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minor optimization in our assembler code

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This commit is contained in:
Stefan Lankes 2011-03-08 14:39:21 +01:00
parent d201c4d1bc
commit ed29ee444a
2 changed files with 16 additions and 20 deletions
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8
arch/x86/include/asm/string.h
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@ -32,10 +32,10 @@ inline static void *memcpy(void* dest, const void *src, size_t count)
return dest;
asm volatile (
"cld; rep ; movsl\n\t"
"cld; rep movsl\n\t"
"movl %4, %%ecx\n\t"
"andl $3, %%ecx\n\t"
"rep ; movsb\n\t"
"rep movsb\n\t"
: "=&c"(i), "=&D"(j), "=&S"(k)
: "0"(count/4), "g"(count), "1"(dest), "2"(src) : "memory");
@ -51,7 +51,7 @@ inline static void *memset(void* dest, int val, size_t count)
if (BUILTIN_EXPECT(!dest, 0))
return dest;
asm volatile ("cld; rep ; stosb"
asm volatile ("cld; rep stosb"
: "=&c"(i), "=&D"(j)
: "a"(val), "1"(dest), "0"(count) : "memory");
@ -68,7 +68,7 @@ inline static size_t strlen(const char* str)
if (BUILTIN_EXPECT(!str, 0))
return len;
asm volatile("not %%ecx; cld; repne ; scasb; not %%ecx; dec %%ecx"
asm volatile("not %%ecx; cld; repne scasb; not %%ecx; dec %%ecx"
: "=&c"(len), "=&D"(i), "=&a"(j)
: "2"(0), "1"(str), "0"(len)
: "memory");

28
arch/x86/kernel/string.asm
View file

@ -60,39 +60,35 @@ L3:
pop ebp
ret
; The following function based on JamesM's kernel development tutorials
; The following function is derived from JamesM's kernel development tutorials
; (http://www.jamesmolloy.co.uk/tutorial_html/)
global copy_page_physical
copy_page_physical:
push ebx ; According to __cdecl, we must preserve the contents of EBX.
push esi ; According to __cdecl, we must preserve the contents of ESI
push edi ; and EDI.
pushf ; push EFLAGS, so we can pop it and reenable interrupts
; later, if they were enabled anyway.
cli ; Disable interrupts, so we aren't interrupted.
; Load these in BEFORE we disable paging!
mov ebx, [esp+16] ; Source address
mov ecx, [esp+12] ; Destination address
mov edi, [esp+12+4] ; Destination address
mov esi, [esp+12+8] ; Source address
mov edx, cr0 ; Get the control register...
and edx, 0x7fffffff ; and...
mov cr0, edx ; Disable paging.
mov edx, 1024 ; 1024*4bytes = 4096 bytes
L4:
mov eax, [ebx] ; Get the word at the source address
mov [ecx], eax ; Store it at the dest address
add ebx, 4 ; Source address += sizeof(word)
add ecx, 4 ; Dest address += sizeof(word)
dec edx ; One less word to do
jnz L4
cld
mov ecx, 0x400 ; 1024*4bytes = 4096 bytes = page size
rep movsd ; copy page
mov edx, cr0 ; Get the control register again
or edx, 0x80000000 ; and...
mov cr0, edx ; Enable paging.
popf ; Pop EFLAGS back.
pop ebx ; Get the original value of EBX back.
pop edi ; Get the original value of EDI
pop esi ; and ESI back.
ret
SECTION .note.GNU-stack noalloc noexec nowrite progbits