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Re: eliminate deprecated_insert_raw_breakpoint. what's left.
- From: Peter Schauer <peterschauer at gmx dot net>
- To: palves at redhat dot com (Pedro Alves)
- Cc: brobecker at adacore dot com (Joel Brobecker), gdb-patches at sourceware dot org (GDB Patches)
- Date: Tue, 9 Sep 2014 02:25:25 +0200 (CEST)
- Subject: Re: eliminate deprecated_insert_raw_breakpoint. what's left.
- Authentication-results: sourceware.org; auth=none
> 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!
> > 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...
No, not a bug, but consequences of a very peculiar ptrace implementation,
at least up until and including AIX 4.3.
See my other post for a more detailed explanation.
> I can't believe anything resembling a modern system would need
> such a monstrosity! :-) I vote just removing all that.
Me too, provided that newer AIX versions have a better ptrace implementation,
making this monstrosity unnecessary.
Peter Schauer Peter.Schauer@mytum.de