CHKPTR

IBM License Agreement for CHKPTR IF YOU DOWNLOAD OR USE THIS PROGRAM YOU AGREE TO THESE TERMS. International Business Machines corporation grants you a license to use the Program only in the country where you acquired it. The Program is copyrighted and licensed (not sold). We do not transfer title to the Program to you. You obtain no rights other that those granted you under this license. Under this license, you may: 1. use the Program on one or more machines at a time; 2. make copies of the Program for use or backup purposes within your Enterprise; and 3. modify the Program and merge it into another program. You must reproduce the copyright notice and any other legend of ownership on each copy or partial copy, of the Program. Except as expressly provided in the DAPTOOLS LIBRARY License Agreement (TOOLIC.TXT), you may NOT: 1. distribute the program in any manner, including through electronic bulletin board systems or other means; 2. sublicense, rent, lease, or assign the Program; and 3. reverse assemble, reverse compile, or otherwise translate the object code of the Program. We do not warrant that the Program is free from claims by a third party of copyright, patent, trademark, trade secret, or any other intellectual property infringement. Under no circumstances are we liable for any of the following: 1. third-party claims against you for losses or damages; 2. loss of, or damage to, your records or data; or 3. economic consequential damages (including lost profits or savings) or incidental damages, even if we are informed of their possibility. Some jurisdictions do no allow these limitations or exclusions, so they may not apply to you. We do not warrant uninterrupted or error free operation of the Program. We have no obligation to provide service, defect correction, or any maintenance for the Program. We have no obligation to supply any Program updates or enhancements to you even in such are or later become available. IF YOU DOWNLOAD OR USE THIS PROGRAM YOU AGREE TO THESE TERMS. THIS PROGRAM IS PROVIDED "AS IS" WITHOUT ANY WARRANTIES, EXPRESS OR IMPLIED, INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Some jurisdictions do not allow the exclusion of implied warranties, so the above exclusion may not apply to you. You may terminate this license at any time. We may terminate this license if you fail to comply with any of its terms. In either event, you must destroy all your copies of the Program. You are responsible for the payment of any taxes resulting from this license. You may not sell, transfer, assign, or subcontract any of your rights or obligations under this license. Any atdttempt to do so is void. Neither of us may bring a legal action more than two years after the cause of action arose. If you acquired the Program in the United States, this license is governed by the laws of the State of New York. If you acquired the Program in Canada, this license is governed by the laws of the Province of Ontario. Otherwise, this license is governed by the laws of the country in which you acquired the Program. ----------------------------------------------------------------------------- CHKPTR 1.02 14 February 1990 Author: Jim Fowler MASM subroutine for determining the validity of a pointer that points to a data item of a specified size. This routine is callable from IBM C/2 and probably other high level languages as well. Thus far it has only been tested with large model IBM C/2. This routine has not been extensively tested, but it is relatively simple and no bugs are currently known. A sample program written in C is provided to demonstrate the use of the subroutine. The following assembly instructions were used in the CHKPTR subroutine. They are available only in protect mode. LSL - Load the upper limit of a specified segment if you have access VERR - Verifies the process's ability to read from a specified segment. VERW - Verifies the process's ability to write to a specified segment. NEWS Version 1.01 - Version 1.0 had a very short life. Version 1.01 includes a modification to work around a bug in the 80386 chip. Under certain circumstances the LSL, LAR, VERR and VERW instructions can hang the 80386 CPU if they are passed an invalid selector. CHKPTR was modified to work around this bug. Thanks to Eric Rasmussen for pointing out this potential problem. Version 1.02 - Version 1.02 fixes a bug that occurred when the address offset plus data size exceeded 64K. This should always be returned as an invalid address, but due to overflow the CHKPTR function could return a valid indication. In addition a data size of zero is now treated the same as a data size of one. Thanks to Dale Jordan for finding this bug.