Outline

Purpose
Classes
Description

Purpose

Provide implementations of atomic operations for ARM/GCC.

Classes

bsls::AtomicOperations_ARM_ALL_GCC: implementation of atomics for ARM/GCC.

Description

This component provides classes necessary to implement atomics on the Linux ARM platform with GCC. The classes are for private use only. See bsls_atomicoperations and bsls_atomic for the public interface to atomics.

IMPLEMENTATION NOTES: Wherever possible we use atomic intrinsics that both GCC 4.6+ and Clang 3.2+ support. Otherwise the inline assembly code is used that can be compiled both by GCC and Clang. This puts some restrictions on the assembly code because Clang doesn't support register pairs that represent a 64bit value. So instead of ldrexd %1, H1, [%3] the exact registers have to be specified, as in ldrexd r2, r3, [%3]. Note also that operations like ldrexd and stdrexd are supported only starting from armv6zk, so not every armv6 platform will work.

For more details on ARM atomic primitives see the Linux kernel source code (arch/arm/include/asm/atomic.h) and the "C/C++11 mappings to processors" (http://www.cl.cam.ac.uk/~pes20/cpp/cpp0xmappings.html), and the "ARM1156T2F-S Technical Reference Manual" (http://infocenter.arm.com/help/index.jsp? topic=/com.arm.doc.ddi0290g/Babebdcb.html), which contains documentation on the p15 coprocessor opcodes used in this component).