Christophe Leroy [off-list ref] writes:

Hi Michael,

I see this patch is marked as "defered" in patchwork, but I can't see 
any related discussion. Is it normal ?

Because it uses the "m<>" constraint which didn't work on GCC 4.6.

https://github.com/linuxppc/issues/issues/297

So we should be able to pick it up for v5.9 hopefully.

cheers

Le 16/04/2020 à 14:39, Christophe Leroy a écrit :

quoted

At the time being, __put_user()/__get_user() and friends only use
D-form addressing, with 0 offset. Ex:

	lwz	reg1, 0(reg2)

Give the compiler the opportunity to use other adressing modes
whenever possible, to get more optimised code.

Hereunder is a small exemple:

struct test {
	u32 item1;
	u16 item2;
	u8 item3;
	u64 item4;
};

int set_test_user(struct test __user *from, struct test __user *to)
{
	int err;
	u32 item1;
	u16 item2;
	u8 item3;
	u64 item4;

	err = __get_user(item1, &from->item1);
	err |= __get_user(item2, &from->item2);
	err |= __get_user(item3, &from->item3);
	err |= __get_user(item4, &from->item4);

	err |= __put_user(item1, &to->item1);
	err |= __put_user(item2, &to->item2);
	err |= __put_user(item3, &to->item3);
	err |= __put_user(item4, &to->item4);

	return err;
}

Before the patch:

00000df0 <set_test_user>:
  df0:	94 21 ff f0 	stwu    r1,-16(r1)
  df4:	39 40 00 00 	li      r10,0
  df8:	93 c1 00 08 	stw     r30,8(r1)
  dfc:	93 e1 00 0c 	stw     r31,12(r1)
  e00:	7d 49 53 78 	mr      r9,r10
  e04:	80 a3 00 00 	lwz     r5,0(r3)
  e08:	38 e3 00 04 	addi    r7,r3,4
  e0c:	7d 46 53 78 	mr      r6,r10
  e10:	a0 e7 00 00 	lhz     r7,0(r7)
  e14:	7d 29 33 78 	or      r9,r9,r6
  e18:	39 03 00 06 	addi    r8,r3,6
  e1c:	7d 46 53 78 	mr      r6,r10
  e20:	89 08 00 00 	lbz     r8,0(r8)
  e24:	7d 29 33 78 	or      r9,r9,r6
  e28:	38 63 00 08 	addi    r3,r3,8
  e2c:	7d 46 53 78 	mr      r6,r10
  e30:	83 c3 00 00 	lwz     r30,0(r3)
  e34:	83 e3 00 04 	lwz     r31,4(r3)
  e38:	7d 29 33 78 	or      r9,r9,r6
  e3c:	7d 43 53 78 	mr      r3,r10
  e40:	90 a4 00 00 	stw     r5,0(r4)
  e44:	7d 29 1b 78 	or      r9,r9,r3
  e48:	38 c4 00 04 	addi    r6,r4,4
  e4c:	7d 43 53 78 	mr      r3,r10
  e50:	b0 e6 00 00 	sth     r7,0(r6)
  e54:	7d 29 1b 78 	or      r9,r9,r3
  e58:	38 e4 00 06 	addi    r7,r4,6
  e5c:	7d 43 53 78 	mr      r3,r10
  e60:	99 07 00 00 	stb     r8,0(r7)
  e64:	7d 23 1b 78 	or      r3,r9,r3
  e68:	38 84 00 08 	addi    r4,r4,8
  e6c:	93 c4 00 00 	stw     r30,0(r4)
  e70:	93 e4 00 04 	stw     r31,4(r4)
  e74:	7c 63 53 78 	or      r3,r3,r10
  e78:	83 c1 00 08 	lwz     r30,8(r1)
  e7c:	83 e1 00 0c 	lwz     r31,12(r1)
  e80:	38 21 00 10 	addi    r1,r1,16
  e84:	4e 80 00 20 	blr

After the patch:

00000dbc <set_test_user>:
  dbc:	39 40 00 00 	li      r10,0
  dc0:	7d 49 53 78 	mr      r9,r10
  dc4:	80 03 00 00 	lwz     r0,0(r3)
  dc8:	7d 48 53 78 	mr      r8,r10
  dcc:	a1 63 00 04 	lhz     r11,4(r3)
  dd0:	7d 29 43 78 	or      r9,r9,r8
  dd4:	7d 48 53 78 	mr      r8,r10
  dd8:	88 a3 00 06 	lbz     r5,6(r3)
  ddc:	7d 29 43 78 	or      r9,r9,r8
  de0:	7d 48 53 78 	mr      r8,r10
  de4:	80 c3 00 08 	lwz     r6,8(r3)
  de8:	80 e3 00 0c 	lwz     r7,12(r3)
  dec:	7d 29 43 78 	or      r9,r9,r8
  df0:	7d 43 53 78 	mr      r3,r10
  df4:	90 04 00 00 	stw     r0,0(r4)
  df8:	7d 29 1b 78 	or      r9,r9,r3
  dfc:	7d 43 53 78 	mr      r3,r10
  e00:	b1 64 00 04 	sth     r11,4(r4)
  e04:	7d 29 1b 78 	or      r9,r9,r3
  e08:	7d 43 53 78 	mr      r3,r10
  e0c:	98 a4 00 06 	stb     r5,6(r4)
  e10:	7d 23 1b 78 	or      r3,r9,r3
  e14:	90 c4 00 08 	stw     r6,8(r4)
  e18:	90 e4 00 0c 	stw     r7,12(r4)
  e1c:	7c 63 53 78 	or      r3,r3,r10
  e20:	4e 80 00 20 	blr

