Re: [RFC] Unexpected automatic language switch - get_frame_language()

[Michael Snyder <msnyder at redhat dot com>]

Joel Brobecker wrote:
> So we determine the language by looking up the symtab associated to
> the given frame pc. Unfortunately, we were not very lucky in our case
> because the call instruction was the last instruction of the function.
> And because get_frame_pc actually gives a return address (except for
> the bottom frame), the pc return is actually pointing to a different
> function. And this is where we're not lucky for the second time, because
> the next function is in a different unit written in a different
> language!


Sounds kinda like a debugging-optimized-code problem.  Your function
is tail-return optimized -- doesn't really return.  That's outside
the expected API.

I think you have to do "special" things for non-returning functions.
I've seen the same sort of thing for eg. _exit.

[...]
> So I think the correct way of doing this is to use a decremented PC
> for any frame but the bottom one. 

I think that's fixing the wrong problem.  And it's not really portable.

[...]
> PS: I couldn't reduce the testcase more, the test is too sensitive
> to code generation and placement...

That's generally a good sign of an optimization problem.