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

David Long
2015-08-13T03:50:53Z

On 08/11/15 13:31, Will Deacon wrote:
> 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?

Yes, "offsetof" actually though. I've just made that change.

>> +
>> #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?

If I understand the question I think it's fine that it only deals with
kernel-mode registers. The implemenation is functionally similar to the
other five architectures that implement it.

>> +
>> +/* 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.

OK, I've ripped that out and replaced REG_OFFSET_NAME with
GPR_OFFSET_NAME, for the numbered registers. I'm using REGS_OFFSET_NAME
(defined for all architectures in my earlier cleanup patch) for the
non-numbered registers.

>
>> +
>> +#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).
>

Possibly, I can test that when I'm back from my short vacation this
week. The lr/x30 thing seems to be a recurring issue. Perhaps it is
best simply to add a reundant entry for x30 as "lr". It's simple enough
to do, although just slightly ugly looking as it would have to be done
without a macro. Would one ever use "x31" in place of "sp"?

Conversions in the other direction would have to use one or the other of
course.

> Will
>

-dl