Re: UNALIGNED_MEMCPY

[Denis Ovsienko <denis () ovsienko info>]

On Wed, 13 May 2026 15:58:51 -0700
Guy Harris <gharris () sonic net> wrote:

> I'm not sure about 32-bit Arm, though. It may be that the 32-bit Arm
> platforms that matter do handle unaligned loads.

On Raspberry Pi 0 (armv6l):

# echo 1 >/proc/cpu/alignment

kernel: alignment: ignoring faults is unsafe on this CPU. Defaulting to
fixup mode.

# cat /proc/cpu/alignment 
User:           0
System:         0 (0x0)
Skipped:        0
Half:           0
Word:           0
DWord:          0
Multi:          0
User faults:    3 (fixup+warn)

Yet setting this to 4 (signal) and running a test program that triggers
a signal on SPARC neither triggers the signal nor increments the fault
counter on armv6l.  The same holds for armv7l, if I remember correctly.

Maybe I am not testing it right, or maybe the problem no longer exists.
The next step to clarify this could be to performance-test aligned and
unaligned loads on a few architectures, and to see if there is a
meaningful difference in that sense.

-- 
    Denis Ovsienko
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