Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262240AbVCIAPX (ORCPT ); Tue, 8 Mar 2005 19:15:23 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262222AbVCIAOV (ORCPT ); Tue, 8 Mar 2005 19:14:21 -0500 Received: from nevyn.them.org ([66.93.172.17]:65433 "EHLO nevyn.them.org") by vger.kernel.org with ESMTP id S262240AbVCIANF (ORCPT ); Tue, 8 Mar 2005 19:13:05 -0500 Date: Tue, 8 Mar 2005 19:12:55 -0500 From: Daniel Jacobowitz To: Roland McGrath Cc: Linus Torvalds , Kernel Mailing List , Andrew Cagney Subject: Re: More trouble with i386 EFLAGS and ptrace Message-ID: <20050309001254.GA1496@nevyn.them.org> Mail-Followup-To: Roland McGrath , Linus Torvalds , Kernel Mailing List , Andrew Cagney References: <20050307044920.GA25093@nevyn.them.org> <200503072129.j27LTCnl030702@magilla.sf.frob.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200503072129.j27LTCnl030702@magilla.sf.frob.com> User-Agent: Mutt/1.5.6+20040907i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1938 Lines: 43 On Mon, Mar 07, 2005 at 01:29:12PM -0800, Roland McGrath wrote: > > Is this semantically different from the patch I posted, i.e. is there > > any case which one of them covers and not the other? > > Yes, the second case that I described when I said there were two cases! > (Sheesh.) Calm down, there were already two cases. I reread your message and couldn't pick out the answer, or I wouldn't have asked. > To repeat, when the process was doing PTRACE_SINGLESTEP and then > stops on some other signal rather than because of the single-step trap > (e.g. single-stepping an instruction that faults), ptrace will show TF set > in its registers. With my patch, it will show TF clear. I can reproduce this problem with the patch that Linus committed, so you should probably update your patch for a current snapshot and nag him about it. > > That is an inability to set breakpoints in the vsyscall page. Andrew > > told me (last May, wow) that he thought this worked in Fedora, but I > > haven't seen any signs of the code. It would certainly be a Good Thing > > if it is possible! > > Fedora kernels use a normal mapping (with randomized location) for the > page, rather than the fixed high address in the vanilla kernel. The > FIXADDR_USER_START area is globally mapped in a special way not using > normal vma data structures, and is permanently read-only in all tasks. > COW via ptrace works normally for Fedora's flavor, but no writing is ever > possible to the fixmap page. Blech. I assume that there is no way to map a normal VMA over top of the fixed page, for a particular process? This makes debugging the vsyscall DSO a real pain. -- Daniel Jacobowitz CodeSourcery, LLC - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/