ARM Compiler toolchain v4.1 for µVision Using the Compiler

Compiler Features
4.20 Compiler eight-byte alignment features
The compiler has the following eight-byte alignment features:
• The Procedure Call Standard for the ARM Architecture (AAPCS) requires that the stack
is eight-byte aligned at all external interfaces. The compiler and C libraries preserve the
eight-byte alignment of the stack. In addition, the default C library memory model
maintains eight-byte alignment of the heap.
• Code is compiled in a way that requires and preserves the eight byte alignment constraints
at external interfaces.
• If you have assembly language files, or legacy objects, or libraries in your project, it is
your responsibility to check that they preserve eight-byte stack alignment, and correct
them if required.
• In RVCT v2.0 and later, and in ARM Compiler 4.1 and later, double and long long data
types are eight-byte aligned for compliance with the Application Binary Interface for the
ARM Architecture (AEABI). This enables efficient use of the LDRD and STRD instructions
in ARMv5TE and later.
• The default implementations of malloc(), realloc(), and calloc() maintain an eight-byte
aligned heap.
• The default implementation of alloca() returns an eight-byte aligned block of memory.
4.20.1 See also
Concepts
Using the Linker:
• Section alignment with the linker on page 4-22.
Reference
ARM ® C and C++ Libraries and Floating-Point Support Reference:
• alloca() on page 2-5.
Other information
• Procedure Call Standard for the ARM Architecture,
http://infocenter.arm.com/help/topic/com.arm.doc.ihi0042-/index.html
• Application Binary Interface (ABI) for the ARM Architecture,
http://infocenter.arm.com/help/topic/com.arm.doc.subset.swdev.abi/index.html
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