linux-kernel - [RFC][PATCH 10/22] x86,uaccess: Remove .fixup usage

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Date:   Thu, 04 Nov 2021 17:47:39 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        jpoimboe@...hat.com, mark.rutland@....com, dvyukov@...gle.com,
        seanjc@...gle.com, pbonzini@...hat.com, mbenes@...e.cz
Subject: [RFC][PATCH 10/22] x86,uaccess: Remove .fixup usage

For the !CC_AS_ASM_GOTO_OUTPUT (aka. the legacy codepath), remove the
.fixup usage by employing both EX_TYPE_EFAULT_REG and EX_FLAG_CLR.
Like was already done for X86_32's version of __get_user_asm_u64()
use the "a" register for output, specifically so we can use CLR_AX.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/uaccess.h |   35 +++++++++++++++--------------------
 1 file changed, 15 insertions(+), 20 deletions(-)

--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -351,24 +351,22 @@ do {									\
 		     "1:	movl %[lowbits],%%eax\n"		\
 		     "2:	movl %[highbits],%%edx\n"		\
 		     "3:\n"						\
-		     ".section .fixup,\"ax\"\n"				\
-		     "4:	mov %[efault],%[errout]\n"		\
-		     "	xorl %%eax,%%eax\n"				\
-		     "	xorl %%edx,%%edx\n"				\
-		     "	jmp 3b\n"					\
-		     ".previous\n"					\
-		     _ASM_EXTABLE_UA(1b, 4b)				\
-		     _ASM_EXTABLE_UA(2b, 4b)				\
+		     _ASM_EXTABLE_TYPE_REG(1b, 3b, EX_TYPE_EFAULT_REG |	\
+					   EX_FLAG_CLR_AX_DX,		\
+					   %[errout])			\
+		     _ASM_EXTABLE_TYPE_REG(2b, 3b, EX_TYPE_EFAULT_REG |	\
+					   EX_FLAG_CLR_AX_DX,		\
+					   %[errout])			\
 		     : [errout] "=r" (retval),				\
 		       [output] "=&A"(x)				\
 		     : [lowbits] "m" (__m(__ptr)),			\
 		       [highbits] "m" __m(((u32 __user *)(__ptr)) + 1),	\
-		       [efault] "i" (-EFAULT), "0" (retval));		\
+		       "0" (retval));					\
 })
 
 #else
 #define __get_user_asm_u64(x, ptr, retval) \
-	 __get_user_asm(x, ptr, retval, "q", "=r")
+	 __get_user_asm(x, ptr, retval, "q", "=a")
 #endif
 
 #define __get_user_size(x, ptr, size, retval)				\
@@ -379,14 +377,14 @@ do {									\
 	__chk_user_ptr(ptr);						\
 	switch (size) {							\
 	case 1:								\
-		__get_user_asm(x_u8__, ptr, retval, "b", "=q");		\
+		__get_user_asm(x_u8__, ptr, retval, "b", "=a");		\
 		(x) = x_u8__;						\
 		break;							\
 	case 2:								\
-		__get_user_asm(x, ptr, retval, "w", "=r");		\
+		__get_user_asm(x, ptr, retval, "w", "=a");		\
 		break;							\
 	case 4:								\
-		__get_user_asm(x, ptr, retval, "l", "=r");		\
+		__get_user_asm(x, ptr, retval, "l", "=a");		\
 		break;							\
 	case 8:								\
 		__get_user_asm_u64(x, ptr, retval);			\
@@ -400,16 +398,13 @@ do {									\
 	asm volatile("\n"						\
 		     "1:	mov"itype" %[umem],%[output]\n"		\
 		     "2:\n"						\
-		     ".section .fixup,\"ax\"\n"				\
-		     "3:	mov %[efault],%[errout]\n"		\
-		     "	xorl %k[output],%k[output]\n"			\
-		     "	jmp 2b\n"					\
-		     ".previous\n"					\
-		     _ASM_EXTABLE_UA(1b, 3b)				\
+		     _ASM_EXTABLE_TYPE_REG(1b, 2b, EX_TYPE_EFAULT_REG | \
+					   EX_FLAG_CLR_AX,		\
+					   %[errout])			\
 		     : [errout] "=r" (err),				\
 		       [output] ltype(x)				\
 		     : [umem] "m" (__m(addr)),				\
-		       [efault] "i" (-EFAULT), "0" (err))
+		       "0" (err))
 
 #endif // CONFIG_CC_HAS_ASM_GOTO_OUTPUT