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Re: RFA symtab: Fix for PR c++/1267 ("next" and shared libraries)
For the trunk, put it in, definitely.
For 6.0, could you test it on a COFF toolchain, and on some non-GNU
toolchain? It would be nice to have those three PR's closed in 6.0.
Daniel Jacobowitz <drow@mvista.com> writes:
> Only the testsuite on i386-linux. What would you recommend?
>
> On Mon, Jul 21, 2003 at 02:13:55AM -0500, Jim Blandy wrote:
> >
> > I think this is a great idea. How widely have you tested it?
> >
> > Daniel Jacobowitz <drow@mvista.com> writes:
> >
> > > This patch fixes c++/1267, a bug where stepping over a function call that
> > > went through the PLT (as happens when a -fPIC function makes a call to a
> > > globally visible symbol) would lose control of the inferior. I'll spare you
> > > the complete debugging session, as it really doesn't make much sense. But
> > > here's the root of the problem:
> > >
> > > When we called frame_pc_unwind on the sentinel frame, we got an address in
> > > the PLT. But when we called frame_func_unwind, we got "_init", in ".init",
> > > which is generally located right before the PLT. Then, we'd run the
> > > new-and-improved prologue unwinder on _init, and get some completely bogus
> > > information, since things weren't actually saved on the stack where it
> > > thought they were. This led to the unwound stack pointer being wrong for
> > > the step_resume breakpoint, so when we hit the step_resume breakpoint we
> > > kept going.
> > >
> > > I fixed this by changing lookup_minimal_symbol_pc_section to be paranoid
> > > about returning a minsym in the same section as the PC. Technically, at
> > > least on ELF targets, that doesn't _have_ to be true. I've never
> > > encountered an exception or a good reason for one, though. Does anyone see
> > > any pitfalls for this change? Symtab maintainers, is this patch OK?
> > >
> > > I believe this patch should also fix shlibs/1237, and may also fix
> > > shlibs/1280. Adam, could you check those?
> > >
> > >
> > >
> > >
> > >
> > > By the way, I'm convinced that all is not well in step_over_function. This
> > > comment,
> > >
> > > /* NOTE: cagney/2003-04-06:
> > >
> > > The intent of DEPRECATED_SAVED_PC_AFTER_CALL was to:
> > >
> > > - provide a very light weight equivalent to frame_unwind_pc()
> > > (nee FRAME_SAVED_PC) that avoids the prologue analyzer
> > >
> > > - avoid handling the case where the PC hasn't been saved in the
> > > prologue analyzer
> > >
> > > Unfortunatly, not five lines further down, is a call to
> > > get_frame_id() and that is guarenteed to trigger the prologue
> > > analyzer.
> > >
> > > is either incorrect or has gotten out of sync with the code:
> > >
> > > if (DEPRECATED_SAVED_PC_AFTER_CALL_P ())
> > > sr_sal.pc = ADDR_BITS_REMOVE (DEPRECATED_SAVED_PC_AFTER_CALL (get_current_frame ()));
> > > else
> > > sr_sal.pc = ADDR_BITS_REMOVE (frame_pc_unwind (get_current_frame ()));
> > > sr_sal.section = find_pc_overlay (sr_sal.pc);
> > >
> > > check_for_old_step_resume_breakpoint ();
> > > step_resume_breakpoint =
> > > set_momentary_breakpoint (sr_sal, get_frame_id (get_current_frame ()),
> > > bp_step_resume);
> > >
> > >
> > > Note that get_frame_id unwinds from the NEXT frame, and
> > > frame_pc_unwind/DEPRECATED_SAVED_PC_AFTER_CALL unwind from THIS frame.
> > > This throws me a loop every time I have to work in this function. Also, I
> > > have the nagging feeling we're saving the wrong frame. I have an old MIPS
> > > patch where I needed to use get_prev_frame in step_over_function. As soon
> > > as I have time to revisit that patch I'll be back to clean this up some
> > > more.
> > >
> > > --
> > > Daniel Jacobowitz
> > > MontaVista Software Debian GNU/Linux Developer
> > >
> > > 2003-07-19 Daniel Jacobowitz <drow@mvista.com>
> > >
> > > PR c++/1267
> > > * minsyms.c (lookup_minimal_symbol_by_pc_section): If SECTION is
> > > NULL, default to the section containing PC.
> > >
> > > Index: minsyms.c
> > > ===================================================================
> > > RCS file: /cvs/src/src/gdb/minsyms.c,v
> > > retrieving revision 1.31
> > > diff -u -p -r1.31 minsyms.c
> > > --- minsyms.c 15 May 2003 22:23:24 -0000 1.31
> > > +++ minsyms.c 19 Jul 2003 18:03:08 -0000
> > > @@ -403,12 +403,22 @@ lookup_minimal_symbol_by_pc_section (COR
> > > struct objfile *objfile;
> > > struct minimal_symbol *msymbol;
> > > struct minimal_symbol *best_symbol = NULL;
> > > + struct obj_section *pc_section;
> > >
> > > /* pc has to be in a known section. This ensures that anything beyond
> > > the end of the last segment doesn't appear to be part of the last
> > > function in the last segment. */
> > > - if (find_pc_section (pc) == NULL)
> > > + pc_section = find_pc_section (pc);
> > > + if (pc_section == NULL)
> > > return NULL;
> > > +
> > > + /* If no section was specified, then just make sure that the PC is in
> > > + the same section as the minimal symbol we find. */
> > > + if (section == NULL)
> > > + section = pc_section->the_bfd_section;
> > > +
> > > + /* FIXME drow/2003-07-19: Should we also check that PC is in SECTION
> > > + if we were passed a non-NULL SECTION argument? */
> > >
> > > for (objfile = object_files;
> > > objfile != NULL;
> >
>
> --
> Daniel Jacobowitz
> MontaVista Software Debian GNU/Linux Developer