Alignment

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Arm^® Compiler Migration and Compatibility Guide

Version 6.16

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5.11 Alignment

Data and code must be aligned to appropriate boundaries.

For example, The T32 pseudo-instruction ADR can only load addresses that are word aligned, but a label within T32 code might not be word aligned. You must use an alignment directive to ensure four-byte alignment of an address within T32 code.

An alignment directive aligns the current location to a specified boundary by padding with zeros or NOP instructions.

Note:

The integrated assembler sets a minimum alignment of 4 bytes for a .text section. However, if you define your own sections with the integrated assembler, then you must include the .balign directive to set the correct alignment. For a section containing T32 instructions, set the alignment to 2 bytes. For a section containing A32 instructions, set the alignment to 4 bytes.

armasm syntax

armasm syntax assembly provides the ALIGN n directive, where n specifies the alignment boundary in bytes. For example, the directive ALIGN 128 aligns addresses to 128-byte boundaries.

armasm syntax assembly also provides the PRESERVE8 directive. The PRESERVE8 directive specifies that the current file preserves eight-byte alignment of the stack.

GNU syntax

GNU syntax assembly provides the .balign n directive, which uses the same format as ALIGN.

Convert all instances of ALIGN n to .balign n.

Note:

GNU syntax assembly also provides the

.align
						n

directive. However, the format of n varies from system to system. The .balign directive provides the same alignment functionality as .align with a consistent behavior across all architectures.

Convert all instances of PRESERVE8 to .eabi_attribute Tag_ABI_align_preserved, 1.