Re: [PATCH] parisc/unaligned: Rewrite 64-bit inline assembly of emulate_ldd()

[Helge Deller]

On 2/26/24 20:29, Guenter Roeck wrote:
> Hi Helge,
>
> On Thu, Feb 15, 2024 at 11:33:15PM -0800, Guenter Roeck wrote:
> > Convert to use real temp variables instead of clobbering processor
> > registers. 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@xxxxxxxxxxxx>
> > ---
> > 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;
> >   	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) );
>
> It looks like something went wrong when this patch was applied.

I think this was my fault when I tried to reshuffle the input vars :-(

> It is now
>
> +"      depd,z  %4,60,3,%3\n"           /* shift=(ofs&7)*8 */
> ...
> +       : "+r" (val), "+r" (ret), "+r" (saddr), "=&r" (shift), "=&r" (temp1)
> +       : "r" (regs->isr) );
>
> meaning saddr is now %2, but the depd,z instruction
> still assumes it is %4. Unfortunately this results in a crash
> when trying to boot linux-next on parisc64.
>
> The patch below on top of linux-next fixes the problem for me.

I fixed it up with your hunk below in the parisc for-next branch, so it should be
fixed in linux-next soon.

THANKS!

Helge



> Guenter
>
> ---
> iff --git a/arch/parisc/kernel/unaligned.c b/arch/parisc/kernel/unaligned.c
> index 31974eddedc9..a8e75e5b884a 100644
> --- a/arch/parisc/kernel/unaligned.c
> +++ b/arch/parisc/kernel/unaligned.c
> @@ -181,7 +181,7 @@ static int emulate_ldd(struct pt_regs *regs, int toreg, int flop)
>
>   #ifdef CONFIG_64BIT
>          __asm__ __volatile__  (
> -"      depd,z  %4,60,3,%3\n"           /* shift=(ofs&7)*8 */
> +"      depd,z  %2,60,3,%3\n"           /* shift=(ofs&7)*8 */
>   "      mtsp    %5, %%sr1\n"
>   "      depd    %%r0,63,3,%2\n"
>   "1:    ldd     0(%%sr1,%2),%0\n"