On Wed, Jun 29, 2011 at 02:23:28PM +0800, Yong Zhang wrote: > On Mon, Jun 27, 2011 at 6:01 PM, Ananth N Mavinakayanahalli > <ana...@in.ibm.com> wrote: > > On Sun, Jun 26, 2011 at 11:47:13PM +0900, Masami Hiramatsu wrote: > >> (2011/06/24 19:29), Steven Rostedt wrote: > >> > On Fri, 2011-06-24 at 17:21 +0800, Yong Zhang wrote: > >> >> Hi, > >> >> > >> >> When I use kprobe to do something, I found some wired thing. > >> >> > >> >> When CONFIG_FUNCTION_TRACER is disabled: > >> >> (gdb) disassemble do_fork > >> >> Dump of assembler code for function do_fork: > >> >> 0xc0037390 <+0>: mflr r0 > >> >> 0xc0037394 <+4>: stwu r1,-64(r1) > >> >> 0xc0037398 <+8>: mfcr r12 > >> >> 0xc003739c <+12>: stmw r27,44(r1) > >> >> > >> >> Then I: > >> >> modprobe kprobe_example func=do_fork offset=4 > >> >> ls > >> >> Things works well. > >> >> > >> >> But when CONFIG_FUNCTION_TRACER is enabled: > >> >> (gdb) disassemble do_fork > >> >> Dump of assembler code for function do_fork: > >> >> 0xc0040334 <+0>: mflr r0 > >> >> 0xc0040338 <+4>: stw r0,4(r1) > >> >> 0xc004033c <+8>: bl 0xc00109d4 <mcount> > >> >> 0xc0040340 <+12>: stwu r1,-80(r1) > >> >> 0xc0040344 <+16>: mflr r0 > >> >> 0xc0040348 <+20>: stw r0,84(r1) > >> >> 0xc004034c <+24>: mfcr r12 > >> >> Then I: > >> >> modprobe kprobe_example func=do_fork offset=12 > >> >> ls > >> >> 'ls' will never retrun. system freeze. > >> > > >> > I'm not sure if x86 had a similar issue. > >> > > >> > Masami, have any ideas to why this happened? > >> > >> No, I don't familiar with ppc implementation. I guess > >> that single-step resume code failed to emulate the > >> instruction, but it strongly depends on ppc arch. > >> Maybe IBM people may know what happened. > >> > >> Ananth, Jim, would you have any ideas? > > > > On powerpc, we emulate sstep whenever possible. Only recently support to > > emulate loads and stores got added. I don't have access to a powerpc box > > today... but will try to recreate the problem ASAP and see what could be > > happening in the presence of mcount. > > After taking more testing on it, it looks like the issue doesn't > depend on mcount > (AKA. CONFIG_FUNCTION_TRACER) > > As I said in the first email, with eldk-5.0 CONFIG_FUNCTION_TRACER=n > will work well. > > But when I'm using eldk-4.2[1], both will fail. But the funny thing is when I > set kprobe at several functions some works fine but some will fail. For > example, > at this time do_fork() works well, but show_interrupt() will crash.
Certain functions are off limits for probing -- look for __kprobe annotations in the kernel. Some such functions are arch specific, but show_interrupts() would definitely not be one of them. It works fine on my (64bit) test box. At this time, I think your best bet is to work with the eldk folks to narrow down the problem. Given the current set of data, I am inclined to think it could be an eldk bug, not a kernel one. Ananth _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
