Re: Compilation with clang

[Marian Buschsieweke]

Hi David,

that is an excellent idea. The attached patch implements that idea (slightly
different) and almost makes clang happy. It know fails with:

> /usr/avr/include/avr/wdt.h:436:5: error: invalid operand for instruction
>                                 "in __tmp_reg__,__SREG__" "\n\t"
>                                 ^
> <inline asm>:1:5: note: instantiated into assembly here
>         in __tmp_reg__,__SREG__
>            ^

So I guess for my application I know only have to teach clang the value of
__tmp_reg__ (and maybe also a few other constants) to get it compiling :-)

Kind regards,
Marian

On Fri, 15 Oct 2021 09:49:30 +0200
David Brown <david@westcontrol.com> wrote:

> On 13/10/2021 18:05, Marian Buschsieweke wrote:
> > Hi together,
> > 
> > parts of the avrlibc headers are not compatible with clang. (The use case is
> > not to compile avrlibc itself with clang, but rather an application using
> > a vanilla GCC compiled avrlibc.) However, the issues are not always trivial 
> > to
> > fix.
> > 
> > E.g. in avr/wdt.h there are several instances of code like this:
> >   
> >> static __inline__
> >> __attribute__ ((__always_inline__))
> >> void wdt_enable (const uint8_t value)
> >> {
> >>    if (_SFR_IO_REG_P (_WD_CONTROL_REG))
> >>    {
> >>            __asm__ __volatile__ (
> >>                            [...]
> >>                            : /* no outputs */
> >>                            : "I" (_SFR_IO_ADDR(_WD_CONTROL_REG)),
> >>                            [...]
> >>                            : "r0"
> >>            );
> >>    }
> >>    else {
> >>            /* variant not using _WD_CONTROL_REG as immediate */
> >>            [...]       
> >>       
> >> }  
>  [...]  
> 
> It's been a /long/ time since I have done anything with the AVR, and I
> don't have a modern avr gcc compiler (or any clang avr compiler at all)
> handy for testing.  However, I have an idea you can try:
> 
>       "I" (_SFR_IO_ADDR(_WD_CONTROL_REG) || 1)
> 
> If "_SFR_IO_ADDR(_WD_CONTROL_REG)" evaluates to false, then this
> expression would give "1", which clang might be happier with.
>

fix-compilation-with-clang.patch
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