From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-x22b.google.com (mail-pf0-x22b.google.com [IPv6:2607:f8b0:400e:c00::22b]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id A66351A0018 for ; Wed, 17 Feb 2016 18:16:12 +1100 (AEDT) Received: by mail-pf0-x22b.google.com with SMTP id q63so6590394pfb.0 for ; Tue, 16 Feb 2016 23:16:12 -0800 (PST) Message-ID: <1455693365.3089.8.camel@gmail.com> Subject: Re: Fix BUG_ON() reporting in real mode on powerpc From: Balbir Singh To: Paul Mackerras Cc: Michael Ellerman , linuxppc-dev@lists.ozlabs.org Date: Wed, 17 Feb 2016 18:16:05 +1100 In-Reply-To: <20160217045606.GA19276@oak.ozlabs.ibm.com> References: <1455684191.3089.3.camel@gmail.com> <20160217045606.GA19276@oak.ozlabs.ibm.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , > It might be a little better to do this: > > bugaddr = regs->nip; > if (REGION_ID(bugaddr) == 0 && !(regs->msr & MSR_IR)) > bugaddr += PAGE_OFFSET; > > It is possible to execute from addresses with the 0xc000... on top in > real mode, because the CPU ignores the top 4 address bits in real > mode. Good catch! Thank you Changelog: Don't add PAGE_OFFSET blindly, check if REGION_ID is 0 I ran into this issue while debugging an early boot problem. The system hit a BUG_ON() but report bug failed to print the line number and file name. The reason being that the system was running in real mode and report_bug() searches for addresses in the PAGE_OFFSET+ region Suggested-by: Paul Mackerras Signed-off-by: Balbir Singh ---  arch/powerpc/kernel/traps.c | 7 ++++++-  1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c index b6becc7..4de4fe7 100644 --- a/arch/powerpc/kernel/traps.c +++ b/arch/powerpc/kernel/traps.c @@ -1148,6 +1148,7 @@ void __kprobes program_check_exception(struct pt_regs *regs)   goto bail;   }   if (reason & REASON_TRAP) { + unsigned long bugaddr;   /* Debugger is first in line to stop recursive faults in    * rcu_lock, notify_die, or atomic_notifier_call_chain */   if (debugger_bpt(regs)) @@ -1158,8 +1159,12 @@ void __kprobes program_check_exception(struct pt_regs *regs)   == NOTIFY_STOP)   goto bail;   + bugaddr = regs->nip; + if ((REGION_ID(bugaddr) == 0) && !(regs->msr & MSR_IR)) + bugaddr += PAGE_OFFSET; +   if (!(regs->msr & MSR_PR) &&  /* not user-mode */ -     report_bug(regs->nip, regs) == BUG_TRAP_TYPE_WARN) { +     report_bug(bugaddr, regs) == BUG_TRAP_TYPE_WARN) {   regs->nip += 4;   goto bail;   } --  2.5.0