Re: [RFA] struct context moved

[Andrew Cagney <ac131313 at ges dot redhat dot com>]

> > Michael,
> >
> > I don't understand the rationale behind this.
> >
> > As a general trend, frame.h / struct frame is becomming increasingly
> > opaque.  I don't see a reason for moving dwarf2cfi specific stuff into
> > frame.h.
>
> Because we have
> 	struct context *context;
> in the declaration of "struct frame_info", I thought it was logical to
> declare "struct context" in the same file. Otherwise, when debugging gdb
> itself, I'm getting "incomplete type" message when examining the content
> of struct frame_info. AFAIK it doesn't increase the size of the code, it
> just gives to debugger the appropriate information about the type of
> the structure.
Ah!

GDB is going in the direction of reducing the information visible in 
header files.  ``struct gdbarch'', ``struct cmd_list_element'' and 
``struct regcache'', for instance, are all opaque.

Consequently, and very likely, ``struct frame_info'' will eventually 
become opaque.

This approach puts very strong controls over how an object can be 
accessed.  In the past GDB has relied on convention (macros) and code 
review as a way of ensuring this this is followed.  Unfortunatly, as an 
examination of the code reveals, this has proven unreliable.

As a very up-to-date example of the problem, consider the fixes Martin 
Hunt recently committed (added cmd_func()).  GDB, for some time has been 
doing the very non-portable equivalent of:

	void f (int, float);
	(void (*)(int, float, void *)) f (1, 1.0, &foo);

(assming I've got my C right :-) This was fixed in core GDB, 
Ufortunatly, because Insight (which uses GDB) was still accessing 
``struct cmd_list_element'' internals, it was missed, and that lead to 
the unintentional introduction of a core dump.  If the ``struct 
cmd_list_element'' had always been opaque, the internals change needed 
to fix this could have been implemented more robustly - the probably of 
the changes causing insight to crash would have been significantly reduced.

Anyway, I'm some what puzzled by your problem.  I suspect a stabs vs 
dwarf2 thing :-(  When I debug, I have no problems displaying things 
like ``struct gdbarch'' which is opaque.  The only other wild guess is 
to add the opaque declaration of ``struct context;'' to the top of 
"frame.h"??

enjoy,
Andrew