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

[Nick Hudson <nick.hudson%gmx.co.uk@localhost>]

On 06/01/2019 08:46, Rin Okuyama wrote:
> (CC added to port-arm%NetBSD.org@localhost)
>
> Let me summarize the problem briefly. In axe(4), there is a code where
> memcpy() is carried out from 2-byte aligned buffer to 4-byte structure:
>
> https://nxr.netbsd.org/xref/src/sys/dev/usb/if_axe.c#1284
>
> This results in kernel panic due to alignment fault on earmv[67]hf:
>
> https://twitter.com/furandon_pig/status/1071771151418908672
>
> In short, this is because -munaligned-access is enabled on ARMv6+ by
> default for GCC. As the unaligned memory access is forbidden in the
> supervisor mode unlike in the user mode, we need to explicitly specify
> -mno-unaligned-access for kernel on ARMv6+.


I'm pretty sure this is the same as http://gnats.netbsd.org/50038

Maybe I should be brave enough to stop using PMAP_NOCACHE in bus_dma.c 
for armv6+ and fix any missing bus_dmamap_sync calls.

Nick