linux-kernel - Re: [PATCH] parisc/unaligned: Rewrite 64-bit inline assembly of emulate

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Date: Fri, 16 Feb 2024 14:48:04 +0100
From: Helge Deller <deller@....de>
To: Guenter Roeck <linux@...ck-us.net>
Cc: linux-parisc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] parisc/unaligned: Rewrite 64-bit inline assembly of
 emulate_ldd()

On 2/16/24 08:33, Guenter Roeck wrote:
> Convert to use real temp variables instead of clobbering processor
> registers.

Thanks for doing this.
It was on my todo list since quite some time :-)

> This aligns the 64-bit inline assembly code with the 32-bit
> assembly code which was rewritten with commit 427c1073a2a1
> ("parisc/unaligned: Rewrite 32-bit inline assembly of emulate_ldd()").
>
> While at it, fix comment in 32-bit rewrite code. Temporary variables are
> now used for both 32-bit and 64-bit code, so move their declarations
> to the function header.
>
> No functional change intended.
>
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
> Implemented while analyzing a bug. I am not really sure of it is worth
> the effort, but I figured that I might as well submit it.
>
>   arch/parisc/kernel/unaligned.c | 29 +++++++++++++----------------
>   1 file changed, 13 insertions(+), 16 deletions(-)
>
> diff --git a/arch/parisc/kernel/unaligned.c b/arch/parisc/kernel/unaligned.c
> index c520e551a165..622c7b549fb8 100644
> --- a/arch/parisc/kernel/unaligned.c
> +++ b/arch/parisc/kernel/unaligned.c
> @@ -169,7 +169,8 @@ static int emulate_ldw(struct pt_regs *regs, int toreg, int flop)
>   static int emulate_ldd(struct pt_regs *regs, int toreg, int flop)
>   {
>   	unsigned long saddr = regs->ior;
> -	__u64 val = 0;
> +	unsigned long shift;
> +	__u64 val = 0, temp1;

temp1 is ok to be "long".

>   	ASM_EXCEPTIONTABLE_VAR(ret);
>
>   	DPRINTF("load " RFMT ":" RFMT " to r%d for 8 bytes\n",
> @@ -180,25 +181,22 @@ static int emulate_ldd(struct pt_regs *regs, int toreg, int flop)
>
>   #ifdef CONFIG_64BIT
>   	__asm__ __volatile__  (
> -"	depd,z	%3,60,3,%%r19\n"		/* r19=(ofs&7)*8 */
> -"	mtsp	%4, %%sr1\n"
> -"	depd	%%r0,63,3,%3\n"
> -"1:	ldd	0(%%sr1,%3),%0\n"
> -"2:	ldd	8(%%sr1,%3),%%r20\n"
> -"	subi	64,%%r19,%%r19\n"
> -"	mtsar	%%r19\n"
> -"	shrpd	%0,%%r20,%%sar,%0\n"
> +"	depd,z	%4,60,3,%2\n"		/* shift=(ofs&7)*8 */
> +"	mtsp	%5, %%sr1\n"
> +"	depd	%%r0,63,3,%4\n"
> +"1:	ldd	0(%%sr1,%4),%0\n"
> +"2:	ldd	8(%%sr1,%4),%3\n"
> +"	subi	64,%2,%2\n"
> +"	mtsar	%2\n"
> +"	shrpd	%0,%3,%%sar,%0\n"
>   "3:	\n"
>   	ASM_EXCEPTIONTABLE_ENTRY_EFAULT(1b, 3b, "%1")
>   	ASM_EXCEPTIONTABLE_ENTRY_EFAULT(2b, 3b, "%1")
> -	: "=r" (val), "+r" (ret)
> -	: "0" (val), "r" (saddr), "r" (regs->isr)
> -	: "r19", "r20" );
> +	: "+r" (val), "+r" (ret), "=&r" (shift), "=&r" (temp1)
> +	: "r" (saddr), "r" (regs->isr) );

addr is actually being modified.
That's why I moved it into the output registers and
shuffled shift and temp1 one backwards, so that the registers
are now in the same ordering as on the 32-bit path.

I've pushed the modified patch here:
https://git.kernel.org/pub/scm/linux/kernel/git/deller/parisc-linux.git/commit/?h=for-next&id=a6ea53ce77e9dd6e388d673bdd4d80741f97b914

Please double-check!

Thanks!
Helge


>   #else
> -    {
> -	unsigned long shift, temp1;
>   	__asm__ __volatile__  (
> -"	zdep	%2,29,2,%3\n"		/* r19=(ofs&3)*8 */
> +"	zdep	%2,29,2,%3\n"		/* shift=(ofs&3)*8 */
>   "	mtsp	%5, %%sr1\n"
>   "	dep	%%r0,31,2,%2\n"
>   "1:	ldw	0(%%sr1,%2),%0\n"
> @@ -214,7 +212,6 @@ static int emulate_ldd(struct pt_regs *regs, int toreg, int flop)
>   	ASM_EXCEPTIONTABLE_ENTRY_EFAULT(3b, 4b, "%1")
>   	: "+r" (val), "+r" (ret), "+r" (saddr), "=&r" (shift), "=&r" (temp1)
>   	: "r" (regs->isr) );
> -    }
>   #endif
>
>   	DPRINTF("val = 0x%llx\n", val);