Re: eliminate deprecated_insert_raw_breakpoint. what's left.

Pedro Alves
2014-09-08T22:50:27Z

On 09/08/2014 10:34 PM, Joel Brobecker wrote:

> I was looking at how to replace that call, but I am not sure
> how to fix the code up, though. Perhaps we could just write
> the breakpoint instruction in by hand, rather than go through
> the breakpoint module? After all, it is already doing almost
> everything else by hand!

Indeed.

> In fact, looking at the code again now, I'm a little more tempted
> to see what happens if we remove it ;-).

Me too. And seriously. :-)

I traced it back to I think the original rs6000 port, in 1991...

commit 41abdfbd2de07837ba8088092765154eaa66351d
Author: John Gilmore <gnu@cygnus>
Date: Tue Nov 12 15:50:47 1991 +0000

* rs6000-pinsn.c, rs6000-tdep.c, rs6000-xdep.c, tm-rs6000.h,
xm-rs6000.h: New files.
* xcoffexec.c: New file for handling AIX shared libraries.

We already see this then, in rs6000-xdep.c:

+ /* execute one dummy instruction (which is a breakpoint) in inferior
+ process. So give kernel a chance to do internal house keeping.
+ Otherwise the following ptrace(2) calls will mess up user stack
+ since kernel will get confused about the bottom of the stack (%sp) */
+
+ exec_one_dummy_insn ();

This sounds like working around a (very) old kernel bug...
I can't believe anything resembling a modern system would need
such a monstrosity! :-) I vote just removing all that.

Thanks,
Pedro Alves