diff mbox series

[v3,09/17] x86/compressed: avoid touching ECX in startup32_set_idt_entry()

Message ID 20221122161017.2426828-10-ardb@kernel.org
State Accepted
Commit 6aac80a8da46d70f2ae7ff97c9f45a15c7c9b3ef
Headers show
Series [v3,01/17] x86/compressed: efi-mixed: rename efi_thunk_64.S to efi-mixed.S | expand

Commit Message

Ard Biesheuvel Nov. 22, 2022, 4:10 p.m. UTC 
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: Ard Biesheuvel <ardb@kernel.org>
---
 arch/x86/boot/compressed/head_64.S | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)
diff mbox series

Patch

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 66ad3ab802ca9d0c..f31277f455e63f5f 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -741,7 +741,6 @@  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
@@ -750,10 +749,8 @@  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
+	andl    $0x0000ffff, %edx		# Target code segment offset [15:0]
+	orl	$(__KERNEL32_CS << 16), %edx	# Target code segment selector
 
 	/* Store lower 4 bytes to IDT */
 	movl    %edx, (%ebx)
@@ -766,7 +763,6 @@  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)