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

[Andrew Donnellan <ajd@linux.ibm.com>]

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@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@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

>  /*
>   * 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)
>  

-- 
Andrew Donnellan    OzLabs, ADL Canberra
ajd@linux.ibm.com   IBM Australia Limited