From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 20762B6F54 for ; Thu, 14 Jul 2011 23:27:55 +1000 (EST) Subject: Re: [v3 PATCH 1/1] booke/kprobe: make program exception to use one dedicated exception stack Mime-Version: 1.0 (Apple Message framework v1084) Content-Type: text/plain; charset=us-ascii From: Kumar Gala In-Reply-To: <1310383915-30543-1-git-send-email-tiejun.chen@windriver.com> Date: Thu, 14 Jul 2011 08:27:44 -0500 Message-Id: References: <1310383915-30543-1-git-send-email-tiejun.chen@windriver.com> To: Tiejun Chen Cc: linuxppc-dev@ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Jul 11, 2011, at 6:31 AM, Tiejun Chen wrote: > When kprobe these operations such as store-and-update-word for SP(r1), >=20 > stwu r1, -A(r1) >=20 > The program exception is triggered, and PPC always allocate an = exception frame > as shown as the follows: >=20 > old r1 ---------- > ... > nip > gpr[2] ~ gpr[31] > gpr[1] <--------- old r1 is stored. > gpr[0] > -------- <--------- pr_regs @offset 16 bytes > padding > STACK_FRAME_REGS_MARKER > LR > back chain > new r1 ---------- > Then emulate_step() will emulate this instruction, 'stwu'. Actually = its > equivalent to: > 1> Update pr_regs->gpr[1] =3D mem[old r1 + (-A)] > 2> stw [old r1], mem[old r1 + (-A)] >=20 > Please notice the stack based on new r1 may be covered with mem[old r1 > +(-A)] when addr[old r1 + (-A)] < addr[old r1 + sizeof(an exception = frame0]. > So the above 2# operation will overwirte something to break this = exception > frame then unexpected kernel problem will be issued. >=20 > So looks we have to implement independed interrupt stack for PPC = program > exception when CONFIG_BOOKE is enabled. Here we can use > EXC_LEVEL_EXCEPTION_PROLOG to replace original NORMAL_EXCEPTION_PROLOG > for program exception if CONFIG_BOOKE. Then its always safe for kprobe > with independed exc stack from one pre-allocated and dedicated = thread_info. > Actually this is just waht we did for critical/machine check = exceptions > on PPC. >=20 > Signed-off-by: Tiejun Chen > --- I'm still very confused why we need a unique stack frame for = kprobe/program exceptions on book-e devices. Can you explain this further. - k