Signed-off-by: Christophe Leroy <redacted>
Reviewed-by: Segher Boessenkool <redacted>
---
v2:
- Added <> modifier in __put_user_asm() and __get_user_asm()
- Removed %U2 in __put_user_asm2() and __get_user_asm2()
- Reworded the commit log
---
  arch/powerpc/include/asm/uaccess.h | 28 ++++++++++++++--------------
  1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index 7c811442b607..9365b59495a2 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h

@@ -114,7 +114,7 @@ extern long __put_user_bad(void);
   */
  #define __put_user_asm(x, addr, err, op)			\
  	__asm__ __volatile__(					\
-		"1:	" op " %1,0(%2)	# put_user\n"		\
+		"1:	" op "%U2%X2 %1,%2	# put_user\n"	\
  		"2:\n"						\
  		".section .fixup,\"ax\"\n"			\
  		"3:	li %0,%3\n"				\

@@ -122,7 +122,7 @@ extern long __put_user_bad(void);
  		".previous\n"					\
  		EX_TABLE(1b, 3b)				\
  		: "=r" (err)					\
-		: "r" (x), "b" (addr), "i" (-EFAULT), "0" (err))
+		: "r" (x), "m<>" (*addr), "i" (-EFAULT), "0" (err))
  
  #ifdef __powerpc64__
  #define __put_user_asm2(x, ptr, retval)				\

@@ -130,8 +130,8 @@ extern long __put_user_bad(void);
  #else /* __powerpc64__ */
  #define __put_user_asm2(x, addr, err)				\
  	__asm__ __volatile__(					\
-		"1:	stw %1,0(%2)\n"				\
-		"2:	stw %1+1,4(%2)\n"			\
+		"1:	stw%X2 %1,%2\n"			\
+		"2:	stw%X2 %L1,%L2\n"			\
  		"3:\n"						\
  		".section .fixup,\"ax\"\n"			\
  		"4:	li %0,%3\n"				\

@@ -140,7 +140,7 @@ extern long __put_user_bad(void);
  		EX_TABLE(1b, 4b)				\
  		EX_TABLE(2b, 4b)				\
  		: "=r" (err)					\
-		: "r" (x), "b" (addr), "i" (-EFAULT), "0" (err))
+		: "r" (x), "m" (*addr), "i" (-EFAULT), "0" (err))
  #endif /* __powerpc64__ */
  
  #define __put_user_size_allowed(x, ptr, size, retval)		\

@@ -260,7 +260,7 @@ extern long __get_user_bad(void);
  
  #define __get_user_asm(x, addr, err, op)		\
  	__asm__ __volatile__(				\
-		"1:	"op" %1,0(%2)	# get_user\n"	\
+		"1:	"op"%U2%X2 %1, %2	# get_user\n"	\
  		"2:\n"					\
  		".section .fixup,\"ax\"\n"		\
  		"3:	li %0,%3\n"			\

@@ -269,7 +269,7 @@ extern long __get_user_bad(void);
  		".previous\n"				\
  		EX_TABLE(1b, 3b)			\
  		: "=r" (err), "=r" (x)			\
-		: "b" (addr), "i" (-EFAULT), "0" (err))
+		: "m<>" (*addr), "i" (-EFAULT), "0" (err))
  
  #ifdef __powerpc64__
  #define __get_user_asm2(x, addr, err)			\

@@ -277,8 +277,8 @@ extern long __get_user_bad(void);
  #else /* __powerpc64__ */
  #define __get_user_asm2(x, addr, err)			\
  	__asm__ __volatile__(				\
-		"1:	lwz %1,0(%2)\n"			\
-		"2:	lwz %1+1,4(%2)\n"		\
+		"1:	lwz%X2 %1, %2\n"			\
+		"2:	lwz%X2 %L1, %L2\n"		\
  		"3:\n"					\
  		".section .fixup,\"ax\"\n"		\
  		"4:	li %0,%3\n"			\

@@ -289,7 +289,7 @@ extern long __get_user_bad(void);
  		EX_TABLE(1b, 4b)			\
  		EX_TABLE(2b, 4b)			\
  		: "=r" (err), "=&r" (x)			\
-		: "b" (addr), "i" (-EFAULT), "0" (err))
+		: "m" (*addr), "i" (-EFAULT), "0" (err))
  #endif /* __powerpc64__ */
  
  #define __get_user_size_allowed(x, ptr, size, retval)		\

@@ -299,10 +299,10 @@ do {								\
  	if (size > sizeof(x))					\
  		(x) = __get_user_bad();				\
  	switch (size) {						\
-	case 1: __get_user_asm(x, ptr, retval, "lbz"); break;	\
-	case 2: __get_user_asm(x, ptr, retval, "lhz"); break;	\
-	case 4: __get_user_asm(x, ptr, retval, "lwz"); break;	\
-	case 8: __get_user_asm2(x, ptr, retval);  break;	\
+	case 1: __get_user_asm(x, (u8 __user *)ptr, retval, "lbz"); break;	\
+	case 2: __get_user_asm(x, (u16 __user *)ptr, retval, "lhz"); break;	\
+	case 4: __get_user_asm(x, (u32 __user *)ptr, retval, "lwz"); break;	\
+	case 8: __get_user_asm2(x, (u64 __user *)ptr, retval);  break;	\
  	default: (x) = __get_user_bad();			\
  	}							\
  } while (0)