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Message-Id: <20221122161017.2426828-10-ardb@kernel.org>
Date: Tue, 22 Nov 2022 17:10:09 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: linux-efi@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Michael Roth <michael.roth@....com>
Subject: [PATCH v3 09/17] x86/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: Ard Biesheuvel <ardb@...nel.org>
---
arch/x86/boot/compressed/head_64.S | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)
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)
--
2.35.1
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