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

Wilhelm Meier via llvm-dev llvm-dev at lists.llvm.org
Tue Mar 31 00:37:32 PDT 2020


Just as a comparison. In gcc we get:

_vector_21:
sei
__gcc_isr 1      ;
lds r24,v1       ;  v1.1_1, v1
sts v2,r24       ;  v2, v1.1_1
__gcc_isr 2      ;
reti

Am 31.03.20 um 09:34 schrieb Wilhelm Meier via llvm-dev:
> Hi Dylan,
> 
> looks ok now.
> 
> One thing:
> 
> the ISR is now:
> 
> __vector_21:                            ; @__vector_21
> __vector_21$local:
> sei
> push    r0
> push    r1
> in      r0, 63
> push    r0
> clr     r0
> push    r24
> lds     r24, v1
> sts     v2, r24
> pop     r24
> pop     r0
> out     63, r0
> pop     r1
> pop     r0
> reti
> 
> There are unneccessary push/pops of r1 and r0 too, since the clr is
> useless ... GCC had the same problem but they made improvements.
> 
> Thanks.
> 
> 
> Am 31.03.20 um 08:09 schrieb Wilhelm Meier via llvm-dev:
>> Hi Dylan,
>>
>> thank you. I'll be back with a test ...
>>
>> Wilhelm
>>
>> Am 31.03.20 um 08:06 schrieb Dylan McKay:
>>> 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
>>> <mailto: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 <http://bm00.ir>
>>>
>>>     Please find the IR attached in the file bm00.ir <http://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>
>>>     > <mailto: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>>
>>>     >     >> <mailto: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>
>>>     <mailto: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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