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Commit 36d3793c authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

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: default avatarH. Peter Anvin <hpa@zytor.com>
parent 97541912

arch/x86/boot/compressed/head_32.S

+6 −5
Original line number Diff line number Diff line
@@ -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..

arch/x86/boot/compressed/head_64.S

+13 −13
Original line number Diff line number Diff line
@@ -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..