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1. Preface

1.1. Arm C Language Extensions

Document number: 101028

Date of Issue: 30/04/2018

1.2. Abstract

This document specifies the Arm C Language Extensions to enable C/C++ programmers to exploit the Arm architecture with minimal restrictions on source code portability.

1.3. Keywords

ACLE, ABI, C, C++, compiler, armcc, gcc, intrinsic, macro, attribute, NEON, SIMD, atomic

1.4. How to find the latest release of this specification or report a defect in it

Please check the Arm Information Center or Arm Developer Website for a later release if your copy is more than one year old.

Please report defects in this specification to arm dot acle at arm dot com.

1.5. Confidentiality status

This document is Non-Confidential.

1.5.1. Proprietary Notice

This document is protected by copyright and other related rights and the practice or implementation of the information contained in this document may be protected by one or more patents or pending patent applications. No part of this document may be reproduced in any form by any means without the express prior written permission of Arm. No license, express or implied, by estoppel or otherwise to any intellectual property rights is granted by this document unless specifically stated.

Your access to the information in this document is conditional upon your acceptance that you will not use or permit others to use the information for the purposes of determining whether implementations infringe any third party patents.

THIS DOCUMENT IS PROVIDED AS IS. Arm PROVIDES NO REPRESENTATIONS AND NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY, SATISFACTORY QUALITY, NON-INFRINGEMENT OR FITNESS FOR A PARTICULAR PURPOSE WITH RESPECT TO THE DOCUMENT. For the avoidance of doubt, Arm makes no representation with respect to, and has undertaken no analysis to identify or understand the scope and content of, third party patents, copyrights, trade secrets, or other rights.

This document may include technical inaccuracies or typographical errors.

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Copyright © 2018. Arm Limited or its affiliates. All rights reserved.

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LES-PRE-20349

1.6. About this document

1.6.1. Change control

1.6.1.1. Change history

History
Issue Date By Change
A 11/11/11 AG First release
B 13/11/13 AG Version 1.1. Editorial changes. Corrections and completions to intrinsics as detailed in 3.3. Updated for C11/C++11.
C 09/05/14 TB Version 2.0. Updated for Armv8 AArch32 and AArch64.
D 24/03/16 TB Version 2.1. Updated for Armv8.1 AArch32 and AArch64.
E 02/06/17 Arm Version ACLE Q2 2017. Updated for Armv8.2-A and Armv8.3-A.
F 30/04/18 Arm Version ACLE Q2 2018. Updated for Armv8.4-A.

The following sections highlight changes which implementers should be aware of. For tracking purposes the internal defect references (for example [ACLE-123]) are given.

1.6.1.2. Changes between ACLE Q2 2017 and ACLE Q2 2018

Most changes in ACLE Q2 2018 are updates to support features introduced in Armv8.4-A [ARMARMv84]. Support is added for the Dot Product intrinsics.

1.6.2. References

This document refers to the following documents.

[ARMARM]Arm, Arm Architecture Reference Manual (7-A / 7-R), Arm DDI 0406C
[ARMARMv8]Arm, Armv8-A Reference Manual (Issue A.b), Arm DDI0487A.B
[ARMARMv81]Arm, Armv8.1 Extension, http://community.arm.com/groups/processors/blog/2014/12/02/the-armv8-a-architecture-and-its-ongoing-development
[ARMARMv82]Arm, Armv8.2 Extension, https://community.arm.com/groups/processors/blog/2016/01/05/armv8-a-architecture-evolution
[ARMARMv83]Arm, Armv8.3 Extension, https://community.arm.com/processors/b/blog/posts/armv8-a-architecture-2016-additions
[ARMARMv84]Arm, Armv8.4 Extension, https://community.arm.com/processors/b/blog/posts/introducing-2017s-extensions-to-the-arm-architecture
[ARMv7M]Arm, Arm Architecture Reference Manual (7-M), Arm DDI 0403C
[AAPCS]Arm, Procedure Call Standard, Arm IHI 0042D
[AAPCS64]Arm, Procedure Call Standard (AArch64), Arm IHI0055C-BETA
[BA]Arm, EABI Addenda and Errata Build Attributes, Arm IHI 0045C
[CPP11]ISO, Standard C++ (based on draft N3337), ISO/IEC 14882:2011
[C11]ISO, Standard C (based on draft N1570), ISO/IEC 9899:2011
[C99]ISO, Standard C (C99), ISO 9899:1999
[cxxabi]Code-Sourcery, Itanium C++ ABI (rev. 1.86), http://mentorembedded.github.com/cxx-abi/abi.html
[G.191]ITU-T, Software Tool Library 2005 User’s Manual, T-REC-G.191-200508-I
[GCC]GNU/FSF, GNU C Compiler Collection, http://gcc.gnu.org/onlinedocs
[IA-64]Intel, Intel Itanium Processor-Specific ABI, 245370-003
[IEEE-FP]IEEE, IEEE Floating Point, IEEE 754-2008
[CFP15]ISO/IEC, Floating point extensions for C, ISO/IEC TS 18661-3
[NEON]Arm, Arm NEON Intrinsics Reference, Arm IHI0073B
[POSIX]IEEE / TOG, The Open Group Base Specifications, IEEE 1003.1
[Warren]
  1. Warren, Hacker’s Delight, pub. Addison-Wesley 2003

1.6.3. Terms and abbreviations

This document uses the following terms and abbreviations.

Term Meaning
AAPCS Arm Procedure Call Standard, part of the ABI, defined in [AAPCS].
ABI Arm Application Binary Interface.
ACLE Arm C Language Extensions, as defined in this document.
Advanced SIMD A 64-bit/128-bit SIMD instruction set defined as part of the Arm architecture.
build attributes Object build attributes indicating configuration, as defined in [BA].
ILP32 A 32-bit address mode where long is a 32-bit type.
LLP64 A 64-bit address mode where long is a 32-bit type.
LP64 A 64-bit address mode where long is a 64-bit type.
NEON An implementation of the Arm Advanced SIMD extensions.
SIMD Any instruction set that operates simultaneously on multiple elements of a vector data type.
Thumb The Thumb instruction set extension to Arm.
VFP The original Arm non-SIMD floating-point instruction set.
word A 32-bit quantity, in memory or a register.

1.7. Scope

The Arm C Language Extensions (ACLE) specification specifies source language extensions and implementation choices that C/C++ compilers can implement in order to allow programmers to better exploit the Arm architecture.

The extensions include:

  • Predefined macros that provide information about the functionality of the target architecture
  • Intrinsic functions
  • Attributes that can be applied to functions, data and other entities

This specification does not standardize command-line options, diagnostics or other external behavior of compilers.

The intended users of this specification are:

  • Application programmers wishing to adapt or hand-optimize applications and libraries for Arm targets
  • System programmers needing low-level access to Arm targets beyond what C/C++ provides for
  • Compiler implementors, who will implement this specification
  • Implementors of IDEs, static analysis and other similar tools who wish to deal with the C/C++ source language extensions when encountered in source code

ACLE is not a hardware abstraction layer (HAL), and does not specify a library component but it may make it easier to write a HAL or other low-level library in C rather than assembler.

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