From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Amit S. Kale" To: Tom Rini Subject: Re: PPC KGDB changes and some help? Date: Wed, 21 Jan 2004 22:31:45 +0530 Cc: Powerpc Linux References: <20040120172708.GN13454@stop.crashing.org> <200401211946.17969.amitkale@emsyssoft.com> <20040121153019.GR13454@stop.crashing.org> In-Reply-To: <20040121153019.GR13454@stop.crashing.org> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Message-Id: <200401212231.45601.amitkale@emsyssoft.com> Sender: owner-linuxppc-dev@lists.linuxppc.org List-Id: On Wednesday 21 Jan 2004 9:00 pm, Tom Rini wrote: > On Wed, Jan 21, 2004 at 07:46:17PM +0530, Amit S. Kale wrote: > > Hi Tom, > > > > Yes. Software breakpoints have been tested in the TimeSys ppc kernel > > source. They work quite well!! I'll be releasing that code soon. > > Any chance you can give me what they gave you? I can try and merge > and test things. Done. > > The breakpoint 0xc0000000 placed by gdb is _evil_ It may clobber data. > > The gdb at kgdb.sourceforge.net places it correctly at module_event. > > I'm not quite sure what you're getting at. The gdb binary I'm using is > a good one (It's happy w/ the current kgdb stub, working in tandem w/ a > BDI2000, etc). If the breakpoints being set aren't right, I suspect > that it's related to the other problems I'm seeing. Stock gdb places a breakpoint to detect loading of shared libraries. Since kernel doesn't have the symbols that ld-linux-* has, it places that at begining of the kernel (or elsewhere I haven't been able to figure out exactly where it places it). This breakpoint corrupts kernel data many a times. The gdb I maintain at kgdb.sourceforge.net places a breakpoint correctly at module_event and detects loading of modules. > > > Where is the other breakpoint placed? While you would have certainly done > > that, please confirm that kgdb actually inserts a breakpoint where you > > have asked it to: a simple printk at the address where the breakpoint is > > placed should be sufficient. printing from gdb will not work as gdb > > removes all breakpoints before giving control to a user. > > The thing is the kernel gets into an infinite loop of stopping, as far > as gdb can tell, at the initial breakpoint I thought you could place a breakpoint somewhere and the breakpoint was never hit. ok. Now I know where it went wrong: nip is instruction pointer, not instruction contents. The change you had done compared nip to breakpoint instruction contents. > > + if (linux_regs->nip == 0x7d821008 ) > > + /* Skip over breakpoint trap insn */ > > + linux_regs->nip += 4; Checking for kgdb_setting_breakpoint is better. Following code from my patch is correct. > > + extern atomic_t kgdb_setting_breakpoint; > > + if (atomic_read(&kgdb_setting_breakpoint)) > > + regs->nip += 4; -- Amit Kale EmSysSoft (http://www.emsyssoft.com) KGDB: Linux Kernel Source Level Debugger (http://kgdb.sourceforge.net) ** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/