linux-kernel - Re: [PATCH] ARM: hw_breakpoint: Add ARMv8 support

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Date:	Fri, 24 Jan 2014 15:57:52 +0000
From:	Will Deacon <will.deacon@....com>
To:	Christopher Covington <cov@...eaurora.org>
Cc:	Russell King <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: hw_breakpoint: Add ARMv8 support

Hi Christopher,

On Wed, Jan 22, 2014 at 06:29:25PM +0000, Christopher Covington wrote:
> Add the trivial support necessary to get hardware breakpoints
> working for GDB on ARMv8 simulators running in AArch32 mode.
> 
> Signed-off-by: Christopher Covington <cov@...eaurora.org>
> ---
>  arch/arm/include/asm/hw_breakpoint.h | 1 +
>  arch/arm/kernel/hw_breakpoint.c      | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/arch/arm/include/asm/hw_breakpoint.h b/arch/arm/include/asm/hw_breakpoint.h
> index eef55ea..8e427c7 100644
> --- a/arch/arm/include/asm/hw_breakpoint.h
> +++ b/arch/arm/include/asm/hw_breakpoint.h
> @@ -51,6 +51,7 @@ static inline void decode_ctrl_reg(u32 reg,
>  #define ARM_DEBUG_ARCH_V7_ECP14	3
>  #define ARM_DEBUG_ARCH_V7_MM	4
>  #define ARM_DEBUG_ARCH_V7_1	5
> +#define ARM_DEBUG_ARCH_V8	6
>  
>  /* Breakpoint */
>  #define ARM_BREAKPOINT_EXECUTE	0
> diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
> index 3d44660..45fbcaf 100644
> --- a/arch/arm/kernel/hw_breakpoint.c
> +++ b/arch/arm/kernel/hw_breakpoint.c
> @@ -257,6 +257,7 @@ static int enable_monitor_mode(void)
>  		break;
>  	case ARM_DEBUG_ARCH_V7_ECP14:
>  	case ARM_DEBUG_ARCH_V7_1:
> +	case ARM_DEBUG_ARCH_V8:
>  		ARM_DBG_WRITE(c0, c2, 2, (dscr | ARM_DSCR_MDBGEN));
>  		isb();
>  		break;

I'm slightly uneasy about this, mainly because I've not spent much time
looking at the AArch32 side of ARMv8 debug and I know that a fair amount
has changed since 7.1. Furthermore, the arch/arm/ kernel hasn't grown any v8
features yet and it's not clear whether that's a road down which people wish
to take it.

Anyway, assuming this works, can you please update debug_exception_updates_fsr
to return true for ARMv8 cores?

Will
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