Re: [avr-llvm-devel] Toolchain support needed!

[Borja F. <bor...@gm...>]

ping

2012/9/9 Borja Ferrer <bor...@gm...>

> Hi Eric, welcome back!
>
> Basically the situation is what I wrote in my previous email. We need to
> get a very basic toolchain working so we can complete the path from the .c
> to a .hex file. The backend should be able to compile any C code by now,
> except for new bugs and inline asm. If we're able to compile larger
> projects with the toolchain then we'll be able to detect more bugs and get
> a more reliable backend faster.
>
> Currently, clang+llc (llc is the program that does the LLVM IR to AVR asm
> conversion) is able to compile C code to .S text asm files. The missing
> steps have to be done by avr-gcc, this is: generating the object files,
> linking them and generating hex files.
> My current setup is (under linux): an avr-gcc+avr-libc installation as
> described in the avr-libc manual, and a llvm installation, both in separate
> folders.
>
> If you run this cmd line: clang -O3 test.c -o test.o -ccc-host-triple
> avr-generic-generic -ccc-gcc-name avr-gcc -mmcu=avr5
> clang drives llc to generate the .S file, then with the -ccc-gcc-name
> avr-gcc param it calls avr-gcc passing that new generated .S file so it can
> be converted to an object file with the help of the mmcu param indicating
> for what mcu we're compiling.
> avr-gcc has some logic inside where to drive the assembler and linker
> depending on the mmcu param it will call the linker with different options,
> for example the crt files involved. This is why for now we need avr-gcc,
> it's used as a driver for the linker and the assembler. Of course in the
> future we should be able to generate .o ELF files and an integrated
> assembler with llvm, but that will come later when we have a more mature
> backend.
>
> One important thing is that clang has to use avr-libc's include files not
> the system's defaults, now when I include stdio.h it's using the linux
> header file, not the avr specific one. So obviously this has to be fixed,
> but we need to know first where these files are going to be placed in our
> toolchain, i guess as a quick hack using the -I param could do it, but in
> avr-gcc nobody uses it, so we shouldn't add more complexity to the cmd line.
>
> If you need any other details, explanation or something I missed out let
> me know.
>
> 2012/9/7 Weddington, Eric <Eri...@at...>
>
> Hi Borja!
>>
>> Sorry to respond late to this email...
>>
>> This is really exciting!
>>
>> You said you need help in getting a basic toolchain working. Help me
>> understand in detail, what you have, and where you want to be.
>>
>> We need avr-gcc to run the assembler and linker. From avr-llvm, we have a
>> compiler that will compile C to assembler. I would think that we would need
>> to modify the avr-gcc specs to call the correct (new) executable for the
>> compilation step.
>>
>> If you can give me a few more details on your setup, then let's see where
>> we can go with it. :-)
>>
>> Eric
>>
>> > -----Original Message-----
>> > From: Borja Ferrer [mailto:bor...@gm...]
>> > Sent: Tuesday, August 28, 2012 4:24 PM
>> > To: avr...@li...
>> > Subject: [avr-llvm-devel] Toolchain support needed!
>> >
>> > Hello,
>> >
>> > With the latest changes, the backend is reaching the point where it can
>> > compile nearly any sort of code. One thing that is missing is support
>> for
>> > inline asm which is heavily used in avr-libc, but apart from that it
>> should be
>> > able to compile the rest. With a few tweaks i've been able to compile a
>> 2200
>> > line C file that stresses floating point calculations that produces
>> around 22k
>> > instructions (C file -> S file)
>> >
>> > Now I'm getting more interested on getting a very basic toolchain
>> working,
>> > Eric we'll need your help here. I've been able to build from a C file
>> to a hex
>> > file a very basic main() function. avr-gcc is needed to produce the elf
>> files
>> > and to drive the linker, so we'll have to stick with it for a while.
>> The setup
>> > I have is messy because avr-gcc is in one folder with avr-libc and
>> clang and
>> > llvm in another, so in order to get the toolchain with a decent setup
>> both
>> > things should be in the same folder. Also included files default to the
>> > system's not the avr specific ones. Maybe others have tried it before,
>> so i
>> > want to know how you did it or how hard it was, but in my case my first
>> try
>> > was yesterday.
>> >
>> > Also I'm going to change how register-pairs are represented because
>> avr-as
>> > can't understand what r29:r28 is. The llvm asm writer needs a bit of
>> tweaking
>> > because avr-as can't understand some asm directives it produces.
>> >
>> > This is the cmd line i'm using to generate an object file: clang -O3
>> test.c -o
>> > test.o -ccc-host-triple avr-generic-generic -ccc-gcc-name avr-gcc
>> -mmcu=avr5
>> > notice that avr-gcc is passed so that clang can drive it once the .S
>> file is
>> > generated.
>> >
>> > So try compiling a trivial main function to get the hex file generated,
>> you'll
>> > need avr-copy (provided by binutils) to convert the elf file to hex,
>> but that
>> > is easily handled by makefiles. Also people using windows try doing it
>> aswell
>> > since I dont have a setup for it and I'm looking forward for it.
>> >
>> > Once we get the basic toolchain working, adding support for avr-libc and
>> > linking programs with its libraries should be much easier. I look
>> forward for
>> > any help here!
>>
>>
>