit-moduleinfo switch.  I tried with LDC too, but 
LDC requires the world, so I gave up for now.

If any compiler implementers are reading this, please try to 
generate only code that is used by the program being compiled.  I 
need to get this sorted out and submit some bug/enhancement 
requests to the compiler writers, but I first need to understand 
things better so I can articulate it well.

> With D this is not the case. I don't really have a good picture 
> what is part of the compiler or the runtime. Even creating a 
> simple sample class and create a stack object requires that I 
> include *everything*, that hairy runtime phobos nest. The 
> runtime also has dependencies into Phobos which I find to be 
> very inconvenient and I don't think it is a good idea. The 
> runtime should be stand alone and Phobos should depended on the 
> runtime and not vice versa.

I sympathize and agree.  I can't see the abstraction in the 
phobos/runtime hairball.  That's why I'm throwing the baby out 
with the bathwater and making a new baby.

I also wish the runtime wasn't so coupled to the garbage 
collector.  The garbage collector is just one of several ways to 
manage memory, and I don't think the runtime should be so 
dependent on it, but that's probably easier said than done.

> Compared to C/C++, D is very hard to get to work in the 
> embedded/OS less environment because of this.

I agree, but it won't get any better until you and I step up and 
do something about it.