Re: [PATCH v7 08/37] nds32: Exception handling

[Arnd Bergmann <arnd@arndb.de>]

On Tue, Feb 13, 2018 at 10:09 AM, Greentime Hu <green.hu@gmail.com> wrote:
> This patch includes the exception/interrupt entries, pt_reg structure and
> related accessors.
>
> /* Unaligned accessing handling*/
> Andes processors cannot load/store information which is not naturally
> aligned on the bus, i.e., loading a 4 byte data whose start address must
> be divisible by 4. If unaligned data accessing is happened, data
> unaligned exception will be triggered and user will get SIGSEGV or
> kernel oops according to the unaligned address. In order to make user be
> able to load/store data from an unaligned address, software load/store
> emulation is implemented in arch/nds32/mm/alignment.c to address data
> unaligned exception.
>
> Unaligned accessing handling is disabled by default because it is not a
> normal case. User can enable this feature by following steps.
>
> A. Compile time:
>     1. Enable kernel config CONFIG_ALIGNMENT_TRAP
> B. Run time:
>     1. Enter /proc/sys/nds32/unaligned_acess folder
>     2. Write 1 to file enable_mode to enable unaligned accessing
>        handling. User can disable it by writing 0 to this file.
>     3. Write 1 to file debug to show which unaligned address is under
>        processing. User can disable it by writing 0 to this file.
>
> However, unaligned accessing handler cannot work if this unaligned
> address is not accessible such as protection violation. On this
> condition, the default behaviors for addressing data unaligned exception
> still happen
>
> Signed-off-by: Vincent Chen <vincentc@andestech.com>
> Signed-off-by: Greentime Hu <greentime@andestech.com>

Acked-by: Arnd Bergmann <arnd@arndb.de>