[llvm-dev] How to add new AVR targets?

[Dylan McKay via llvm-dev]

Hey Wilhelm,

That's a bug, the "interrupt" attribute is not being recognized by the
backend.

I have fixed it in
https://github.com/llvm/llvm-project/commit/339b34266c1b54a9b5ff2f83cfb1da9cd8c9d90a

Pull the latest LLVM and it should be fixed.


On Tue, Mar 31, 2020 at 8:00 AM Wilhelm Meier <wilhelm.meier at hs-kl.de>
wrote:

> Hi Dylan,
>
> I used the following commandline:
>
> clang++ -Os -DF_OSC=20000000 -DF_CPU=20000000 --target=avr  -I.
> -I../include0 -I../../include0 -I../../../include0 -I../../include0/std
> -I../include0/std -I../../../include0/std -I../../3rdparty/boost
> -I/usr/avr/include -mmcu=atmega328p
> /home/lmeier/Projekte/wmucpp/clang/bm00/bm00.cc -S -emit-llvm --output
> bm00.ir
>
> Please find the IR attached in the file bm00.ir
>
> Thanks,
>  Wilhelm
>
>
> Am 30.03.20 um 13:44 schrieb Dylan McKay:
> > Hey Wilhelm,
> >
> > Could you post the LLVM IR generated from your C++ file?
> >
> > This can be achieved with 'clang -S -emit-llvm'
> >
> > Cheers
> >
> > On Sat, Mar 28, 2020 at 6:36 PM Wilhelm Meier <wilhelm.meier at hs-kl.de
> > <mailto:wilhelm.meier at hs-kl.de>> wrote:
> >
> >     Answering partly to myself there was a extern "C" missing.
> >
> >     But the register pushes ans reti are still missing.
> >
> >     Whats wrong?
> >
> >     Am 28.03.20 um 06:26 schrieb Wilhelm Meier via llvm-dev:
> >     > Hi Dylan,
> >     >
> >     > the following code
> >     >
> >     > volatile uint8_t v1;
> >     > volatile uint8_t v2;
> >     >
> >     > __attribute__((interrupt)) void __vector_21(void)  {
> >     >     v2 = v1;
> >     > }
> >     >
> >     > produces in C mode:
> >     >
> >     > 00000092 <__vector_21>:
> >     > 92:   80 91 61 00     lds     r24, 0x0061     ; 0x800061 <v1>
> >     > 96:   80 93 60 00     sts     0x0060, r24     ; 0x800060
> <__data_end>
> >     > 9a:   08 95           ret
> >     >
> >     > and in C++ mode:
> >     >
> >     > 00000074 <_Z11__vector_21v>:
> >     > 74:   80 91 60 00     lds     r24, 0x0060     ; 0x800060
> <__data_end>
> >     > 78:   80 93 61 00     sts     0x0061, r24     ; 0x800061 <v2>
> >     > 7c:   08 95           ret
> >     >
> >     > So, in C++ mode it is not recognized as ISR due to name mangling.
> >     >
> >     > Furthermore there are no register push/pos and no reti.
> >     >
> >     > Whats wrong?
> >     >
> >     > Thanks.
> >     >
> >     >
> >     > Am 11.03.20 um 08:13 schrieb Dylan McKay:
> >     >> Here you go Wilhelm,
> >     >>
> >     >> https://github.com/dylanmckay/clang-avr-libc-interrupt-example
> >     >>
> >     >>
> >     >>
> >     >> On Thu, Mar 5, 2020 at 4:05 AM Wilhelm Meier
> >     <wilhelm.meier at hs-kl.de <mailto:wilhelm.meier at hs-kl.de>
> >     >> <mailto:wilhelm.meier at hs-kl.de <mailto:wilhelm.meier at hs-kl.de>>>
> >     wrote:
> >     >>
> >     >>     Am 04.03.20 um 13:28 schrieb Dylan McKay:
> >     >>
> >     >>     >
> >     >>     >   * *The C/C++ function needs to be declared with either
> >     the calling
> >     >>     >     convention avr-interrupt or
> >     avr-non-blocking-interrupt.* Skipping
> >     >>     >     this step will cause regular ret instructions to be
> >     emitted for
> >     >>     >     return-from-subroutine, instead of the required reti
> >     for interrupt
> >     >>     >     handlers. ISRs also have stricter requirements on which
> >     registers
> >     >>     >     must not be clobbered after execution, which the
> >     backend will
> >     >>     handle
> >     >>     >     properly by restoring all clobbered registers in the
> >     interrupt
> >     >>     >     handler epilogue
> >     >>     >   * *The symbol names of the ISR function handlers must
> >     match those
> >     >>     >     referred to in avr-libc/avr-libgcc/crt*. This is
> >     because the ISR
> >     >>     >     table is specified in assembly inside the GCC AVR CRT.
> >     The way it
> >     >>     >     works is that the external symbol references in the CRT
> >     object
> >     >>     files
> >     >>     >     are declared with an exotic linkage type that causes
> >     the linker to
> >     >>     >     skip linking of the symbols if they are undefined
> >     references.
> >     >>     If you
> >     >>     >     chose a custom ISR table in a custom CRT or runtime
> >     library, you
> >     >>     >     would be free to choose ISR names as you pleased.
> >     >>     >
> >     >>     Thank you for your explanation. But I suspect I didn't get it
> >     right. Can
> >     >>     you please provide an example?
> >     >>
> >     >>     Thanks
> >     >>
> >     > _______________________________________________
> >     > LLVM Developers mailing list
> >     > llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
> >     > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >     >
> >
>
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