[PATCH v2] x86/boot/64: Use TEST %reg,%reg instead of CMP $0,%reg

From: Uros Bizjak
Date: Thu Oct 29 2020 - 12:03:12 EST


Use TEST %reg,%reg which sets the zero flag in the same way
as CMP $0,%reg, but the encoding uses one byte less.

v2: Correct commit subject

Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Reviewed-by: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
---
arch/x86/boot/compressed/head_64.S | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 017de6cc87dc..e94874f4bbc1 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -241,12 +241,12 @@ SYM_FUNC_START(startup_32)
leal rva(startup_64)(%ebp), %eax
#ifdef CONFIG_EFI_MIXED
movl rva(efi32_boot_args)(%ebp), %edi
- cmp $0, %edi
+ testl %edi, %edi
jz 1f
leal rva(efi64_stub_entry)(%ebp), %eax
movl rva(efi32_boot_args+4)(%ebp), %esi
movl rva(efi32_boot_args+8)(%ebp), %edx // saved bootparams pointer
- cmpl $0, %edx
+ testl %edx, %edx
jnz 1f
/*
* efi_pe_entry uses MS calling convention, which requires 32 bytes of
@@ -592,7 +592,7 @@ SYM_CODE_START(trampoline_32bit_src)
movl %eax, %cr0

/* Check what paging mode we want to be in after the trampoline */
- cmpl $0, %edx
+ testl %edx, %edx
jz 1f

/* We want 5-level paging: don't touch CR3 if it already points to 5-level page tables */
@@ -622,7 +622,7 @@ SYM_CODE_START(trampoline_32bit_src)

/* Enable PAE and LA57 (if required) paging modes */
movl $X86_CR4_PAE, %eax
- cmpl $0, %edx
+ testl %edx, %edx
jz 1f
orl $X86_CR4_LA57, %eax
1:
--
2.26.2