lkml.org 
[lkml]   [2018]   [Jan]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH v6 07/36] nds32: Exception handling
    2018-01-18 18:14 GMT+08:00 Arnd Bergmann <arnd@arndb.de>:
    > On Mon, Jan 15, 2018 at 6:53 AM, Greentime Hu <green.hu@gmail.com> wrote:
    >> From: Greentime Hu <greentime@andestech.com>
    >>
    >> This patch includes the exception/interrupt entries, pt_reg structure and
    >> related accessors.
    >>
    >> Signed-off-by: Vincent Chen <vincentc@andestech.com>
    >> Signed-off-by: Greentime Hu <greentime@andestech.com>
    >
    > Here it would be good to have a more detailed explanation about the alignment
    > trap handling. I remember discussing it with you before, but don't remember
    > the exact outcome. In particular you should explain here why you need to
    > handle alignment traps in the first place, and what the expected defaults
    > are (e.g. always disabled unless a user requests it, or always enabled) and
    > what kind of code runs into the traps (e.g. buggy kernel code, correct
    > kernel code, buggy user space code etc).
    >
    > Arnd


    Dear Arnd:

    I am plans to add the following description in the git commit's comment

    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 able to load/store data from an unaligned
    address, software load /store emulation is implemented in
    arch/nds32/mm/alignment.c to handle data unaligned exception.

    Unaligned accessing handling is disable by default because of it is not
    a normal case. User can follow the steps below to enable this feature.

    A. Compile time:
    1. Enable kernel config CONFIG_ALIGNMENT_TRAP
    B. Run time:
    1. Enter /proc/sys/nds32/unaligned_acess folder
    2.
    a. Write ‘1’ to file enable_mode to enable unaligned accessing handling
    for user space
    b. Write ‘2’ to file enable_mode to enable unaligned accessing handling
    for kernel space
    c. Write ‘3’ to file enable_mode to enable unaligned accessing handling
    for user and kernel space
    d. Write '0' to file enable_mode to disable all unaligned
    accessing handling
    3.
    a. Write ‘1’ to file debug to show which unaligned address is addressed
    b. Write ‘0’ to file debug to disable all information

    However, unaligned accessing handler can’t work on following conditions.
    A. The corresponding mode for unaligned address is not enabled.
    B. This unaligned address is not accessible such as protection violation.
    On these conditions, the default behaviors for data unaligned
    exception still happen.



    Thanks

    Vincent

    \
     
     \ /
      Last update: 2018-01-24 11:55    [W:3.678 / U:0.300 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site