Document revision date: 30 March 2001 | |
Order Number: AA--QSBGD--TE
Alpha privileged-code applications link against the system base image (SYS$BASE_IMAGE.EXE) on OpenVMS Alpha. This guide explains the changes that might impact Alpha privileged-code applications as a result of the OpenVMS Alpha 64-bit virtual addressing and kernel threads support provided in OpenVMS Alpha Version 7.0 and later.
Privileged-code applications from versions prior to OpenVMS Alpha Version 7.0 might require the source-code changes described in this guide.
Revision/Update Information: This manual supersedes the OpenVMS Alpha Guide to Upgrading Privileged-Code Applications, Version 7.1
Software Version: OpenVMS Alpha Version 7.3
Compaq Computer Corporation
Houston, Texas
© 2001 Compaq Computer Corporation
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Contents | Index |
Alpha privileged-code applications link against the system base image (SYS$BASE_IMAGE.EXE) on OpenVMS Alpha. This guide explains the changes that might impact Alpha privileged-code applications as a result of the OpenVMS Alpha 64-bit virtual addressing and kernel threads support provided in OpenVMS Alpha Version 7.0.
This guide is intended to help developers using privileged-code interfaces understand how the changes in OpenVMS Alpha Version 7.0 might affect their applications and device drivers.
Nonprivileged code applications should not require any source code changes and should run without modification on OpenVMS Alpha Versions 7.0 and 7.1.
The information in this document applies only to privileged-code applications on OpenVMS Alpha systems; applications on OpenVMS VAX systems are not affected.
Privileged-code applications and device drivers that were recompiled and relinked to run on OpenVMS Alpha Version 7.0 do not require source-code changes and do not have to be recompiled and relinked to run on OpenVMS Alpha Version 7.3. However, privileged-code applications from releases prior to OpenVMS Alpha Version 7.0 that were not recompiled and relinked for OpenVMS Alpha Version 7.0, might need to be recompiled and relinked to run on OpenVMS Alpha Version 7.3 and might require source-code changes as described in this guide. For more information about recompiling and relinking privileged-code applications and device drivers for OpenVMS Alpha Version 7.3, see OpenVMS Version 7.1 Release Notes. |
This guide is intended for system programmers who use privileged-mode interfaces in their applications.
The guide is divided into three parts:
For more information about how to use this guide, see Chapter 1.
For additional information about Compaq OpenVMS products and services, access the following World Wide Web address:
http://www.openvms.compaq.com/ |
1 This manual has been archived but is available on the OpenVMS Documentation CD-ROM. This information has also been included in the OpenVMS Programming Concepts Manual, Volume I. |
Compaq welcomes your comments on this manual. Please send comments to either of the following addresses:
Internet | openvmsdoc@compaq.com |
Compaq Computer Corporation
OSSG Documentation Group, ZKO3-4/U08 110 Spit Brook Rd. Nashua, NH 03062-2698 |
Use the following World Wide Web address to order additional documentation:
http://www.openvms.compaq.com/ |
If you need help deciding which documentation best meets your needs, call 800-282-6672.
The following conventions are used in this manual:
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OpenVMS Alpha Version 7.0 includes significant changes to OpenVMS Alpha privileged interfaces and data structures, mostly as a result of support for 64-bit virtual addresses and kernel threads.
For 64-bit virtual addresses, these changes are part of the infrastructure work needed to enable processes to grow their virtual address space beyond the existing 1 GB limit of P0 space and the 1 GB limit of P1 space to include P2 space, making a total of 8TB. Likewise, S2 is the extension of system space.
Kernel threads support causes significant changes to the process structure within OpenVMS (most notably to the process control block (PCB)). Although kernel threads support does not explicitly change any application programming interfaces (APIs) within OpenVMS, it does change the use of the PCB in such a way that some existing privileged code may be impacted.
As a result of these changes, some privileged-code applications might need to make source-code changes to run on OpenVMS Alpha Version 7.0 and later.
This chapter briefly describes OpenVMS Alpha Version 7.0 64-bit virtual
address and kernel threads support and suggests how you should use this
guide to ensure that your privileged-code application runs successfully
on OpenVMS Alpha Version 7.0 and later.
1.1 Quick Description of OpenVMS Alpha 64-Bit Virtual Addressing
OpenVMS Alpha Version 7.0 provides support for 64-bit virtual addresses, which makes more of the 64-bit virtual address space defined by the Alpha architecture available to the OpenVMS Alpha operating system and to application programs. The 64-bit address features allow processes to map and access data beyond the previous limits of 32-bit virtual addresses. Both process-private and system virtual address space now extend to 8 TB.
In addition to the dramatic increase in virtual address space, OpenVMS Alpha 7.0 significantly increases the amount of physical memory that can be used by individual processes.
