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

Dylan McKay via llvm-dev llvm-dev at lists.llvm.org
Wed Mar 11 00:13:17 PDT 2020

Here you go Wilhelm,


On Thu, Mar 5, 2020 at 4:05 AM Wilhelm Meier <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
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