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Compiler User Guide

Preface Overview of the Compiler Getting Started with the Compiler Compiler Features Compiler intrinsics Performance benefits of compiler intrinsics ARM assembler instruction intrinsics Generic intrinsics Compiler intrinsics for controlling IRQ and FIQ in Compiler intrinsics for inserting optimization bar Compiler intrinsics for inserting native instructi Compiler intrinsics for Digital Signal Processing Compiler support for European Telecommunications S Overflow and carry status flags for C and C++ code Texas Instruments (TI) C55x intrinsics for optimiz Compiler support for accessing registers using nam Pragmas recognized by the compiler Compiler and processor support for bit-banding Compiler type attribute, __attribute__((bitband)) --bitband compiler command-line option How the compiler handles bit-band objects placed o Compiler support for thread-local storage Compiler support for literal pools Compiler eight-byte alignment features Precompiled Header (PCH) files Automatic Precompiled Header (PCH) file processing Precompiled Header (PCH) file processing and the h Precompiled Header (PCH) file creation requirement Compilation with multiple Precompiled Header (PCH) Obsolete Precompiled Header (PCH) files Manually specifying the filename and location of a Selectively applying Precompiled Header (PCH) file Suppressing Precompiled Header (PCH) file processi Message output during Precompiled Header (PCH) pro Performance issues with Precompiled Header (PCH) f Default compiler options that are affected by opti Compiler Coding Practices Compiler Diagnostic Messages Using the Inline and Embedded Assemblers of the AR Compiler Command-line Options Language Extensions Compiler-specific Features C and C++ Implementation Details What is Semihosting? Via File Syntax Summary Table of GNU Language Extensions Standard C Implementation Definition Standard C++ Implementation Definition C and C++ Compiler Implementation Limits

Compiler eight-byte alignment features

3.20 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.
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