Re: [Tinycc-devel] Thumb2 codegen ready for review

[Christian Jullien]

Hi, this is really cool to have a new backend for tcc. Congrat!!

 

I had a quick look on you repository but I’m not qualified to comment it.

FYI the few last weeks I made a POC with a friend of mine to add z80 backend which generates .asm files. It is far from working but I’ve made similar changes.

 

I have more general questions:

-          How this work will be supported, I mean who (you?) will actively maintain this port so that this backend is fully synchronized and working when mob changes.

-          How can we test it? (from RPi would be nice, using a VM with emulator).

-          Do you plan to support tcc linking instead of ld? It would be a nice addition if you can.

 

My concern is that I don’t want to see a new backend that nobody will use or maintain in the next months/years.

 

C.

 

From: Tinycc-devel [mailto:tinycc-devel-bounces+eligis=address@hidden] On Behalf Of Erlend Sveen
Sent: Saturday, May 23, 2020 11:57
To: address@hidden
Subject: [Tinycc-devel] Thumb2 codegen ready for review

 

Hi,

It's been a while now since I've been working on and off various projects

for the last few months, but I finally think my TCC additions are ready for

a second pair of eyes (and more). I hope you have some time to look at it

before I try getting it into the "real" repo.

 

Initially I wrote that I would not implement any floating point stuff, but after

looking over the instruction set I found that it was way easier than I expected.

I also got TCC to run on the microcontroller itself, which also took a fair bit

of time. I think this is quite cool, lots of stories about people running

Linux on their micros but not as many about compilers as far as I can tell! In

fact I've found no articles at all after some minutes of searching. People have

done interpreters but I could not find anything for C.

 

Since I don't want to break the main repo I've put up a temporary one before I

try committing anything to the mob branch. I hoped to make it in one commit but

ended up with multiple, so here is an explanation of them and links:

 

https://git.erlendjs.no/erlendjs/tinycc/commit/9e5ef0bbab28379b1ecbd7c167892e3af5f14a8d

 

 - This adds the most of the code, please see the commit message for an

   explanation. The most important bits are of course changes to existing

   files.

 

https://git.erlendjs.no/erlendjs/tinycc/commit/8698aa391929c5c5f1ae529bda4f98f1d382545f

 

 - Once I started compiling "real" code I found some bugs, this fixes some.

 

https://git.erlendjs.no/erlendjs/tinycc/commit/3f8c5163b4d1fe2582d916a231c5e16bbbebf154

 

 - Adds float support back in and a new test, please see the commit message. It

   also cleans up a bunch of stuff, fixes some bugs and adds another test to

   trigger more branches.

 

At this point there are some things left that I have not figured out yet.

I hope maybe someone can help a bit with these, either by code or feedback on

how to do things:

 

 * Interwork between ARM state and Thumb state. Probably required to get it

   working on a Raspberry Pi. But not required for MCU use.

 * The linker in TCC does not seem to work, so I've used the GNU one.

 * Adding a flag similar to "-mcpu", "-march", "-vfp?" etc. to keep control of

   which FPU ISA it uses. I expect that the current code will cause some troble

   linking with elf files that specify e.g. no FPU despite not actually having

   generated any FPU instructions.

 * Using floats requires a Cortex-M7 with double precision, since there are

   no fallbacks to the library routines. Could be fixed if the previous point

   is implemented.

 * There is a branch in the store function that I could not figure out how to

   test, so it remains unimplemented. It is for vmov i think.

 * log10 gets the sign wrong and I have no idea why.

 

So far I've only tested using a Cortex-M7. M3 and M4 should work for integer

code but I have not gotten around to testing that yet.

 

There are also plenty of files that I figured does not belong in the TCC

repository. It mostly contains build scripts, test harness code, various notes

and so on. For an overview of how testing is going, check "tcc-hacking.ods"

here:

 

https://git.erlendjs.no/erlends-os/usr/compiler/tree/master/tinycc

 

Anyways, I think my code is ready now. It successfully compiles all my projects

that I have tried compiling, and they run properly although much slower.

 

Regards,

Erlend Sveen