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

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Date: Fri, 16 Feb 2024 07:15:49 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Helge Deller <deller@....de>
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 05:48, Helge Deller wrote:
> 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!
> 
Confirmed working.

Thanks,
Guenter

> 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);
>