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

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Message-Id: <20240216073315.3801833-1-linux@roeck-us.net>
Date: Thu, 15 Feb 2024 23:33:15 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Helge Deller <deller@....de>
Cc: linux-parisc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Guenter Roeck <linux@...ck-us.net>
Subject: [PATCH] parisc/unaligned: Rewrite 64-bit inline assembly of emulate_ldd()

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) );
 #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);
-- 
2.39.2