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QNX Software Development Platform
QNX SDP is a cross-compiling and debugging environment, including an IDE and command-line tools, for building binary images and programs for target boards running the QNX OS 8.0.
Programming
Programmer's Guide
The QNX OS Programmer's Guide covers a variety of topics that might interest developers who are building applications that will run under the QNX OS.
Working with Memory
(or The Persistence of Memory, with a nod to Salvador Dali) In the Process Manager chapter of the System Architecture guide, we looked at how the OS manages memory. This chapter describes how you can work with memory.
Shared memory
Shared memory is an efficient way to share data among different processes.
Revoking access to a shared memory object
The creator of a shared memory object can revoke another process's mappings of the object.

QNX Momentics IDE User's Guide
This User's Guide describes version 8.0 of the Integrated Development Environment (IDE) that's part of the QNX Tool Suite.
QNX Software Development Platform
QNX SDP is a cross-compiling and debugging environment, including an IDE and command-line tools, for building binary images and programs for target boards running the QNX OS 8.0.
- Quickstart Guide
- System Architecture
  The System Architecture guide accompanies the QNX OS and is intended for both application developers and end-users.
- OS Components & Operations
- Graphics
- Programming
  - Getting Started with the QNX OS
    Getting Started with the QNX OS: A Guide for Realtime Programmers is intended to introduce you to the QNX OS and help you develop applications and resource managers for it.
  - Programmer's Guide
    The QNX OS Programmer's Guide covers a variety of topics that might interest developers who are building applications that will run under the QNX OS.
    - Compiling and Debugging
      Let's start by looking at some things you should consider when you start to write a program for the QNX OS.
    - QNX OS Architecture and Concepts
      The QNX OS architecture consists of the microkernel and several cooperating processes. These processes communicate with each other via various forms of interprocess communication (IPC). Message passing is the primary form of IPC in QNX OS.
    - Processes
      Your applications should be written in a way that reflects the architecture of the QNX OS—as a set of cooperating processes. In this chapter, we see how to start processes (also known as creating processes) from code, how to terminate them, and how to detect their termination.
    - Multicore Processing
      Multiprocessing systems, whether discrete or multicore, can greatly improve your applications' performance.
    - Working with Access Control Lists (ACLs)
      Some filesystems, such as the Power-Safe (fs-qnx6.so) and QNX compressed filesystems, extend file permissions with Access Control Lists, which are based on the withdrawn IEEE POSIX 1003.1e and 1003.2c draft standards.
    - Understanding the Microkernel's Concept of Time
      Whether you're working with timers or simply getting the time of day, it's important that you understand how the OS works with time.
    - Handling Hardware Interrupts
      This chapter explains the QNX OS mechanisms for quickly reacting to hardware events.
    - Working with Memory
      (or The Persistence of Memory, with a nod to Salvador Dali) In the Process Manager chapter of the System Architecture guide, we looked at how the OS manages memory. This chapter describes how you can work with memory.
      - Memory objects
        A memory object is a container for physical memory.
      - Memory management in QNX OS
        Let's consider memory management in general.
      - Memory initialization
        Memory initialization happens when physical pages are associated with virtual addresses via mmap() calls.
      - Dynamic memory management
        Let's examine how the heap is used for dynamically allocated memory.
      - Typed memory
        Your system's startup program can reserve memory pools to be used for special purposes, such as graphics. These pools are separate from SYSRAM.
      - Shared memory
        Shared memory is an efficient way to share data among different processes.
        Secure buffer management
        Shared memory is a powerful and efficient method of IPC, but there are ways to make it more secure.
        Anonymous shared objects
        Using an anonymous shared object eliminates the need for a publically visible name.
        Shared memory handles
        Shared memory handles let you share buffers among processes without using public pathnames.
        Sealing a shared memory object
        Sealing a shared memory object is a way for the creator of the object to prevent other processes from changing the object's physical layout, even if they're allowed to change the memory contents.
        Revoking access to a shared memory object
        The creator of a shared memory object can revoke another process's mappings of the object.
        Putting it all together: using handles with anonymous, revocable, and sealed shared memory objects
        To retain the most control over a shared memory object, the creator must use a handle with an anonymous, revocable, and sealed shared memory object.
        Getting information about the layout of a shared memory object
        If you need to get information about the layout of a memory object (for example, to program a DMA engine or IOMMU), you can send a _MEM_OBJ_INFO message to the memory manager.
        Sharing memory through the direct mapping of physical addresses
      - Heap analysis
        If you develop a program that dynamically allocates memory, you're also responsible for tracking any memory that you allocate whenever a task is performed, and for releasing that memory when you no longer need it. If you fail to track the memory correctly, you may introduce memory leaks or unintentionally write to an area outside of the allocated memory space.
    - Freedom from Hardware and Platform Dependencies
      The QNX OS can run on many different hardware platforms. The way in which applications can access peripheral devices and how data is stored varies between platforms. This chapter explains our solutions for minimizing the impact of such platform dependencies.
    - Conventions for Recursive Makefiles and Directories
      In this chapter, we'll look at the supplementary files used in the QNX OS development environment. Although we use the standard make command to create libraries and executables, we also use some of our own conventions in the Makefile syntax.
    - Glossary
  - Writing a Resource Manager
- System Security Guide
  The QNX System Security Guide is intended for both system integrators who are responsible for the security of a QNX OS system and developers who want to create a QNX OS resource manager free from vulnerabilities.
- Utilities & Libraries
- Migrating to QNX OS 8.0
QNX Software in the Cloud
QNX Software in the Cloud enables developers to use the QNX OS in the Amazon cloud environment.
QNX Toolkit for Visual Studio Code
This User's Guide describes the QNX^® Toolkit for Visual Studio Code. The guide introduces you to the QNX Toolkit by explaining the QNX development environment and how to build, run, and debug your QNX^® Operating System (OS) applications and systems.
QNX Hypervisor User's Guide
This User's Guide explains the QNX hypervisor architecture and provides instructions for installing and running a QNX Hypervisor system, changing system components and configuration, and using hypervisor features such as virtual devices (vdevs).
Typographical Conventions, Support, and Licensing
This section describes the typographical conventions used throughout the documentation, explains how to obtain technical support, and provides some information about licensing.

Revoking access to a shared memory object

QNX SDP8.0Programmer's GuideDeveloper

The creator of a shared memory object can revoke another process's mappings of the object.

For example:

Note:

This example focuses on resource managers but it also applies to any process that provides a reference to a shared memory object it owns to another process.

Figure 1Illustration of how the resource manager responds to a devious client's attempt to fool it.

The user interface to support this scenario includes:

a SHMCTL_REVOCABLE flag passed to shm_ctl() that marks a shared memory object as revocable.
a shm_revoke() function that you can use on a revocable object to remove mappings for either one particular process or all processes with mappings to it.

So that a process can't protect against revocation by forking, revocable object regions are marked as MAP_NOINHERIT; the memory maps for these regions won't exist in the child.

For the steps to follow in using revocable shared memory objects, see Putting it all together: using handles with anonymous, revocable shared memory objects, below.

The discussion above focuses on the case where the creator of a shared memory object doesn't trust the other process. What about the opposite case, where the other process doesn't trust the creator? The other process could check the object's flags (see the SHMCTL_GET_FLAGS bit for shm_ctl()) and decide not to use the object, or it could access the mapped memory carefully, using sigsetjmp() or a similar mechanism. There's not much the creator and the other process can do if neither trusts the other.

Page updated: March 05, 2025