Re: Unaligned access in kernel on ARMv6+ (Re: CVS commit: src/sys/dev/usb)

To: Greg Troxel <gdt%lexort.com@localhost>
Subject: Re: Unaligned access in kernel on ARMv6+ (Re: CVS commit: src/sys/dev/usb)
From: Martin Husemann <martin%duskware.de@localhost>
Date: Sun, 6 Jan 2019 14:36:19 +0100

On Sun, Jan 06, 2019 at 08:31:53AM -0500, Greg Troxel wrote:
> Why do we generate code with unaligned access in user space?  That seems
> surprising, if the processor isn't happy about it.

The processor is happy with it, both in user- and kernel space.
Only special memory regions mapped uncached make it trap.

Nick suggest to change the mapping for bus_dma to cached, which would avoid
the issue but may expose bugs in device drivers.

Martin

Follow-Ups:
- Re: Unaligned access in kernel on ARMv6+ (Re: CVS commit: src/sys/dev/usb)
  - From: Jason Thorpe

References:
- re: Unaligned access in kernel on ARMv6+ (Re: CVS commit: src/sys/dev/usb)
  - From: matthew green
- Re: Unaligned access in kernel on ARMv6+ (Re: CVS commit: src/sys/dev/usb)
  - From: Greg Troxel

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