Re: [Xen-devel] [RFC 08/16] xen/arm: arm64: Reserve a brk immediate to fault on purpose

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 5 May 2016, Julien Grall wrote:
> It may not possible to return a proper error when encoding an
> instruction. Instead, a handcrafted instruction will be returned.
> 
> Also, provide the encoding for the faulting instruction.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


>  xen/include/asm-arm/arm64/brk.h | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/xen/include/asm-arm/arm64/brk.h b/xen/include/asm-arm/arm64/brk.h
> index 7867b07..04442c4 100644
> --- a/xen/include/asm-arm/arm64/brk.h
> +++ b/xen/include/asm-arm/arm64/brk.h
> @@ -12,8 +12,21 @@
>  /*
>   * #imm16 values used for BRK instruction generation
>   * 0x001: xen-mode BUG() and WARN() traps
> + * 0x002: for triggering a fault on purpose (reserved)
>   */
>  #define BRK_BUG_FRAME_IMM   1
> +#define BRK_FAULT_IMM       2
> +
> +/*
> + * BRK instruction encoding
> + * The #imm16 value should be placed at bits[20:5] within BRK ins
> + */
> +#define AARCH64_BREAK_MON 0xd4200000
> +
> +/*
> + * BRK instruction for provoking a fault on purpose
> + */
> +#define AARCH64_BREAK_FAULT (AARCH64_BREAK_MON | (BRK_FAULT_IMM << 5))
>  
>  #endif /* !__ASM_ARM_ARM64_BRK */
>  /*
> -- 
> 1.9.1
> 

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