Home
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.
System Architecture
The System Architecture guide accompanies the QNX OS and is intended for both application developers and end-users.
Dynamic Linking
In a typical system, a number of programs will be running. Each program relies on a number of functions, some of which will be standard C library functions, like printf(), malloc(), write(), etc.
How shared objects are used
To understand how a program makes use of shared objects, let's first see the format of an executable and then examine the steps that occur when the program starts.

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.
  - The Philosophy of the QNX OS
    The primary goal of the QNX OS is to deliver the open systems POSIX API in a robust, scalable form suitable for a wide range of systems—from tiny, resource-constrained embedded systems to high-end distributed computing environments. The OS supports several processor families, including x86 and ARM.
  - The QNX OS Microkernel
    The microkernel implements the core POSIX features used in embedded realtime systems, along with the fundamental QNX OS message-passing services.
  - Interprocess Communication (IPC)
    Interprocess Communication (IPC) plays a fundamental role in the transformation of the microkernel from an embedded realtime kernel into a full-scale POSIX operating system. As various service-providing processes are added to the microkernel, IPC is the glue that connects those components into a cohesive whole.
  - The Microkernel Instrumentation
    The microkernel (procnto-smp-instr) is equipped with a sophisticated tracing and profiling mechanism that lets you monitor your system's execution in real time. This instrumentation works on both single-CPU and SMP systems.
  - Process Manager
    The Process Manager can create and manage multiple POSIX processes, each of which may contain multiple POSIX threads.
  - Dynamic Linking
    In a typical system, a number of programs will be running. Each program relies on a number of functions, some of which will be standard C library functions, like printf(), malloc(), write(), etc.
    - How shared objects are used
      To understand how a program makes use of shared objects, let's first see the format of an executable and then examine the steps that occur when the program starts.
    - Memory layout for a typical process
    - Runtime linker
      The runtime linker is invoked when a program that was linked against a shared object is started or when a program requests that a shared object be dynamically loaded. This linker is contained within the ldqnx-64.so library, which is separate from libc.
    - Loading a shared library at runtime
    - Symbol name resolution
      When the runtime linker loads a shared library, the symbols within that library have to be resolved. The order and the scope of the symbol resolution are important. If a shared library calls a function that happens to exist by the same name in several libraries that the program has loaded, the order in which these libraries are searched for this symbol is critical. This is why the OS defines several options that can be used when loading libraries.
  - Resource Managers
    To give the QNX OS a great degree of flexibility, to minimize the runtime memory requirements of the final system, and to cope with the wide variety of devices that may be found in a custom embedded system, the OS allows user-written processes to act as resource managers that can be started and stopped dynamically.
  - Filesystems
    The QNX OS provides a rich variety of filesystems. Like most service-providing processes in the OS, these filesystems execute outside the kernel; applications use them by communicating via messages generated by the shared-library implementation of the POSIX API.
  - Character I/O
    A key requirement of any realtime operating system is high-performance character I/O.
  - Networking Architecture
    As with other service-providing processes in the QNX OS, the networking services execute outside the kernel. Developers are presented with a single unified interface, regardless of the configuration and number of networks involved.
  - TCP/IP Networking
    Our TCP/IP stack is included in the io-sock networking stack and uses the common FreeBSD API.
  - High Availability
    The term High Availability (HA) is commonly used in telecommunications and other industries to describe a system's ability to remain up and running without interruption for extended periods of time.
  - What is Real Time and Why Do I Need It?
    Real time is an often misunderstood—and misapplied—property of operating systems. This appendix provides a summary of some of the critical elements of realtime computing and discusses a few design considerations and benefits.
  - Glossary
- OS Components & Operations
- Graphics
- Programming
- 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.

How shared objects are used

QNX SDP8.0System ArchitectureDeveloperUser

To understand how a program makes use of shared objects, let's first see the format of an executable and then examine the steps that occur when the program starts.

ELF format

The QNX OS uses the ELF (Executable and Linking Format) binary format. ELF not only simplifies the task of making shared libraries, but also enhances dynamic loading of modules at runtime.

In the following diagram, we show two views of an ELF file: the linking view and the execution view. The linking view, which is used when the program or library is linked, deals with sections within an object file. Sections contain the bulk of the object file information: data, instructions, relocation information, symbols, debugging information, etc. The execution view, which is used when the program runs, deals with segments.

At link time, the program or library is built by merging together sections with similar attributes into segments. Typically, all the executable and read-only data sections are combined into a single text segment, while the data and BSSs are combined into the data segment. These segments are called load segments, because they need to be loaded in memory at process creation. Other sections such as symbol information and debugging sections are merged into other, nonload segments.

Picture showing linking view and execution view — Figure 1Object file format: linking view and execution view.

ELF without COFF

Most implementations of ELF loaders are derived from COFF (Common Object File Format) loaders; they use the linking view of the ELF objects at load time. This is inefficient because the program loader must load the executable using sections. A typical program could contain a large number of sections, each of which would have to be located in the program and loaded into memory separately.

QNX OS, however, doesn't rely at all on the COFF technique of loading sections. When developing our ELF implementation, we worked directly from the ELF specification and kept efficiency paramount. The ELF loader uses the execution view of the program. By doing so, the loader's task is greatly simplified: all it has to do is copy to memory the load segments (usually two) of the program or library. As a result, process creation and library loading operations are much faster.

Page updated: March 05, 2025