From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 21646 invoked by alias); 21 Jul 2003 07:11:13 -0000 Mailing-List: contact gdb-patches-help@sources.redhat.com; run by ezmlm Precedence: bulk List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sources.redhat.com Received: (qmail 21628 invoked from network); 21 Jul 2003 07:11:10 -0000 Received: from unknown (HELO zenia.home) (12.223.225.216) by sources.redhat.com with SMTP; 21 Jul 2003 07:11:10 -0000 Received: by zenia.home (Postfix, from userid 5433) id BF36E204F5; Mon, 21 Jul 2003 02:13:55 -0500 (EST) To: Daniel Jacobowitz Cc: gdb-patches@sources.redhat.com, ezannoni@redhat.com, fedor@doc.com Subject: Re: RFA symtab: Fix for PR c++/1267 ("next" and shared libraries) References: <20030719181817.GA11670@nevyn.them.org> From: Jim Blandy Date: Mon, 21 Jul 2003 07:11:00 -0000 In-Reply-To: <20030719181817.GA11670@nevyn.them.org> Message-ID: User-Agent: Gnus/5.09 (Gnus v5.9.0) Emacs/21.3 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-SW-Source: 2003-07/txt/msg00361.txt.bz2 I think this is a great idea. How widely have you tested it? Daniel Jacobowitz 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 > > 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;