[PATCH v2 09/14] powerpc: Add NULLIFY_GPRS macros for register clears

[Christophe Leroy]

Le 08/08/2022 à 09:42, Andrew Donnellan a écrit :
> On Mon, 2022-07-25 at 16:29 +1000, Rohan McLure wrote:
>> Macros for restoring and saving registers to and from the stack
>> exist.
>> Provide macros with the same interface for clearing a range of gprs
>> by
>> setting each register's value in that range to zero.
>>
>> The resulting macros are called NULLIFY_GPRS and NULLIFY_NVGPRS,
>> keeping
>> with the naming of the accompanying restore and save macros, and
>> usage
>> of nullify to describe this operation elsewhere in the kernel.
>>
>> Signed-off-by: Rohan McLure <rmclure at linux.ibm.com>
>> ---
>> V1 -> V2: Change 'ZERO' usage in naming to 'NULLIFY', a more obvious
>> verb
> 
> And I see you've addressed my comment re 32 v 64 bit from V1 as well.
> 
> Reviewed-by: Andrew Donnellan <ajd at linux.ibm.com>
> 
>> ---
>>   arch/powerpc/include/asm/ppc_asm.h | 22 ++++++++++++++++++++++
>>   1 file changed, 22 insertions(+)
>>
>> diff --git a/arch/powerpc/include/asm/ppc_asm.h
>> b/arch/powerpc/include/asm/ppc_asm.h
>> index 83c02f5a7f2a..d6c46082bf7f 100644
>> --- a/arch/powerpc/include/asm/ppc_asm.h
>> +++ b/arch/powerpc/include/asm/ppc_asm.h
>> @@ -33,6 +33,20 @@
>>          .endr
>>   .endm
>>   
>> +/*
>> + * This expands to a sequence of register clears for regs start to
>> end
>> + * inclusive, of the form:
>> + *
>> + *   li rN, 0
>> + */
>> +.macro NULLIFY_REGS start, end
>> +       .Lreg=\start
>> +       .rept (\end - \start + 1)
>> +       li      .Lreg, 0
>> +       .Lreg=.Lreg+1
>> +       .endr
>> +.endm
>> +
> 
> I suppose this could be done using the existing OP_REGS macro,
> something like OP_REGS li, 0, start, end, 0, 0 - but a load immediate
> is semantically a bit different from the existing uses of OP_REGS so I
> don't mind either way

Not sure it would work. You'd get:

	li	.Lreg, 0 + 0 * .Lreg(0)


Even if it works that would be odd.

> 
>>   /*
>>    * Macros for storing registers into and loading registers from
>>    * exception frames.
>> @@ -49,6 +63,14 @@
>>   #define REST_NVGPRS(base)              REST_GPRS(13, 31, base)
>>   #endif
>>   
>> +#define        NULLIFY_GPRS(start, end)        NULLIFY_REGS start,
>> end
>> +#ifdef __powerpc64__
>> +#define        NULLIFY_NVGPRS()                NULLIFY_GPRS(14, 31)
>> +#else
>> +#define        NULLIFY_NVGPRS()                NULLIFY_GPRS(13, 31)
>> +#endif
>> +#define        NULLIFY_GPR(n)                  NULLIFY_GPRS(n, n)
>> +
>>   #define SAVE_GPR(n, base)              SAVE_GPRS(n, n, base)
>>   #define REST_GPR(n, base)              REST_GPRS(n, n, base)
>>   
>