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x86/boot: Remove semicolon from "rep" prefixes

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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 <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
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: Martin Mares <mj@ucw.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250418071437.4144391-1-ubizjak@gmail.com
This commit is contained in:
Uros Bizjak 2025-04-18 09:13:50 +02:00 • committed by Ingo Molnar
parent 498cb872a1
commit 0dcc51477b
7 changed files with 15 additions and 15 deletions
Download patch file Download diff file Expand all files Collapse all files

4
arch/x86/boot/bioscall.S
View file

@ -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 */

4
arch/x86/boot/boot.h
View file

@ -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;
}

8
arch/x86/boot/compressed/string.c
View file

@ -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");

8
arch/x86/boot/copy.S
View file

@ -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)

2
arch/x86/boot/header.S
View file

@ -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

2
arch/x86/boot/string.c
View file

@ -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;
}

2
arch/x86/boot/video.c
View file

@ -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),