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SubjectRe: [PATCH v6 1/6] arm64: Add HAVE_REGS_AND_STACK_ACCESS_API feature
On 05/21/15 13:55, Catalin Marinas wrote:
> On Wed, May 20, 2015 at 11:29:24PM -0400, David Long wrote:
>> On 05/20/15 09:39, Catalin Marinas wrote:
>>> On Mon, Apr 20, 2015 at 04:19:42PM -0400, David Long wrote:
>>>> diff --git a/arch/arm64/include/uapi/asm/ptrace.h b/arch/arm64/include/uapi/asm/ptrace.h
>>>> index 6913643..58c0223 100644
>>>> --- a/arch/arm64/include/uapi/asm/ptrace.h
>>>> +++ b/arch/arm64/include/uapi/asm/ptrace.h
>>>> @@ -61,6 +61,42 @@
>>>>
>>>> #ifndef __ASSEMBLY__
>>>>
>>>> +#define ARM_pstate pstate
>>>> +#define ARM_pc pc
>>>> +#define ARM_sp sp
>>>> +#define ARM_lr regs[30]
>>>> +#define ARM_fp 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_ip1 regs[17]
>>>> +#define ARM_ip0 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]
>>>> +#define ARM_ORIG_x0 orig_x0
>>>
>>> I replied some time ago on this part. I don't see the point these
>>> macros.
>>
>> I replied belatedly on April 20 saying what I did matches (more or less) how
>> it's done on various other platforms, including arm and powerpc.
>> It looks like this comes from the pt_regs structure defining the
>> registers as an array instead of a list of structure fields. It looks
>> to me like that design choice is pretty widely depended upon now and
>> would be quite disruptive to change. It also seems to me a relatively
>> clean way to do it on systems with a uniform register set.
>
> I see why we need to cope with the regs[] array but why do we need these
> definitions in a uapi file?
>

I expect Sandeepa did it that way because it's the way it's done in
other architectures. I see your point though, these definitions are
only referenced in a macro that's defined and used only in ptrace.c. I
can easily move them there.

>>>> +
>>>> /*
>>>> * User structures for general purpose, floating point and debug registers.
>>>> */
>>>> diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
>>>> index d882b83..a889f79 100644
>>>> --- a/arch/arm64/kernel/ptrace.c
>>>> +++ b/arch/arm64/kernel/ptrace.c
>>>> @@ -48,6 +48,122 @@
>>>> #define CREATE_TRACE_POINTS
>>>> #include <trace/events/syscalls.h>
>>>>
>>>> +struct pt_regs_offset {
>>>> + const char *name;
>>>> + int offset;
>>>> +};
>>>> +
>>>> +#define REG_OFFSET_NAME(r) \
>>>> + {.name = #r, .offset = offsetof(struct pt_regs, ARM_##r)}
>>
>>> Can you not just use "offsetof(struct pt_regs, r)" here? That would be
>>> the same as x86, powerpc.
>>
>> The registers (except for pc, pstate, and sp) are not separate structure
>> fields, they are slots in a single array. To reference them the symbolic
>> name has to be converted to an index (integer register number) somehow.
>
> Can we not keep them local to this file, say __reg_x0 etc. (something to
> make it clear they are for internal use)?
>

As above we can make it local to the file. Given that I don't think
there's a need to chance ARM_x* to __reg_x* though, is there? Either
way, no problem.

-dl



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