From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e24smtp03.br.ibm.com (e24smtp03.br.ibm.com [32.104.18.24]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "e24smtp03.br.ibm.com", Issuer "Equifax" (verified OK)) by ozlabs.org (Postfix) with ESMTPS id E8588B6F69 for ; Thu, 25 Aug 2011 10:42:06 +1000 (EST) Received: from /spool/local by br.ibm.com with XMail ESMTP for from ; Wed, 24 Aug 2011 21:42:00 -0300 Received: from d24av02.br.ibm.com (d24av02.br.ibm.com [9.8.31.93]) by mailhub1.br.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p7P0ibjI1880238 for ; Wed, 24 Aug 2011 21:44:37 -0300 Received: from d24av02.br.ibm.com (loopback [127.0.0.1]) by d24av02.br.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p7P0fivv009042 for ; Wed, 24 Aug 2011 21:41:45 -0300 Subject: Re: [PATCH 2/2] [PowerPC Book3E] Introduce new ptrace debug feature flag From: Thiago Jung Bauermann To: David Gibson In-Reply-To: <20110824040010.GC30097@yookeroo.fritz.box> References: <20110819074527.GA21817@in.ibm.com> <20110819075338.GC21817@in.ibm.com> <20110823050931.GT30097@yookeroo.fritz.box> <20110823092756.GB2962@in.ibm.com> <20110824040010.GC30097@yookeroo.fritz.box> Content-Type: text/plain; charset="UTF-8" Date: Wed, 24 Aug 2011 21:41:43 -0300 Message-ID: <1314232903.14168.4.camel@hactar> Mime-Version: 1.0 Cc: linuxppc-dev@ozlabs.org, "K.Prasad" , Edjunior Barbosa Machado List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, 2011-08-24 at 14:00 +1000, David Gibson wrote: > On Tue, Aug 23, 2011 at 02:57:56PM +0530, K.Prasad wrote: > > On Tue, Aug 23, 2011 at 03:09:31PM +1000, David Gibson wrote: > > > On Fri, Aug 19, 2011 at 01:23:38PM +0530, K.Prasad wrote: > > > > > > > > While PPC_PTRACE_SETHWDEBUG ptrace flag in PowerPC accepts > > > > PPC_BREAKPOINT_MODE_EXACT mode of breakpoint, the same is not intimated to the > > > > user-space debuggers (like GDB) who may want to use it. Hence we introduce a > > > > new PPC_DEBUG_FEATURE_DATA_BP_EXACT flag which will be populated on the > > > > "features" member of "struct ppc_debug_info" to advertise support for the > > > > same on Book3E PowerPC processors. > > > > > > I thought the idea was that the BP_EXACT mode was the default - if the > > > new interface was supported at all, then BP_EXACT was always > > > supported. So, why do you need a new flag? > > > > > > > Yes, BP_EXACT was always supported but not advertised through > > PPC_PTRACE_GETHWDBGINFO. We're now doing that. > > I can see that. But you haven't answered why. BookS doesn't support BP_EXACT, that's why I suggested this flag. A BP_EXACT watchpoint triggers only when there's a memory access exactly at the given address. It doesn't trigger when there's (for example) a 4-byte write at an address immediately before which also changes the memory contents of the byte watched by the BP_EXACT watchpoint. a ranged watchpoint would trigger, so the semantics are different. As a general rule, GDB only sets ranged watchpoints and only uses BP_EXACT ones when the user sets a flag. I want GDB to fail when the user sets the flag on BookS since it can't provide the feature. -- []'s Thiago Jung Bauermann IBM Linux Technology Center