Commit 42c782fa authored by Uros Bizjak's avatar Uros Bizjak Committed by Ingo Molnar
Browse files

x86/asm: Remove semicolon from "rep" prefixes 



Minimum version of binutils required to compile the kernel is 2.25.
This version correctly handles the "rep" prefixes, so it is possible
to remove the semicolon, which was used to support ancient versions
of GNU as.

Due to the semicolon, the compiler considers "rep; insn" (or its
alternate "rep\n\tinsn" form) as two separate instructions. Removing
the semicolon makes asm length calculations more accurate, consequently
making scheduling and inlining decisions of the compiler more accurate.

Removing the semicolon also enables assembler checks involving "rep"
prefixes. Trying to assemble e.g. "rep addl %eax, %ebx" results in:

  Error: invalid instruction `add' after `rep'

Signed-off-by: default avatarUros Bizjak <ubizjak@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pavel Machek <pavel@kernel.org>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Link: https://lore.kernel.org/r/20250418071437.4144391-2-ubizjak@gmail.com
parent 4850074f

arch/x86/include/asm/io.h

+3 −3
Original line number Diff line number Diff line
@@ -217,7 +217,7 @@ void memset_io(volatile void __iomem *, int, size_t); 
static inline void __iowrite32_copy(void __iomem *to, const void *from,

				    size_t count)

{

	asm volatile("rep ; movsl"

	asm volatile("rep movsl"

		     : "=&c"(count), "=&D"(to), "=&S"(from)

		     : "0"(count), "1"(to), "2"(from)

		     : "memory");
@@ -282,7 +282,7 @@ static inline void outs##bwl(u16 port, const void *addr, unsigned long count) \ 
			count--;					\

		}							\

	} else {							\

		asm volatile("rep; outs" #bwl				\

		asm volatile("rep outs" #bwl				\

			     : "+S"(addr), "+c"(count)			\

			     : "d"(port) : "memory");			\

	}								\
@@ -298,7 +298,7 @@ static inline void ins##bwl(u16 port, void *addr, unsigned long count) \ 
			count--;					\

		}							\

	} else {							\

		asm volatile("rep; ins" #bwl				\

		asm volatile("rep ins" #bwl				\

			     : "+D"(addr), "+c"(count)			\

			     : "d"(port) : "memory");			\

	}								\

arch/x86/include/asm/string_32.h

+6 −9
Original line number Diff line number Diff line
@@ -33,11 +33,11 @@ extern size_t strlen(const char *s); 
static __always_inline void *__memcpy(void *to, const void *from, size_t n)

{

	int d0, d1, d2;

	asm volatile("rep ; movsl\n\t"

	asm volatile("rep movsl\n\t"

		     "movl %4,%%ecx\n\t"

		     "andl $3,%%ecx\n\t"

		     "jz 1f\n\t"

		     "rep ; movsb\n\t"

		     "rep movsb\n\t"

		     "1:"

		     : "=&c" (d0), "=&D" (d1), "=&S" (d2)

		     : "0" (n / 4), "g" (n), "1" ((long)to), "2" ((long)from)
@@ -89,7 +89,7 @@ static __always_inline void *__constant_memcpy(void *to, const void *from, 
	if (n >= 5 * 4) {

		/* large block: use rep prefix */

		int ecx;

		asm volatile("rep ; movsl"

		asm volatile("rep movsl"

			     : "=&c" (ecx), "=&D" (edi), "=&S" (esi)

			     : "0" (n / 4), "1" (edi), "2" (esi)

			     : "memory"
@@ -165,8 +165,7 @@ extern void *memchr(const void *cs, int c, size_t count); 
static inline void *__memset_generic(void *s, char c, size_t count)

{

	int d0, d1;

	asm volatile("rep\n\t"

		     "stosb"

	asm volatile("rep stosb"

		     : "=&c" (d0), "=&D" (d1)

		     : "a" (c), "1" (s), "0" (count)

		     : "memory");
@@ -199,8 +198,7 @@ extern void *memset(void *, int, size_t); 
static inline void *memset16(uint16_t *s, uint16_t v, size_t n)

{

	int d0, d1;

	asm volatile("rep\n\t"

		     "stosw"

	asm volatile("rep stosw"

		     : "=&c" (d0), "=&D" (d1)

		     : "a" (v), "1" (s), "0" (n)

		     : "memory");
@@ -211,8 +209,7 @@ static inline void *memset16(uint16_t *s, uint16_t v, size_t n) 
static inline void *memset32(uint32_t *s, uint32_t v, size_t n)

{

	int d0, d1;

	asm volatile("rep\n\t"

		     "stosl"

	asm volatile("rep stosl"

		     : "=&c" (d0), "=&D" (d1)

		     : "a" (v), "1" (s), "0" (n)

		     : "memory");

arch/x86/kernel/head_32.S

+3 −5
Original line number Diff line number Diff line
@@ -86,7 +86,7 @@ SYM_CODE_START(startup_32) 
	movl $pa(__bss_stop),%ecx

	subl %edi,%ecx

	shrl $2,%ecx

	rep ; stosl

	rep stosl

/*

 * Copy bootup parameters out of the way.

 * Note: %esi still has the pointer to the real-mode data.
@@ -98,15 +98,13 @@ SYM_CODE_START(startup_32) 
	movl $pa(boot_params),%edi

	movl $(PARAM_SIZE/4),%ecx

	cld

	rep

	movsl

	rep movsl

	movl pa(boot_params) + NEW_CL_POINTER,%esi

	andl %esi,%esi

	jz 1f			# No command line

	movl $pa(boot_command_line),%edi

	movl $(COMMAND_LINE_SIZE/4),%ecx

	rep

	movsl

	rep movsl

1:



#ifdef CONFIG_OLPC

arch/x86/kernel/relocate_kernel_32.S

+3 −3
Original line number Diff line number Diff line
@@ -263,17 +263,17 @@ SYM_CODE_START_LOCAL_NOALIGN(swap_pages) 


	movl	%edx, %edi

	movl    $1024, %ecx

	rep ; movsl

	rep movsl



	movl	%ebp, %edi

	movl	%eax, %esi

	movl	$1024, %ecx

	rep ; movsl

	rep movsl



	movl	%eax, %edi

	movl	%edx, %esi

	movl	$1024, %ecx

	rep ; movsl

	rep movsl



	lea	PAGE_SIZE(%ebp), %esi

	jmp     0b

arch/x86/kernel/relocate_kernel_64.S

+3 −3
Original line number Diff line number Diff line
@@ -363,20 +363,20 @@ SYM_CODE_START_LOCAL_NOALIGN(swap_pages) 
	/* copy source page to swap page */

	movq	kexec_pa_swap_page(%rip), %rdi

	movl	$512, %ecx

	rep ; movsq

	rep movsq



	/* copy destination page to source page */

	movq	%rax, %rdi

	movq	%rdx, %rsi

	movl	$512, %ecx

	rep ; movsq

	rep movsq



	/* copy swap page to destination page */

	movq	%rdx, %rdi

	movq	kexec_pa_swap_page(%rip), %rsi

.Lnoswap:

	movl	$512, %ecx

	rep ; movsq

	rep movsq



	lea	PAGE_SIZE(%rax), %rsi

	jmp	.Lloop