Re: [Xen-devel] [PATCH 4/4] xen/arm: Add some useful debug in coprocessor trapping

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-04-24 at 23:45 +0100, Julien Grall wrote:
> XSA-93 adds a couple of new functions to trap coprocessor registers. They
> unconditonally inject an undefined instruction to guest.

"unconditionally"

> When debugging an OS at early stage, it may be hard to know why the guest
> received an UNDEFINED. Add some debug message to help the developper when Xen

"developer"

> is built in debug mode.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> ---
>  xen/arch/arm/traps.c            |   18 ++++++++++++++++++
>  xen/include/asm-arm/processor.h |   15 +++++++++++++--
>  2 files changed, 31 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index 1f61e6e..c04f53f 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -1539,23 +1539,41 @@ bad_cp:
>  
>  static void do_cp14_dbg(struct cpu_user_regs *regs, union hsr hsr)
>  {
> +    struct hsr_cp64 cp64 = hsr.cp64;

Won't this be unused in debug=n builds and therefore not build?

> diff --git a/xen/include/asm-arm/processor.h b/xen/include/asm-arm/processor.h
> index 9267c1b..bc29de1 100644
> --- a/xen/include/asm-arm/processor.h
> +++ b/xen/include/asm-arm/processor.h
> @@ -289,12 +289,23 @@ union hsr {
>          unsigned long reg2:5;   /* Rt2 */
>          unsigned long sbzp2:1;
>          unsigned long op1:4;    /* Op1 */
> -        unsigned long cc:4;     /* Condition Code */
> -        unsigned long ccvalid:1;/* CC Valid */
> +        unsigned long cc:4;     /* condition code */
> +        unsigned long ccvalid:1;/* cc valid */

This seems a bit gratuitous, especially given it appears 3 times and you
only change one. I'd prefer if you just made the new version match the
existing ones than change everything.

>          unsigned long len:1;    /* Instruction length */
>          unsigned long ec:6;     /* Exception Class */
>      } cp64; /* HSR_EC_CP15_64, HSR_EC_CP14_64 */
>  
> +    struct hsr_cp {
> +        unsigned long coproc:4; /* Number of coproc accessed */
> +        unsigned long sbz0p:1;
> +        unsigned long tas:1;    /* Trapped Advanced SIMD */
> +        unsigned long res0:14;
> +        unsigned long cc:4;     /* condition code */
> +        unsigned long ccvalid:1;/* cc valid */
> +        unsigned long len:1;    /* Instruction length */
> +        unsigned long ec:6;     /* Exception Class */
> +    } cp; /* HSR_EC_CP */
> +
>  #ifdef CONFIG_ARM_64
>      struct hsr_sysreg {
>          unsigned long read:1;   /* Direction */



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