From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sun, 10 Jun 2001 14:53:56 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sun, 10 Jun 2001 14:53:46 -0400 Received: from SMTP-OUT003.ONEMAIN.COM ([63.208.208.73]:1854 "HELO smtp07.mail.onemain.com") by vger.kernel.org with SMTP id ; Sun, 10 Jun 2001 14:53:36 -0400 Content-Type: text/plain; charset=US-ASCII From: Scott Long To: linux-kernel@vger.kernel.org Subject: Threads and the LDT (Intel-specific)? Date: Sun, 10 Jun 2001 11:53:29 -0700 X-Mailer: KMail [version 1.2] MIME-Version: 1.0 Message-Id: <01061011532900.01126@abacus> Content-Transfer-Encoding: 7BIT Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org I'm trying to do something a bit unorthodox: I want to share the address space between threads, but I want a certain region of the address space to be writeable only for a particular thread -- for all other threads this region is read-only. I've considered several approaches. I'll only go over the one I think is the best solution. I would appreciate any comments folks might have: When linking the userspace program, I instruct the linker to avoid the region from VMA 0 to VMA 0x400000. Then, in the userspace code, I duplicate the GDT entries for CS, DS, ES, SS into the LDT, except that the new segments begin at 0x400000, instead of 0. I load the segment registers with these LDT entries. In the "write-allowed" thread I create an LDT entry to address VMA 0 through VMA 0x400000, in read-write mode. In all the other threads I create an LDT entry to address the same area in read-only mode. This gives me a 4M region at the bottom of memory that is accessible in different ways to different threads. I can also use the LDT to point to thread-specific segments. IMHO this is much better than the stack trick used by linuxthreads. The problem is, I don't fully understand how to use modify_ldt(). Is anyone knowledgeable about this? If anyone has any other suggestions, please let me know. If you are confused as to why I would ever want to do this in the first place, I'd be willing to go over it off the list. Thanks, Scott