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From: David Brown <david.brown@hesbynett.no>
Newsgroups: comp.arch
Subject: Re: Computer architects leaving Intel...
Date: Mon, 16 Sep 2024 18:59:21 +0200
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On 16/09/2024 17:34, Thomas Koenig wrote:
> David Brown <david.brown@hesbynett.no> schrieb:
> 
>> The GCC community would be quite happy to support such targets, but
>> someone would need to make the port.  And the architecture of the gcc
>> compiler suite is best suited to processors with reasonably regular and
>> orthogonal ISAs with plenty of registers and at least 16-bit width -
>> getting good results for a cpu like the 6502 from gcc would be an
>> extraordinary level of effort.  It makes a lot more sense to look at
>> tools like SDCC with an architecture that fits better.
> 
> Native compilation of gcc on a 6502 would be... interesting.
> 

The 6502 would be a target, rather than a host!

Of course there were C compilers, and many other languages, running on 
the 6502 BBC Micro and BBC Master computers.  But those tools were a bit 
more compact that gcc :-)

> But I think an adaption of gcc to a 6502 could actually work if
> the zero page was treated as 128 16-bit registers.  Not going
> there, though :-)

That would be a starting point, yes.  But I would not use the whole zero 
page there - perhaps just the first 32 bytes (and therefore 16 16-bit 
registers).  Having a huge register bank would make function calls tough 
when you have to stack all the callee-saved registers in your one-page 
stack!

With 16 register pairs, you would get you close to how the AVR is 
treated in gcc - it has 32 8-bit registers which are, for many purposes, 
handled in pairs by the compiler.  (Lowering ALU operations on 16-bit 
register pairs to 8-bit operations on single registers is done mostly as 
peephole optimisations at the backend.)


Someone did manage to get Linux running on an 8-bit AVR (by having the 
AVR run an ARM emulator, and using ARM Linux).  I'm sure the same 
technique could be used to host Linux on a 6502 and run gcc on it, 
though you might not consider that "native".  And "run" might be a bit 
of a misnomer - the AVR was a lot faster than a 6502, and it took 6 
hours to boot to login.

<https://dmitry.gr/?r=05.Projects&proj=07.%20Linux%20on%208bit>