On Fri, Jul 1, 2011 at 6:03 PM, tiejun.chen <tiejun.c...@windriver.com> wrote: >> root@unknown:/root> insmod kprobe_example.ko func=show_interrupts >> Planted kprobe at c009be18 >> root@unknown:/root> cat /proc/interrupts >> pre_handler: p->addr = 0xc009be18, nip = 0xc009be18, msr = 0x29000 >> post_handler: p->addr = 0xc009be18, msr = 0x29000,boostable = 1 >> Oops: Exception in kernel mode, sig: 11 [#1] >> PREEMPT MPC8536 DS >> Modules linked in: kprobe_example >> NIP: df159e74 LR: c0106f40 CTR: c009be18 >> REGS: df159d90 TRAP: 0700 Not tainted (3.0.0-rc4-00001-ge8ffcca-dirty) >> MSR: 00029000 <EE,ME,CE> CR: 20202688 XER: 00000000 >> TASK = dfaa5340[613] 'cat' THREAD: df158000 >> GPR00: fffff000 df159e40 dfaa5340 df024a00 df159e78 00000000 df159f20 >> 00000001 >> GPR08: c10060d0 c009be18 00029000 df159e70 00000000 1001ca74 1ffb5f00 >> 100a01cc >> GPR16: 00000000 00000000 00000000 00000000 df024a28 df159f20 00000000 >> dfbff080 >> GPR24: 10016000 00001000 df159f20 df159e78 dfbff080 df159e78 df024a00 >> df159e70 >> NIP [df159e74] 0xdf159e74 >> LR [c0106f40] seq_read+0x2a4/0x568 >> Call Trace: >> [df159e40] [00029000] 0x29000 (unreliable) >> [df159e74] [00000000] (null) >> Instruction dump: >> XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX >> XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX >> ---[ end trace 60026bfc1fe79aed ]--- >> Segmentation fault > > Maybe I can understand this problem. > > When we kprobe these operations such as store-and-update-word for SP(r1), > > stwu r1, -A(r1) > > The program exception is triggered then PPC always allocate an exception frame > as shown as the follows: > > old r1 -------- > ... > nip > gpr[2]~gpr[31] > gpr[1] <--------- old r1 is stored here. > gpr[0] > -------- <-- pr_regs @offset 16 bytes > padding > STACK_FRAME_REGS_MARKER > LR > back chain > new r1 -------- > > Here emulate_step() is called to emulate 'stwu'. Actually this is equivalent > to > 1> update pr_regs->gpr[1] = mem(old r1 + (-A)) > 2> 'stw <old r1>, mem<(old r1 + (-A)) > > > You should notice the stack based on new r1 would be covered with mem<old r1 > +(-A)>. So after this, the kernel exit from post_krpobe, something would be > broken. This should depend on sizeof(-A). > > For kprobe show_interrupts, you can see pregs->nip is re-written violently so > kernel issued.
Yeah, my debug also show this, so this is the root cause. Thanks for your explanation. > > But sometimes we may only re-write some violate registers the kernel still > alive. And so this is just why the kernel works well for some kprobed point > after you change some kernel options/toolchains. > > If I'm correct its difficult to kprobe these stwu sp operation since the > sizeof(-A) is undermined for the kernel. So we have to implement in-depend > interrupt stack like PPC64. Hmmm, a dedicated exception stack will smooth the concern IMHO, Ben, Kuma? Thanks, Yong -- Only stand for myself _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
