Re: static class member as interrupt handler works, but not if class is templated

Matthijs Kooijman <[email protected]> Mon, 12 Apr 2021 13:53:38 +0200

Newsgroups	gmane.comp.gcc.help,gmane.comp.hardware.avr.gcc
Message-ID	<[email protected]>

> > - figure out, where the special handling of the __vector_10 seems to
> > happen, and why it is not happening in the class template case. This
> > might help diagnose if and where to fix it within the compiler.
> 
> That is compiler internals... yes, if it is a compiler bug, it is the
> way to have a solution. But in that case, it seems to be a generic
> problem for gcc as attributes are not assigned to any templated class
> member functions. No idea if this is related to the target ( avr ) or
> generic for all platforms. But I never did any change inside the
> compiler. Any help is welcome!

My suspiciou would be that this is a generic gcc problem, where the
"asm" attribute is not honoured for template functions. It probably also
makes some sense, since a template is intended to be instantiated
multiple times, and each instantiation gets a name that is generated
based on (I believe) the template arguments passed, so I suspect that
the "generate a name for this template instantiation" code doesn't look
at the asm attribute.

Also note that *if* it would, then each instantiation would use the same
name and multiple instanations would result in duplicate symbols. If you
would bring this up as a gcc bug, I wouldn't be surprised that it would
be closed as wontfix for this reason.

Another workaround that I think hasn't been suggested yet, would be to
just define a global `__vector_10` function and from that just call your
templated static member. Combined with the `always_inline` attribute,
you can ensure that the call is inlined and there is no runtime overhead
(with LTO, this probably already happens when there's just a single call
to the member).

Maybe not as nice and self-contained as the asm attribute, but it does
allow multiple instantiations (where the global function defines which
instantiation is going to be used for the ISR).

Gr.

Matthijs

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