From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sat, 9 Jun 2001 20:24:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sat, 9 Jun 2001 20:24:04 -0400 Received: from baghira.han.de ([212.63.63.2]:8203 "EHLO baghira.han.de") by vger.kernel.org with ESMTP id ; Sat, 9 Jun 2001 20:23:47 -0400 Message-Id: From: joerg@hydrops.han.de (Joerg Ahrens) Subject: [patch] sys_modify_ldt extension (default_ldt) To: linux-kernel@vger.kernel.org Date: Sun, 10 Jun 2001 01:47:22 +0200 (MET DST) X-Mailer: ELM [version 2.4ME+ PL60 (25)] MIME-Version: 1.0 Content-Type: multipart/mixed; boundary=ELM992130442-1191-0_ Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org --ELM992130442-1191-0_ Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Hi, I am trying to integrate binfmt_xout.c into kernel 2.4 as part of the linux-abi project (formerly known as iBCS). For old Xenix 286 binaries the lcall7 gate needs to part of the LDT. In kernels 2.0 sys_modify_ldt(0,...) used to return the default_ldt (with lcall7 gate) if there were no segments set up. This behaviour changed in kernels 2.2 . As a result of a discussion with Linus, David Bruce wrote a patch for binfmt_xout.c tweaking with gdt and current->tss.ldt to get the address of default_ldt. This patch does not work any more with kernels 2.4 as tss vanished from task_struct. I do see 4 ways to cope with this problem: a) extend sys_modify_ldt with a function to retrieve the default_ldt. I did this for testing (see attached diff for arch/i386/kernel/ldt.c ). b) do some work an Davids patch but this is kind of magic for me :-) (see attached default_ldt patch) c) loose the option to compile binfmt_xout (and the rest of linux-abi) as module and simply use the symbol default_ldt. I dint't try that. d) Forget about those old fashioned 286 binaries. This option will make some linux users feel sad, as they run these progs for their daily business. Joerg -- ------------------------------------------------------------------------------ Joerg Ahrens _/ Koenigsberger Strasse 32 _/_/ 31226 Peine _/ _/ Tel.: 05171/57308 _/ _/_/_/_/ e-mail: joerg@hydrops.han.de _/_/_/_/ _/ ------------------------------------------------------------------------------ --ELM992130442-1191-0_ Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: attachment; filename=ldt.c.diff Content-Description: ldt.c.diff Content-Transfer-Encoding: 7bit --- linux-2.4.0/arch/i386/kernel/ldt.c Fri Dec 29 23:07:20 2000 +++ linux-2.4.0.i/arch/i386/kernel/ldt.c Sat Jun 9 22:48:46 2001 @@ -44,7 +44,24 @@ out: return err; } +static int read_default_ldt(void * ptr, unsigned long bytecount) +{ + int err; + unsigned long size; + void *address; + + err = 0; + address = &default_ldt[0]; + size = sizeof(struct desc_struct); + if (size > bytecount) + size = bytecount; + + err = size; + if (copy_to_user(ptr, address, size)) + err = -EFAULT; + return err; +} static int write_ldt(void * ptr, unsigned long bytecount, int oldmode) { struct mm_struct * mm = current->mm; @@ -156,6 +173,9 @@ break; case 1: ret = write_ldt(ptr, bytecount, 1); + break; + case 2: + ret = read_default_ldt(ptr, bytecount); break; case 0x11: ret = write_ldt(ptr, bytecount, 0); --ELM992130442-1191-0_ Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: attachment; filename=default_ldt_patch Content-Description: default_ldt_patch Content-Transfer-Encoding: 7bit struct desc_struct def_ldt; unsigned long *lp, *lp2; asm volatile ( "sgdt __gdt+2" ); lp = (unsigned long *)(__gdt[1] + current->tss.ldt ); lp2 = (unsigned long *)(((*lp >> 16) & 0x0000ffff) | (*(lp+1) & 0xff000000) | ((*(lp+1) << 16) & 0x00ff0000)); def_ldt.a = *lp2; def_ldt.b = *(lp2+1); --ELM992130442-1191-0_--