From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 27235 invoked by alias); 26 Jan 2009 15:38:29 -0000 Received: (qmail 27226 invoked by uid 22791); 26 Jan 2009 15:38:28 -0000 X-SWARE-Spam-Status: No, hits=-2.1 required=5.0 tests=AWL,BAYES_00 X-Spam-Check-By: sourceware.org Received: from mailhost.u-strasbg.fr (HELO mailhost.u-strasbg.fr) (130.79.200.154) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Mon, 26 Jan 2009 15:38:23 +0000 Received: from baal.u-strasbg.fr (baal.u-strasbg.fr [IPv6:2001:660:2402::41]) by mailhost.u-strasbg.fr (8.14.2/jtpda-5.5pre1) with ESMTP id n0QFcIv5064643 ; Mon, 26 Jan 2009 16:38:18 +0100 (CET) Received: from mailserver.u-strasbg.fr (ms3.u-strasbg.fr [IPv6:2001:660:2402:d::12]) by baal.u-strasbg.fr (8.14.0/jtpda-5.5pre1) with ESMTP id n0QFcIEr054254 ; Mon, 26 Jan 2009 16:38:18 +0100 (CET) (envelope-from muller@ics.u-strasbg.fr) Received: from d620muller (www-ics.u-strasbg.fr [130.79.210.225]) (user=mullerp mech=LOGIN) by mailserver.u-strasbg.fr (8.14.3/jtpda-5.5pre1) with ESMTP id n0QFcImX012945 (version=TLSv1/SSLv3 cipher=RC4-MD5 bits=128 verify=NO) ; Mon, 26 Jan 2009 16:38:18 +0100 (CET) (envelope-from muller@ics.u-strasbg.fr) From: "Pierre Muller" To: "'Mathieu Lacage'" , References: <74fef6df0901260724p188c5507x2cfa3a4283f6fd41@mail.gmail.com> In-Reply-To: <74fef6df0901260724p188c5507x2cfa3a4283f6fd41@mail.gmail.com> Subject: RE: baffling assembly-level weirdness Date: Mon, 26 Jan 2009 15:38:00 -0000 Message-ID: <005d01c97fcc$2353f310$69fbd930$@u-strasbg.fr> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Mailing-List: contact gdb-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-owner@sourceware.org X-SW-Source: 2009-01/txt/msg00171.txt.bz2 Hi, maybe you are more used to intel disassembler this is att disassembler mov 0x805e3c0,%edx means put the content of address 0x805e3c0 into register edx putting the constant 0x805e3c0 into edx would be written as mov $0x805e3c0,%edx if I am not mistaken. If you are more used to intel assembly you can use 'set disassembly-flavor intel' In your case, this means that the generated code is faulty... Pierre Muller Pascal language support maintainer for GDB > -----Message d'origine----- > De : gdb-owner@sourceware.org [mailto:gdb-owner@sourceware.org] De la > part de Mathieu Lacage > Envoy=C3=A9 : Monday, January 26, 2009 4:25 PM > =C3=80 : gdb@sourceware.org > Objet : baffling assembly-level weirdness >=20 > hi, >=20 > The following gdb session baffles me completely: %edx is reset to zero > by the mov at address 0x0804ad62 instead of being set to the constant > 0x804ad62. Of course, this code segfaults at $pc =3D 0x804ad68 when zero > is dereferenced... >=20 > Version: GNU gdb 6.8 >=20 > (gdb) disas $pc $pc+10 > Dump of assembler code from 0x804ad62 to 0x804ad6c: > 0x0804ad62 : mov 0x805e3c0,%edx > 0x0804ad68 : mov 0x14(%edx),%eax > 0x0804ad6b : cmp 0x18(%edx),%eax > End of assembler dump. > (gdb) p $pc > $3 =3D (void (*)()) 0x804ad62 > (gdb) p $edx > $4 =3D 1 > (gdb) ni > 0x0804ad68 108 return _IO_putc_unlocked (__c, stdout); > (gdb) p $edx > $5 =3D 0 > (gdb) disas $pc $pc+10 > Dump of assembler code from 0x804ad68 to 0x804ad72: > 0x0804ad68 : mov 0x14(%edx),%eax > 0x0804ad6b : cmp 0x18(%edx),%eax > 0x0804ad6e : jae 0x804adbe > 0x0804ad70 : movb $0x20,(%eax) > End of assembler dump. > (gdb) x/20bx 0x0804ad62 > 0x804ad62 : 0x8b 0x15 0xc0 0xe3 0x05 0x08 0x8b 0x42 > 0x804ad6a : 0x14 0x3b 0x42 0x18 0x73 0x4e 0xc6 0x00 > 0x804ad72 : 0x20 0x83 0xc0 0x01 >=20 > Anyone would have even a remote idea of what could have gone wrong here > ? >=20 > Mathieu > -- > Mathieu Lacage