From 0dcc51477b94d87f23aeb400b78fbdfb09363000 Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Fri, 18 Apr 2025 09:13:50 +0200 Subject: [PATCH] x86/boot: 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: Uros Bizjak Signed-off-by: Ingo Molnar Cc: Andy Lutomirski Cc: Brian Gerst Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Juergen Gross Cc: Kees Cook Cc: Linus Torvalds Cc: Martin Mares Cc: Peter Zijlstra Link: https://lore.kernel.org/r/20250418071437.4144391-1-ubizjak@gmail.com --- arch/x86/boot/bioscall.S | 4 ++-- arch/x86/boot/boot.h | 4 ++-- arch/x86/boot/compressed/string.c | 8 ++++---- arch/x86/boot/copy.S | 8 ++++---- arch/x86/boot/header.S | 2 +- arch/x86/boot/string.c | 2 +- arch/x86/boot/video.c | 2 +- 7 files changed, 15 insertions(+), 15 deletions(-) diff --git a/arch/x86/boot/bioscall.S b/arch/x86/boot/bioscall.S index aa9b964575843..cf4a6155714e1 100644 --- a/arch/x86/boot/bioscall.S +++ b/arch/x86/boot/bioscall.S @@ -32,7 +32,7 @@ intcall: movw %dx, %si movw %sp, %di movw $11, %cx - rep; movsl + rep movsl /* Pop full state from the stack */ popal @@ -67,7 +67,7 @@ intcall: jz 4f movw %sp, %si movw $11, %cx - rep; movsl + rep movsl 4: addw $44, %sp /* Restore state and return */ diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h index 38f17a1e1e367..f3771a6373c76 100644 --- a/arch/x86/boot/boot.h +++ b/arch/x86/boot/boot.h @@ -155,14 +155,14 @@ static inline void wrgs32(u32 v, addr_t addr) static inline bool memcmp_fs(const void *s1, addr_t s2, size_t len) { bool diff; - asm volatile("fs; repe; cmpsb" CC_SET(nz) + asm volatile("fs repe cmpsb" CC_SET(nz) : CC_OUT(nz) (diff), "+D" (s1), "+S" (s2), "+c" (len)); return diff; } static inline bool memcmp_gs(const void *s1, addr_t s2, size_t len) { bool diff; - asm volatile("gs; repe; cmpsb" CC_SET(nz) + asm volatile("gs repe cmpsb" CC_SET(nz) : CC_OUT(nz) (diff), "+D" (s1), "+S" (s2), "+c" (len)); return diff; } diff --git a/arch/x86/boot/compressed/string.c b/arch/x86/boot/compressed/string.c index 81fc1eaa32299..9af19d9614cba 100644 --- a/arch/x86/boot/compressed/string.c +++ b/arch/x86/boot/compressed/string.c @@ -15,9 +15,9 @@ static void *____memcpy(void *dest, const void *src, size_t n) { int d0, d1, d2; asm volatile( - "rep ; movsl\n\t" + "rep movsl\n\t" "movl %4,%%ecx\n\t" - "rep ; movsb\n\t" + "rep movsb" : "=&c" (d0), "=&D" (d1), "=&S" (d2) : "0" (n >> 2), "g" (n & 3), "1" (dest), "2" (src) : "memory"); @@ -29,9 +29,9 @@ static void *____memcpy(void *dest, const void *src, size_t n) { long d0, d1, d2; asm volatile( - "rep ; movsq\n\t" + "rep movsq\n\t" "movq %4,%%rcx\n\t" - "rep ; movsb\n\t" + "rep movsb" : "=&c" (d0), "=&D" (d1), "=&S" (d2) : "0" (n >> 3), "g" (n & 7), "1" (dest), "2" (src) : "memory"); diff --git a/arch/x86/boot/copy.S b/arch/x86/boot/copy.S index 6afd05e819d26..3973a67cd04e4 100644 --- a/arch/x86/boot/copy.S +++ b/arch/x86/boot/copy.S @@ -22,10 +22,10 @@ SYM_FUNC_START_NOALIGN(memcpy) movw %dx, %si pushw %cx shrw $2, %cx - rep; movsl + rep movsl popw %cx andw $3, %cx - rep; movsb + rep movsb popw %di popw %si retl @@ -38,10 +38,10 @@ SYM_FUNC_START_NOALIGN(memset) imull $0x01010101,%eax pushw %cx shrw $2, %cx - rep; stosl + rep stosl popw %cx andw $3, %cx - rep; stosb + rep stosb popw %di retl SYM_FUNC_END(memset) diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S index b5c79f43359bc..9cb91421b4e41 100644 --- a/arch/x86/boot/header.S +++ b/arch/x86/boot/header.S @@ -585,7 +585,7 @@ start_of_setup: xorl %eax, %eax subw %di, %cx shrw $2, %cx - rep; stosl + rep stosl # Jump to C code (should not return) calll main diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c index 84f7a883ce1e8..f35369bb14c51 100644 --- a/arch/x86/boot/string.c +++ b/arch/x86/boot/string.c @@ -32,7 +32,7 @@ int memcmp(const void *s1, const void *s2, size_t len) { bool diff; - asm("repe; cmpsb" CC_SET(nz) + asm("repe cmpsb" CC_SET(nz) : CC_OUT(nz) (diff), "+D" (s1), "+S" (s2), "+c" (len)); return diff; } diff --git a/arch/x86/boot/video.c b/arch/x86/boot/video.c index f2e96905b3fe2..0641c8c46aee2 100644 --- a/arch/x86/boot/video.c +++ b/arch/x86/boot/video.c @@ -292,7 +292,7 @@ static void restore_screen(void) "shrw %%cx ; " "jnc 1f ; " "stosw \n\t" - "1: rep;stosl ; " + "1: rep stosl ; " "popw %%es" : "+D" (dst), "+c" (npad) : "bdS" (video_segment), -- 2.47.2