linux-kernel - Re: [PATCH v12 01/10] arm64: Add HAVE_REGS_AND_STACK_ACCESS

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Date:	Thu, 28 Apr 2016 17:08:51 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	David Long <dave.long@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Sandeepa Prabhu <sandeepa.s.prabhu@...il.com>,
	William Cohen <wcohen@...hat.com>,
	Pratyush Anand <panand@...hat.com>,
	Steve Capper <steve.capper@...aro.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:	Dave P Martin <Dave.Martin@....com>,
	Mark Rutland <mark.rutland@....com>,
	Robin Murphy <Robin.Murphy@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Jens Wiklander <jens.wiklander@...aro.org>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Alex Bennée <alex.bennee@...aro.org>,
	Yang Shi <yang.shi@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"Suzuki K. Poulose" <suzuki.poulose@....com>,
	Kees Cook <keescook@...omium.org>,
	Zi Shen Lim <zlim.lnx@...il.com>,
	John Blackwood <john.blackwood@...r.com>,
	Feng Kan <fkan@....com>,
	Balamurugan Shanmugam <bshanmugam@....com>,
	James Morse <james.morse@....com>,
	Vladimir Murzin <Vladimir.Murzin@....com>,
	Mark Salyzyn <salyzyn@...roid.com>,
	Petr Mladek <pmladek@...e.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH v12 01/10] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API
 feature

On 27/04/16 19:52, David Long wrote:
> From: "David A. Long" <dave.long@...aro.org>
> 
> Add HAVE_REGS_AND_STACK_ACCESS_API feature for arm64.

And clearly a lot more.

> 
> Signed-off-by: David A. Long <dave.long@...aro.org>
> ---
>  arch/arm64/Kconfig              |   1 +
>  arch/arm64/include/asm/ptrace.h |  33 ++++++++++-
>  arch/arm64/kernel/ptrace.c      | 118 ++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 151 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 4f43622..8f662fd 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -80,6 +80,7 @@ config ARM64
>  	select HAVE_PERF_EVENTS
>  	select HAVE_PERF_REGS
>  	select HAVE_PERF_USER_STACK_DUMP
> +	select HAVE_REGS_AND_STACK_ACCESS_API
>  	select HAVE_RCU_TABLE_FREE
>  	select HAVE_SYSCALL_TRACEPOINTS
>  	select IOMMU_DMA if IOMMU_SUPPORT
> diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
> index a307eb6..ee02637 100644
> --- a/arch/arm64/include/asm/ptrace.h
> +++ b/arch/arm64/include/asm/ptrace.h
> @@ -119,6 +119,8 @@ struct pt_regs {
>  	u64 syscallno;
>  };
>  
> +#define MAX_REG_OFFSET offsetof(struct pt_regs, pstate)
> +
>  #define arch_has_single_step()	(1)
>  
>  #ifdef CONFIG_COMPAT
> @@ -147,6 +149,35 @@ struct pt_regs {
>  #define user_stack_pointer(regs) \
>  	(!compat_user_mode(regs) ? (regs)->sp : (regs)->compat_sp)
>  
> +extern int regs_query_register_offset(const char *name);
> +extern const char *regs_query_register_name(unsigned int offset);
> +extern bool regs_within_kernel_stack(struct pt_regs *regs, unsigned long addr);
> +extern unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs,
> +					       unsigned int n);
> +
> +/**
> + * regs_get_register() - get register value from its offset
> + * @regs:	   pt_regs from which register value is gotten
> + * @offset:    offset number of the register.

Is it the offset? or the number?

> + *
> + * regs_get_register returns the value of a register whose offset from @regs.
> + * The @offset is the offset of the register in struct pt_regs.
> + * If @offset is bigger than MAX_REG_OFFSET, this returns 0.
> + */
> +static inline u64 regs_get_register(struct pt_regs *regs,
> +					      unsigned int offset)
> +{
> +	if (unlikely(offset > MAX_REG_OFFSET))
> +		return 0;
> +	return *(u64 *)((u64)regs + offset);

So clearly it is the offset. But is 3 a valid value? I don't think so.
How about something slightly more type safe:

	u64 val = 0;

	WARN_ON(offset & 7);

	offset >>= 3;
	switch (offset) {
	case	0 ... 30:
		val = regs->reg[offset];
		break;
	case	31:
		val = regs->sp;
		break;
	case	32:
		val = regs->pc;
		break;
	case	33:
 		val = regs->pstate;
		break;
	}

	return val;

I'm pretty sure you could replace 31/32/33 with macros using offsetof().
The compiler may even optimize this to something similar to what you
already have.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...