Many tools and languages supported by OpenVMS Alpha (including the Debugger, run-time library routines, and DEC C) are enhanced to support 64-bit virtual addressing. Input and output operations can be performed directly to and from the 64-bit addressable space by means of RMS services, the $QIO system service, and most of the device drivers supplied with OpenVMS Alpha systems.
Underlying this are new system services that allow an application to allocate and manage the 64-bit virtual address space that is available for process-private use.
For more information about OpenVMS Alpha 64-bit virtual address features, see the OpenVMS Alpha Guide to 64-Bit Addressing and VLM Features1.
1 This manual has been archived but is available on the OpenVMS Documentation CD-ROM. This information has also been included in the OpenVMS Programming Concepts Manual, Volume I. |
1.2 Quick Description of OpenVMS Alpha Kernel Threads
OpenVMS Alpha Version 7.0 provides kernel threads features, which extend process scheduling capabilities to allow threads of a process to run concurrently on multiple CPUs in a multiprocessor system. The only interface to kernel threads is through the DECthreads package. Existing threaded code that uses either the CMA API or the POSIX threads API should run without change and gain the advantages provided by the kernel threads project.
Kernel threads allows a multithreaded process to execute code flows independently on more than one CPU at a time. This allows a threaded application to make better use of multiple CPUs in an SMP system. DECthreads uses these independent execution contexts as virtual CPUs and schedules application threads on them. OpenVMS then schedules the execution contexts (kernel threads) onto physical CPUs. By providing a callback mechanism from the OpenVMS scheduler to the DECthreads thread scheduler, scheduling latencies inherent in user-mode-only thread managers is greatly reduced. OpenVMS informs DECthreads when a thread has blocked in the kernel. Using this information, DECthreads can then opt to schedule some other ready thread.
For more information about kernel threads, refer to the Bookreader
version of the OpenVMS Programming Concepts Manual and Chapter 6 in this guide.
1.3 How to Use This Guide
Read Part I to learn about the changes that might be required for privileged-code applications to run on OpenVMS Alpha Version 7.0.
Refer to Part II for information about enhancing customer-written system services and device drivers with OpenVMS Version 7.0 features.
Refer to the Appendixes for more information about some of the data structures and routines mentioned throughout this guide.
The new features provided in OpenVMS Alpha Version 7.0 have required corresponding changes in internal system interfaces and data structures. These internal changes might require changes in some privileged software.
This chapter contains recommendations for upgrading privileged-code
applications to ensure that they run on OpenVMS Alpha Version 7.0. Once
your application is running on OpenVMS Alpha Version 7.0, you can
enhance it as described in Part II.
2.1 Recommendations for Upgrading Privileged-Code Applications
To ensure that a privileged-code application runs on OpenVMS Alpha Version 7.0, do the following:
This section summarizes OpenVMS Alpha Version 7.0 changes to the kernel that may require source changes in customer-written drivers and inner-mode software. The recommendations in bold face type indicate how each change can be handled.
The remaining sections in this chapter contain more details about these changes.
All device drivers, VCI clients, and inner-mode components must be recompiled and relinked to run on OpenVMS Alpha Version 7.0. |
A few necessary source changes might not always be immediately identified by compile-time or link-time warnings. Some of these are:
This section describes OpenVMS Alpha Version 7.0 changes to the I/O
subsystem that might require source changes to device drivers.
2.2.1 Impact of IRPE Data Structure Changes
As described in Section A.9, the I/O Request Packet Extension (IRPE) structure now manages a single additional locked-down buffer instead of two. The general approach to deal with this change is to use a chain of additional IRPE structures.
Current users of the IRPE may be depending on the fact that a buffer locked for direct I/O could be fully described by the irp$l_svapte , irp$l_boff , and irp$l_bcnt values. For example, it is not uncommon for an IRPE to be used in this fashion:
This approach no longer works correctly. As described in Appendix A, the DIOBM structure that is embedded in the IRP will be needed as well. Moreover, it may not be sufficient to simply copy the DIOBM from the IRP to the IRPE. In particular, the irp$l_svapte may need to be modified if the DIOBM is moved.
The general approach to this change is to lock the buffer using the IRPE directly. This approach is shown in some detail in the following example:
irpe->irpe$b_type = DYN$C_IRPE; (1) irpe->irpe$l_driver_p0 = (int) irp; (2) status = exe_std$readlock( irp, pcb, ucb, ccb, (3) buf1, buf1_len, lock_err_rtn (4) ); if( !$VMS_STATUS_SUCCESS(status) ) return status; irpe->irpe$b_rmod = irp->irp$b_rmod; (5) status = exe_std$readlock( (IRP *)irpe, pcb, ucb, ccb, (6) buf2, buf2_len, lock_err_rtn ); if( !$VMS_STATUS_SUCCESS(status) ) return status; |
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