From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 10238 invoked by alias); 22 Feb 2010 21:31:47 -0000 Received: (qmail 10224 invoked by uid 22791); 22 Feb 2010 21:31:46 -0000 X-SWARE-Spam-Status: No, hits=-2.5 required=5.0 tests=AWL,BAYES_00 X-Spam-Check-By: sourceware.org Received: from sibelius.xs4all.nl (HELO glazunov.sibelius.xs4all.nl) (83.163.83.176) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 22 Feb 2010 21:31:42 +0000 Received: from glazunov.sibelius.xs4all.nl (kettenis@localhost [127.0.0.1]) by glazunov.sibelius.xs4all.nl (8.14.3/8.14.3) with ESMTP id o1MLU6n2010571; Mon, 22 Feb 2010 22:30:06 +0100 (CET) Received: (from kettenis@localhost) by glazunov.sibelius.xs4all.nl (8.14.3/8.14.3/Submit) id o1MLU3ub013661; Mon, 22 Feb 2010 22:30:03 +0100 (CET) Date: Mon, 22 Feb 2010 21:31:00 -0000 Message-Id: <201002222130.o1MLU3ub013661@glazunov.sibelius.xs4all.nl> From: Mark Kettenis To: hjl.tools@gmail.com CC: dan@codesourcery.com, gdb-patches@sourceware.org In-reply-to: <6dc9ffc81002221306y6287491dv5aaac541ba303199@mail.gmail.com> (hjl.tools@gmail.com) Subject: Re: PATCH: Enable x86 XML target descriptions References: <20100218054312.GA9022@lucon.org> <201002221342.o1MDgSZA029705@glazunov.sibelius.xs4all.nl> <20100222144141.GA30100@caradoc.them.org> <6dc9ffc81002220734i15bd1279mb54cb0b64a37f3dc@mail.gmail.com> <20100222155243.GC30100@caradoc.them.org> <6dc9ffc81002220757v5e9b48bdnba56a260f0f3c0a8@mail.gmail.com> <20100222161040.GD30100@caradoc.them.org> <201002221656.o1MGuw5q009795@glazunov.sibelius.xs4all.nl> <20100222170303.GG9493@caradoc.them.org> <201002221950.o1MJoomn007989@glazunov.sibelius.xs4all.nl> <6dc9ffc81002221306y6287491dv5aaac541ba303199@mail.gmail.com> Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org X-SW-Source: 2010-02/txt/msg00559.txt.bz2 > Date: Mon, 22 Feb 2010 13:06:31 -0800 > From: "H.J. Lu" > > On Mon, Feb 22, 2010 at 11:50 AM, Mark Kettenis wrote: > >> Date: Mon, 22 Feb 2010 12:03:03 -0500 > >> From: Daniel Jacobowitz > >> > >> On Mon, Feb 22, 2010 at 05:56:58PM +0100, Mark Kettenis wrote: > >> > I've looked at the Linux kernel sources for the kernel on my > >> > workstation (2.6.27 in its OpenSUSE incarnation), and the only way to > >> > distinguish between a 32-bit and a 64-bit process seems to be to > >> > attempt to write one of the debug address registers with a value > >> > that's larger than 0xffffffff.  If that fails, you have a 32-bit > >> > process, otherwise it's a 64-bit process. > >> > >> Yuck :-(  But I didn't see anything else either. > > > > Indeed. > > > >> Is there an eflags bit for this?  Even if so, IIRC, we may not want to > >> use it; it's possible to run 32-bit code in a 64-bit process and some > >> overly clever programs may do so. > > > > Nope, there is no %eflags/%rflags bit for this.  Not quite sure what > > running 32-bit code in a 64-bit process actually means.  But I'd guess > > you want the 64-bit view on the registers in that case. > > > > Anyway, I think it's probably best if HJ leaves this bit out of this > > diff for now.  We can revisit the issue when AVX support is > > introduced. > > > > Please see if my latest patch is OK: > > --- > /* Get CS register. */ > errno = 0; > cs = ptrace (PTRACE_PEEKUSER, tid, > offsetof (struct user_regs_struct, cs), 0); > if (errno != 0) > perror_with_name (_("Couldn't get CS register")); > > /* Value of CS register: > 1. 64bit: 0x33. > 2. 32bit: 0x23. > */ > if (cs == 0x33) > return tdesc_amd64_linux; > else > return tdesc_i386_linux; > --- > > In kernel, there is > > regs->cs = test_thread_flag(TIF_64BIT_ILP32) ? __USER_CS : __USER32_CS; I fear that's rather fragile. I mean, the actual value of __USER_CS/__USER32_CS is just an implementation detail isn't it?