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.
Please report defects in this specification to arm dot acle at arm dot com.
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- Support added for TME features.
- Support added for rounding intrinsics from Armv8.5-A [ARMARMv85].
- Support added for features introduced in Armv8.5-A [ARMARMv85] (including the MTE extension).
- Support added for MVE [MVE-spec] from the Armv8.1-M architecture.
- Support added for Armv8.4-A half-precision extensions through Neon intrinsics.
- Added feature detection macro for LSE atomic operations.
- Added floating-point versions of intrinsics to access coprocessor registers.
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|
|[ARMARMv85]||(1, 2) Arm, Armv8.5 Extension, https://community.arm.com/developer/ip-products/processors/b/processors-ip-blog/posts/arm-a-profile-architecture-2018-developments-armv85a|
|[ARMv7M]||Arm, Arm Architecture Reference Manual (7-M), Arm DDI 0403C|
|[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]||Itanium C++ ABI, https://itanium-cxx-abi.github.io/cxx-abi/|
|[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|
|[MVE-spec]||Arm, Arm v8-M Architecture Reference Manual, Arm DDI0553B.F|
|[MVE]||Arm, MVE intrinsics supplement|
|[POSIX]||IEEE / TOG, The Open Group Base Specifications, IEEE 1003.1|
This document uses the following terms and abbreviations.
|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.|
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.