Re: [PATCH v8 1/7] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature

[Will Deacon]

Hi David,

On Tue, Aug 11, 2015 at 01:52:38AM +0100, David Long wrote:
> From: "David A. Long" <dave.long@xxxxxxxxxx>
> 
> Add HAVE_REGS_AND_STACK_ACCESS_API feature for arm64.
> 
> Signed-off-by: David A. Long <dave.long@xxxxxxxxxx>
> ---
>  arch/arm64/Kconfig              |  1 +
>  arch/arm64/include/asm/ptrace.h | 25 +++++++++++++
>  arch/arm64/kernel/ptrace.c      | 77 +++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 103 insertions(+)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 318175f..ef5d726 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -70,6 +70,7 @@ 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 IRQ_DOMAIN
> diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
> index d6dd9fd..8f440e9 100644
> --- a/arch/arm64/include/asm/ptrace.h
> +++ b/arch/arm64/include/asm/ptrace.h
> @@ -118,6 +118,8 @@ struct pt_regs {
>  	u64 syscallno;
>  };
>  
> +#define MAX_REG_OFFSET (sizeof(struct user_pt_regs) - sizeof(u64))

Can you not use offset_of(struct user_pt_regs, pstate) here?

> +
>  #define arch_has_single_step()	(1)
>  
>  #ifdef CONFIG_COMPAT
> @@ -146,6 +148,29 @@ struct pt_regs {
>  #define user_stack_pointer(regs) \
>  	(!compat_user_mode(regs) ? (regs)->sp : (regs)->compat_sp)
>  
> +/**
> + * regs_get_register() - get register value from its offset
> + * @regs:	   pt_regs from which register value is gotten
> + * @offset:    offset number of the register.
> + *
> + * 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);
> +}

Is this guaranteed only to be called on kernel-mode regs, or do we need
to deal with compat tasks too?

> +
> +/* Valid only for Kernel mode traps. */
> +static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
> +{
> +	return regs->sp;
> +}
> +
>  static inline unsigned long regs_return_value(struct pt_regs *regs)
>  {
>  	return regs->regs[0];
> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
> index d882b83..f6199a5 100644
> --- a/arch/arm64/kernel/ptrace.c
> +++ b/arch/arm64/kernel/ptrace.c
> @@ -48,6 +48,83 @@
>  #define CREATE_TRACE_POINTS
>  #include <trace/events/syscalls.h>
>  
> +#define ARM_pstate	pstate
> +#define ARM_pc		pc
> +#define ARM_sp		sp
> +#define ARM_x30		regs[30]
> +#define ARM_x29		regs[29]
> +#define ARM_x28		regs[28]
> +#define ARM_x27		regs[27]
> +#define ARM_x26		regs[26]
> +#define ARM_x25		regs[25]
> +#define ARM_x24		regs[24]
> +#define ARM_x23		regs[23]
> +#define ARM_x22		regs[22]
> +#define ARM_x21		regs[21]
> +#define ARM_x20		regs[20]
> +#define ARM_x19		regs[19]
> +#define ARM_x18		regs[18]
> +#define ARM_x17		regs[17]
> +#define ARM_x16		regs[16]
> +#define ARM_x15		regs[15]
> +#define ARM_x14		regs[14]
> +#define ARM_x13		regs[13]
> +#define ARM_x12		regs[12]
> +#define ARM_x11		regs[11]
> +#define ARM_x10		regs[10]
> +#define ARM_x9		regs[9]
> +#define ARM_x8		regs[8]
> +#define ARM_x7		regs[7]
> +#define ARM_x6		regs[6]
> +#define ARM_x5		regs[5]
> +#define ARM_x4		regs[4]
> +#define ARM_x3		regs[3]
> +#define ARM_x2		regs[2]
> +#define ARM_x1		regs[1]
> +#define ARM_x0		regs[0]

I've said it before, but I really don't like these macros. I'd rather
rework the following REG_OFFSET_NAME to be GPR_OFFSET_NAME which could
prefix the "x" in the name field.

> +
> +#define REG_OFFSET_NAME(r) \
> +	{.name = #r, .offset = offsetof(struct pt_regs, ARM_##r)}
> +#define REG_OFFSET_END {.name = NULL, .offset = 0}
> +
> +const struct pt_regs_offset regs_offset_table[] = {
> +	REG_OFFSET_NAME(x0),
> +	REG_OFFSET_NAME(x1),
> +	REG_OFFSET_NAME(x2),
> +	REG_OFFSET_NAME(x3),
> +	REG_OFFSET_NAME(x4),
> +	REG_OFFSET_NAME(x5),
> +	REG_OFFSET_NAME(x6),
> +	REG_OFFSET_NAME(x7),
> +	REG_OFFSET_NAME(x8),
> +	REG_OFFSET_NAME(x9),
> +	REG_OFFSET_NAME(x10),
> +	REG_OFFSET_NAME(x11),
> +	REG_OFFSET_NAME(x12),
> +	REG_OFFSET_NAME(x13),
> +	REG_OFFSET_NAME(x14),
> +	REG_OFFSET_NAME(x15),
> +	REG_OFFSET_NAME(x16),
> +	REG_OFFSET_NAME(x17),
> +	REG_OFFSET_NAME(x18),
> +	REG_OFFSET_NAME(x19),
> +	REG_OFFSET_NAME(x20),
> +	REG_OFFSET_NAME(x21),
> +	REG_OFFSET_NAME(x22),
> +	REG_OFFSET_NAME(x23),
> +	REG_OFFSET_NAME(x24),
> +	REG_OFFSET_NAME(x25),
> +	REG_OFFSET_NAME(x26),
> +	REG_OFFSET_NAME(x27),
> +	REG_OFFSET_NAME(x28),
> +	REG_OFFSET_NAME(x29),
> +	REG_OFFSET_NAME(x30),

Does this interact badly with perf tools, which expect to pass "lr" for
x30? (see tools/perf/arch/arm64/include/perf_regs.h).

Will
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