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In ARMv7-A and ARMv7-R, the A bit in the System Control Register (SCTLR) controls whether alignment checking is enabled or disabled. In ARMv7-M, the
UNALIGN_TRP bit, bit 3, in the Configuration and Control Register (CCR) controls this.
If alignment checking is enabled, all unaligned word and halfword
transfers cause an alignment exception. If disabled, unaligned accesses
are permitted for the
TBH instructions. Other data-accessing instructions
always cause an alignment exception for unaligned data.
specified address must be word-aligned.
If all your data accesses are aligned, you can use the
--no_unaligned_access command-line option to declare that the output
object was not permitted to make unaligned access. The linker can then avoid linking in any
library functions that support unaligned access if all input objects declare that they were
not permitted to use unaligned accesses.