From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 20622 invoked by alias); 22 Feb 2010 21:41:16 -0000 Received: (qmail 20594 invoked by uid 22791); 22 Feb 2010 21:41:14 -0000 X-SWARE-Spam-Status: No, hits=-1.8 required=5.0 tests=AWL,BAYES_00,SARE_MSGID_LONG40 X-Spam-Check-By: sourceware.org Received: from mail-ww0-f41.google.com (HELO mail-ww0-f41.google.com) (74.125.82.41) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 22 Feb 2010 21:41:10 +0000 Received: by wwb24 with SMTP id 24so471142wwb.0 for ; Mon, 22 Feb 2010 13:41:08 -0800 (PST) MIME-Version: 1.0 Received: by 10.216.186.138 with SMTP id w10mr897101wem.206.1266874868505; Mon, 22 Feb 2010 13:41:08 -0800 (PST) In-Reply-To: <201002222130.o1MLU3ub013661@glazunov.sibelius.xs4all.nl> References: <20100218054312.GA9022@lucon.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> <201002222130.o1MLU3ub013661@glazunov.sibelius.xs4all.nl> Date: Mon, 22 Feb 2010 21:41:00 -0000 Message-ID: <6dc9ffc81002221341j735bdedeo7285951f4fc39c27@mail.gmail.com> Subject: Re: PATCH: Enable x86 XML target descriptions From: "H.J. Lu" To: Mark Kettenis Cc: dan@codesourcery.com, gdb-patches@sourceware.org, Suresh Siddha , "H. Peter Anvin" Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-IsSubscribed: yes 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/msg00560.txt.bz2 On Mon, Feb 22, 2010 at 1:30 PM, Mark Kettenis wr= ote: >> 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. =A0If that fails, you have a 32-bit >> >> > process, otherwise it's a 64-bit process. >> >> >> >> Yuck :-( =A0But I didn't see anything else either. >> > >> > Indeed. >> > >> >> Is there an eflags bit for this? =A0Even 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. =A0Not quite sure what >> > running 32-bit code in a 64-bit process actually means. =A0But I'd gue= ss >> > 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. =A0We can revisit the issue when AVX support is >> > introduced. >> > >> >> Please see if my latest patch is OK: >> >> --- >> =A0/* Get CS register. =A0*/ >> =A0 errno =3D 0; >> =A0 cs =3D ptrace (PTRACE_PEEKUSER, tid, >> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0offsetof (struct user_regs_struct, cs), 0= ); >> =A0 if (errno !=3D 0) >> =A0 =A0 perror_with_name (_("Couldn't get CS register")); >> >> =A0 /* Value of CS register: >> =A0 =A0 =A01. 64bit: 0x33. >> =A0 =A0 =A02. 32bit: 0x23. >> =A0 =A0*/ >> =A0 if (cs =3D=3D 0x33) >> =A0 =A0 return tdesc_amd64_linux; >> =A0 else >> =A0 =A0 return tdesc_i386_linux; >> --- >> >> In kernel, there is >> >> =A0 =A0 =A0 regs->cs =3D test_thread_flag(TIF_64BIT_ILP32) ? __USER_CS := __USER32_CS; > > I fear that's rather fragile. =A0I mean, the actual value of > __USER_CS/__USER32_CS is just an implementation detail isn't it? > That is how strace checks 32bit process on Linux/x86-64 I have discussed it with Peter and Suresh. It is very unlikely Linux kernel will break strace. In any case, we will add a new ptrace option to Linux 2.6.35 to get TIF_64BIT_ILP32 among other things. I will update gdb to try the new ptrace option first and then fail back to CS register. Thanks. --=20 H.J.