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

Will Deacon
2015-08-11T17:31:30Z

Hi David,

On Tue, Aug 11, 2015 at 01:52:38AM +0100, David Long wrote:
> From: "David A. Long" <dave.long@linaro.org>
>
> Add HAVE_REGS_AND_STACK_ACCESS_API feature for arm64.
>
> Signed-off-by: David A. Long <dave.long@linaro.org>
> ---
> 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