Re: [patch/rfc] Try to get dummy calls working on hpux again

[Andrew Cagney <cagney@gnu.org>]

>>> Sigh (the relevant code will need comments explaining this).  Are you 
>>> absolutely positively certain this is true (for both HP/UX 10.20 / 
>>> 11.xx)? :-)
> 
> 
> there is a comment that explains this already; is this not enough?
> +      /* We set the breakpoint address and r31 to (close to) where the current
> +         pc is; when __gcc_plt_call returns, it will restore pcsqh to the
> +    current value based on this.  The -4 is needed for frame unwinding
> +    to work properly -- we need to land in a different function than
> +    the current function.  */

Given all the questions I'm asking, I think you'll want to include more 
details.  Some sort of summary of this thread.


> I've only tested on 11.11 so far.... do you mean "can we do something
> simplier with another version of HPUX", or "will this also work with
> another version of HPUX"? The answer to the latter is probably yes. The
> original code that was deleted also did something similar, but in a much
> more ugly way in some cases.
> 
> 
>>> Also that sequence in the call path, the return path, or both?
> 
> 
> both; but it is done inside of __gcc_plt_call.
> 
> 
>>> Having the dummy-code containing a non-trivial sequence of instructions 
>>> opens up the problem of needing to be able to step through them.  Issues 
>>> similar to the grief I've been going through with signal trampolines.
> 
> 
> well....
> 
> the current sequence actually is:
> current function -> dummy frame -> __gcc_plt_call -> called function

Ah! the comments should include this diagram, I think making this clear 
(and the need to fudge __gcc_plt_call) is what's really needed.

> we need to teach gdb that __gcc_plt_call (__d_plt_call) is a stub and
> how to unwind through that. i'm thinking about whether this can be done
> with the stub unwinder itself or if we need a special unwinder, because
> it doesn't follow the same calling conventions as a regular
> function/stub. <sigh>

Yes.  Probably using the tramp-frame logic.

Andrew