Msg/MemoryMisaligned - Revision history

Henry at 04:07, 17 March 2019

2019-03-17T04:07:21Z

← Older revision		Revision as of 04:07, 17 March 2019
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	_start:		_start:
	ldw r2, 1(r0) # Load 4-byte word from a misaligned address		ldw r2, 1(r0) # Load 4-byte word from a misaligned address
			</syntaxhighlight>

			==== MIPS ====
			<syntaxhighlight lang="Asm" line highlight="3">
			.global _start
			_start:
			lw $v0, 1($0) # Load 4-byte word from a misaligned address
	</syntaxhighlight>		</syntaxhighlight>

Henry: /* Examples */

2019-03-10T07:07:44Z

Examples

← Older revision		Revision as of 07:07, 10 March 2019
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	==== ARMv7 ====		==== ARMv7 ====

	<syntaxhighlight lang="Asm" line highlight="11">		<syntaxhighlight lang="Asm" line highlight="3">
	.global _start		.global _start
	_start:		_start:
	ldr r0, [pc,#1] // Load 4-byte word from a misaligned address		ldr r0, [pc,#1] // Load 4-byte word from a misaligned address
	</syntaxhighlight>		</syntaxhighlight>

			==== Nios II ====
			<syntaxhighlight lang="Asm" line highlight="3">
			.global _start
			_start:
			ldw r2, 1(r0) # Load 4-byte word from a misaligned address
			</syntaxhighlight>

			The above examples try to load from an address that isn't a multiple of 4, but a 4-byte (word-sized) access must be to an address that is a multiple of 4 bytes. The warning message tells you the address the memory access attempted to access.

	=== Debugging ===		=== Debugging ===

Henry: Created page with "Memory accesses need to be aligned. The memory address must be a multiple of the size of the access. For example, a 4-byte load must use an address that is a multiple of 4 byt..."

2019-03-10T05:47:18Z

Created page with "Memory accesses need to be aligned. The memory address must be a multiple of the size of the access. For example, a 4-byte load must use an address that is a multiple of 4 byt..."

New page

Memory accesses need to be aligned. The memory address must be a multiple of the size of the access. For example, a 4-byte load must use an address that is a multiple of 4 bytes. This message says that the memory access was not properly aligned.

Attempting a misaligned memory access may throw an exception, or result in a load or store that doesn't behave as you would expect.

=== Examples ===
==== ARMv7 ====

<syntaxhighlight lang="Asm" line highlight="11">
.global _start
_start:
ldr r0, [pc,#1] // Load 4-byte word from a misaligned address
</syntaxhighlight>

=== Debugging ===
* Start by looking at the address used for the memory access (which base register and what offset). Then look at how the address is calculated and why it became incorrect.
* Also check that you are using the correct size memory access. For example, when iterating over a byte array (also called a "string"), each element is one byte, so a byte-sized load or store needs to be used.

=== Implementation ===
The simulator checks alignment for all memory accesses. This warning is generated while executing the load or store.

{{DisableMsg|Memory access misaligned}} If the processor throws an alignment exception, disabling the warning message does not change the behaviour of the processor, and the alignment exception will still be thrown.