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x86, boot: use appropriate rep string for move and clear 

In the pre-decompression code, use the appropriate largest possible
rep movs and rep stos to move code and clear bss, respectively.  For
reverse copy, do note that the initial values are supposed to be the
address of the first (highest) copy datum, not one byte beyond the end
of the buffer.

rep strings are not necessarily the fastest way to perform these
operations on all current processors, but are likely to be in the
future, and perhaps more importantly, we want to encourage the
architecturally right thing to do here.

This also fixes a couple of trivial inefficiencies on 64 bits.

[ Impact: trivial performance enhancement, increase code similarity ]

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
H. Peter Anvin 2009-05-08 16:45:15 -07:00
parent 9754191278
commit 36d3793c94
2 changed files with 19 additions and 18 deletions
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11
arch/x86/boot/compressed/head_32.S
View File

@ -100,11 +100,12 @@ ENTRY(startup_32)
* where decompression in place becomes safe.
*/
pushl %esi
leal _bss(%ebp), %esi
leal _bss(%ebx), %edi
leal (_bss-4)(%ebp), %esi
leal (_bss-4)(%ebx), %edi
movl $(_bss - startup_32), %ecx
shrl $2, %ecx
std
rep movsb
rep movsl
cld
popl %esi
@ -135,8 +136,8 @@ relocated:
leal _bss(%ebx), %edi
leal _ebss(%ebx), %ecx
subl %edi, %ecx
cld
rep stosb
shrl $2, %ecx
rep stosl
/*
* Do the decompression, and jump to the new kernel..

26
arch/x86/boot/compressed/head_64.S
View File

@ -260,15 +260,15 @@ ENTRY(startup_64)
* Copy the compressed kernel to the end of our buffer
* where decompression in place becomes safe.
*/
leaq _bss(%rip), %r8
leaq _bss(%rbx), %r9
pushq %rsi
leaq (_bss-8)(%rip), %rsi
leaq (_bss-8)(%rbx), %rdi
movq $_bss /* - $startup_32 */, %rcx
1: subq $8, %r8
subq $8, %r9
movq 0(%r8), %rax
movq %rax, 0(%r9)
subq $8, %rcx
jnz 1b
shrq $3, %rcx
std
rep movsq
cld
popq %rsi
/*
* Jump to the relocated address.
@ -282,12 +282,12 @@ relocated:
/*
* Clear BSS (stack is currently empty)
*/
xorq %rax, %rax
leaq _bss(%rbx), %rdi
leaq _ebss(%rbx), %rcx
xorl %eax, %eax
leaq _bss(%rip), %rdi
leaq _ebss(%rip), %rcx
subq %rdi, %rcx
cld
rep stosb
shrq $3, %rcx
rep stosq
/*
* Do the decompression, and jump to the new kernel..