## C Specification

#pragma OPENCL EXTENSION extension_name : behavior
#pragma OPENCL EXTENSION all : behavior

## Parameters

• extension_name - The name of the extension. The extension_name will have names of the form cl_khr_<name> for an extension approved by the OpenCL working group and will have names of the form cl_<vendor_name>_<name> for vendor extensions. The token all means that the behavior applies to all extensions supported by the compiler. The table below shows the legal values for extension_name:

Extension name Description

Allow writes to 3D image objects

Share memory objects wth Direct3D 10

Share memory objects wth Direct3D 11

Allow arguments to blocks passed to kernel functions to be declared as a pointer to any type

Share memory objects wth Direct3D 9

Create OpenCL event objects linked to EGL fence sync objects

Create derived resources from EGLImages

Enable Half-precision floating-point

Enable dobule-precision floating-point

Create image objects from OpenGL depth or depth-stencil textures

Link CL event objects from GL sync objects

Create image objects from OpenGL multi-sampled textures

Create image objects from OpenGL buffers, textures, and renderbuffers

Access Khronos OpenCL installable client driver loader (ICD Loader)

Standard Portable Intermediate Representation (SPIR) support

Initialize local or private memory

64-bit integer base atomic operations

64-bit integer extended atomic operations

Support for mipmap images

Priority hints

Standard Portable Intermediate Representation (SPIR) support

Allow writing to sRGB images

Implementation-controlled subgroups

Terminate an OpenCL context on a device

Throttle hints

64-bit integer support

• behavior - One of the following values:

behavior Description

enable

Behave as specified by the extension extension_name. Report an error on the #pragma OPENCL EXTENSION if the extension_name is not supported, or if all is specified.

disable

Behave (including issuing errors and warnings) as if the extension extension_name is not part of the language definition. If all is specified, then behavior must revert back to that of the non-extended core version of the language being compiled to. Warn on the #pragma OPENCL EXTENSION if the extension extension_name is not supported.

## Description

The #pragma OPENCL EXTENSION directive is a simple, low-level mechanism to set the behavior for each extension. It does not define policies such as which combinations are appropriate; those must be defined elsewhere. The order of directives matter in setting the behavior for each extension. Directives that occur later override those seen earlier. The all variant sets the behavior for all extensions, overriding all previously issued extension directives, but only if the behavior is set to disable.

The initial state of the compiler is as if the directive #pragma OPENCL EXTENSION all : disable was issued, telling the compiler that all error and warning reporting must be done according to this specification, ignoring any extensions.

Every extension which affects the OpenCL language semantics, syntax or adds built-in functions to the language must create a preprocessor #define that matches the extension name string. This #define would be available in the language if and only if the extension is supported on a given implementation.

## Notes

This document describes the list of optional features supported by OpenCL 2.1. Optional extensions may be supported by some OpenCL devices. Optional extensions are not required to be supported by a conformant OpenCL implementation, but are expected to be widely available; they define functionality that is likely to move into the required feature set in a future revision of the OpenCL specification

OpenCL extensions approved by the OpenCL working group can be promoted to required core features in later revisions of OpenCL. When this occurs, the extension specifications are merged into the core specification. Functions and enumerants that are part of such promoted extensions will have the KHR affix removed. OpenCL implementations of such later revisions must also export the name strings of promoted extensions in the CL_PLATFORM_EXTENSIONS or CL_DEVICE_EXTENSIONS string, and support the KHR-affixed versions of functions and enumerants as a transition aid.

## Example

An extension which adds the extension string "cl_khr_3d_image_writes" should also add a preprocessor #define called cl_khr_3d_image_writes. A kernel can now use this preprocessor #define to do something like the following:

#ifdef cl_khr_3d_image_writes
// do something using the extension
#else
// do something else or #error!
#endif