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

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Date: Mon, 26 Feb 2024 21:18:02 +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 2/26/24 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@...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;
>>   	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"