Re: [PATCH 06/15] mips: clear upper bits of FP registers on emulator writes

[Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>]

Hello.

On 01/27/2014 06:23 PM, Paul Burton wrote:

> The upper bits of an FP register are architecturally defined as
> unpredictable following an instructions which only writes the lower
> bits. The prior behaviour of the kernel is to leave them unmodified.
> This patch modifies that to clear the upper bits to zero. This is what
> the MSA architecture reference manual specifies should happen for its
> wider registers and is still permissible for scalar FP instructions
> given the bits unpredictability there.

> Signed-off-by: Paul Burton <paul.burton@imgtec.com>
> ---
>   arch/mips/math-emu/cp1emu.c | 25 ++++++++++++++++++++-----
>   1 file changed, 20 insertions(+), 5 deletions(-)

> diff --git a/arch/mips/math-emu/cp1emu.c b/arch/mips/math-emu/cp1emu.c
> index 9144842..c484f5f 100644
> --- a/arch/mips/math-emu/cp1emu.c
> +++ b/arch/mips/math-emu/cp1emu.c
> @@ -884,20 +884,35 @@ static inline int cop1_64bit(struct pt_regs *xcp)
>   } while (0)
>
>   #define SITOREG(si, x) do {						\
> -	if (cop1_64bit(xcp))						\
> +	if (cop1_64bit(xcp)) {						\
> +		unsigned i;						\
>   		set_fpr32(&ctx->fpr[x], 0, si);				\
> -	else								\
> +		for (i = 1; i < ARRAY_SIZE(ctx->fpr[x].val32); i++)	\
> +			set_fpr32(&ctx->fpr[x], i, 0);			\
> +	} else {							\
>   		set_fpr32(&ctx->fpr[(x) & ~1], (x) & 1, si);		\
> +	}								\
>   } while (0)
>
>   #define SIFROMHREG(si, x)	((si) = get_fpr32(&ctx->fpr[x], 1))
> -#define SITOHREG(si, x)		set_fpr32(&ctx->fpr[x], 1, si)
> +
> +#define SITOHREG(si, x) do {						\
> +	unsigned i;							\
> +	set_fpr32(&ctx->fpr[x], 1, si);					\
> +	for (i = 2; i < ARRAY_SIZE(ctx->fpr[x].val32); i++)		\
> +			set_fpr32(&ctx->fpr[x], i, 0);			\

    This line is over-indented, no? Compare the loop below...

> +} while (0)
>
>   #define DIFROMREG(di, x) \
>   	((di) = get_fpr64(&ctx->fpr[(x) & ~(cop1_64bit(xcp) == 0)], 0))
>
> -#define DITOREG(di, x) \
> -	set_fpr64(&ctx->fpr[(x) & ~(cop1_64bit(xcp) == 0)], 0, di)
> +#define DITOREG(di, x) do {						\
> +	unsigned fpr, i;						\
> +	fpr = (x) & ~(cop1_64bit(xcp) == 0);				\
> +	set_fpr64(&ctx->fpr[fpr], 0, di);				\
> +	for (i = 1; i < ARRAY_SIZE(ctx->fpr[x].val64); i++)		\
> +		set_fpr64(&ctx->fpr[fpr], i, 0);			\
> +} while (0)

WBR, Sergei