[ATOMICSABI64]: Alpha Draft of Atomics ABI (#256)

This is the Alpha draft of the C/C++ Atomics Application Binary Interface 
Standard for the Arm® 64-bit Architecture

This document describes the C/C++ Atomics Application Binary Interface
for the Arm 64-bit architecture.

This document concerns the valid mappings from C/C++ Atomic Operations
to sequences of A64 instructions. This document does not support Armv7.

For matters concerning the memory model, please consult §B2 of the Arm
Architecture Reference Manual.

We focus only on a subset of the C11 atomic operations and their mapping
to A64 instructions at the time of writing.

More atomics will be added.

Co-Authored by Wilco Dijkstra (@Wilco1).

CONTRIBUTING.md

@@ -109,6 +109,7 @@ document | owner | Github handle
 [Morello extensions to ELF for the Arm 64-bit Architecture](https://github.com/ARM-software/abi-aa/tree/master/aaelf64-morello) | Silviu Baranga | @sbaranga-arm
 [Morello Descriptor ABI for the Arm 64-bit Architecture](https://github.com/ARM-software/abi-aa/tree/master/descabi-morello) | Silviu Baranga | @sbaranga-arm
 [Memtag ABI Extension to ELF for the Arm 64-bit Architecture](https://github.com/ARM-software/abi-aa/tree/master/memtagabielf64) | Mitch Phillips | @hctim
+[C/C++ Atomics Application Binary Interface Standard for the Arm 64-bit Architecture](https://github.com/ARM-software/abi-aa/tree/master/atomicsabi64) | Luke Geeson | @lukeg101
 
 3. Merging the change
 

README.md

@@ -71,6 +71,7 @@ ELF for the Arm 64-bit Architecture                                | [aaelf64](a
 DWARF for the Arm 64-bit Architecture                              | [aadwarf64](aadwarf64/aadwarf64.rst) | [2020Q2](legacy-documents/aadwarf64/ihi0057_E/IHI0057_E_2020Q2_aadwarf64.pdf)
 C++ ABI for the Arm 64-bit Architecture                            | [cppabi64](cppabi64/cppabi64.rst)    | [2020Q2](legacy-documents/cppabi64/ihi0059_E/IHI0059E_2020Q2_cppabi64.pdf)
 Vector Function ABI for the Arm 64-bit Architecture                | [vfabia64](vfabia64/vfabia64.rst)    | [2019Q2](legacy-documents/vfabia64/101129_1920/101129_1920_01_en.pdf)
+C/C++ Atomics ABI for the Arm 64-bit Architecture                  | [atomicsabi64](atomicsabi64/atomicsabi64.rst)    | n/a
 
 
 ### ABI for the Arm 64-bit Architecture with SVE support

atomicsabi64/CONTRIBUTIONS

@@ -0,0 +1,3 @@
+Contributions to this project are licensed under an inbound=outbound
+model such that any such contributions are licensed by the contributor
+under the same terms as those in the LICENSE file.

atomicsabi64/LICENSE

@@ -0,0 +1,22 @@
+This work is licensed under the Creative Commons
+Attribution-ShareAlike 4.0 International License. To view a copy of
+this license, visit http://creativecommons.org/licenses/by-sa/4.0/ or
+send a letter to Creative Commons, PO Box 1866, Mountain View, CA
+94042, USA.
+
+Grant of Patent License. Subject to the terms and conditions of this
+license (both the Public License and this Patent License), each
+Licensor hereby grants to You a perpetual, worldwide, non-exclusive,
+no-charge, royalty-free, irrevocable (except as stated in this
+section) patent license to make, have made, use, offer to sell, sell,
+import, and otherwise transfer the Licensed Material, where such
+license applies only to those patent claims licensable by such
+Licensor that are necessarily infringed by their contribution(s) alone
+or by combination of their contribution(s) with the Licensed Material
+to which such contribution(s) was submitted. If You institute patent
+litigation against any entity (including a cross-claim or counterclaim
+in a lawsuit) alleging that the Licensed Material or a contribution
+incorporated within the Licensed Material constitutes direct or
+contributory patent infringement, then any licenses granted to You
+under this license for that Licensed Material shall terminate as of
+the date such litigation is filed.

atomicsabi64/README.md

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+<div align="center">
+   <img src="Arm_logo_blue_RGB.svg" />
+</div>
+
+# C/C++ Atomics ABI for the Arm® 64-bit Architecture (AArch64)
+
+
+## About this document
+
+This document describes the [Application Binary Interface for the use
+of code generated by compiling C/C++ atomics targeting the Arm 64-bit architecture](atomicsabi64.rst).
+
+## About the license
+
+As identified more fully in the [LICENSE](LICENSE) file, this project
+is licensed under CC-BY-SA-4.0 along with an additional patent
+license.  The language in the additional patent license is largely
+identical to that in Apache-2.0 (specifically, Section 3 of Apache-2.0
+as reflected at https://www.apache.org/licenses/LICENSE-2.0) with two
+exceptions.
+
+First, several changes were made related to the defined terms so as to
+reflect the fact that such defined terms need to align with the
+terminology in CC-BY-SA-4.0 rather than Apache-2.0 (e.g., changing
+“Work” to “Licensed Material”).
+
+Second, the defensive termination clause was changed such that the
+scope of defensive termination applies to “any licenses granted to
+You” (rather than “any patent licenses granted to You”).  This change
+is intended to help maintain a healthy ecosystem by providing
+additional protection to the community against patent litigation
+claims.
+
+## Defects report
+
+Please report defects in the [Atomics Application Binary Interface (ABI)
+for the Arm 64-bit architecture](atomicsabi64.rst) to the [issue tracker
+page on GitHub](https://github.com/ARM-software/abi-aa/issues).

atomicsabi64/TRADEMARK_NOTICE

@@ -0,0 +1,8 @@
+The text of and illustrations in this document are licensed
+under a Creative Commons Attribution–Share Alike 4.0 International
+license ("CC-BY-SA-4.0”), with an additional clause on patents.
+The Arm trademarks featured here are registered trademarks or
+trademarks of Arm Limited (or its subsidiaries) in the US and/or
+elsewhere. All rights reserved. Please visit
+https://www.arm.com/company/policies/trademarks for more information
+about Arm’s trademarks.