Commit 6aac80a8 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Borislav Petkov
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x86/boot/compressed: Avoid touching ECX in startup32_set_idt_entry() 



Avoid touching register %ecx in startup32_set_idt_entry(), by folding
the MOV, SHL and ORL instructions into a single ORL which no longer
requires a temp register.

This permits ECX to be used as a function argument in a subsequent
patch.

Signed-off-by: default avatarArd Biesheuvel <ardb@kernel.org>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20221122161017.2426828-10-ardb@kernel.org
parent 630f337f

arch/x86/boot/compressed/head_64.S

+2 −6
Original line number Diff line number Diff line
@@ -733,7 +733,6 @@ SYM_DATA_END_LABEL(boot32_idt, SYM_L_GLOBAL, boot32_idt_end) 
 */

SYM_FUNC_START(startup32_set_idt_entry)

	push    %ebx

	push    %ecx



	/* IDT entry address to %ebx */

	leal    rva(boot32_idt)(%ebp), %ebx
@@ -743,9 +742,7 @@ SYM_FUNC_START(startup32_set_idt_entry) 
	/* Build IDT entry, lower 4 bytes */

	movl    %eax, %edx

	andl    $0x0000ffff, %edx		# Target code segment offset [15:0]

	movl    $__KERNEL32_CS, %ecx	# Target code segment selector

	shl     $16, %ecx

	orl     %ecx, %edx

	orl	$(__KERNEL32_CS << 16), %edx	# Target code segment selector



	/* Store lower 4 bytes to IDT */

	movl    %edx, (%ebx)
@@ -758,7 +755,6 @@ SYM_FUNC_START(startup32_set_idt_entry) 
	/* Store upper 4 bytes to IDT */

	movl    %edx, 4(%ebx)



	pop     %ecx

	pop     %ebx

	RET

SYM_FUNC_END(startup32_set_idt_entry)