linux-kernel - [RFC PATCH 8/9] x86/purgatory: Simplify references to regs array

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Date: Wed, 24 Apr 2024 17:53:18 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org, Ard Biesheuvel <ardb@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
	Eric Biederman <ebiederm@...ssion.com>, kexec@...ts.infradead.org, 
	Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, 
	Kees Cook <keescook@...omium.org>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, Masahiro Yamada <masahiroy@...nel.org>
Subject: [RFC PATCH 8/9] x86/purgatory: Simplify references to regs array

From: Ard Biesheuvel <ardb@...nel.org>

Use a single symbol reference and offset addressing to load the contents
of the register file from memory, instead of using a symbol reference
for each, which results in larger code and more ELF overhead. While at
it, rename the individual labels with an .L prefix so they are omitted
from the ELF symbol table.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/x86/purgatory/entry64.S | 67 ++++++++++----------
 1 file changed, 34 insertions(+), 33 deletions(-)

diff --git a/arch/x86/purgatory/entry64.S b/arch/x86/purgatory/entry64.S
index 3d09781d4f9a..56487fb7fa1d 100644
--- a/arch/x86/purgatory/entry64.S
+++ b/arch/x86/purgatory/entry64.S
@@ -37,45 +37,46 @@ SYM_CODE_START(entry64)
 new_cs_exit:
 
 	/* Load the registers */
-	movq	rax(%rip), %rax
-	movq	rbx(%rip), %rbx
-	movq	rcx(%rip), %rcx
-	movq	rdx(%rip), %rdx
-	movq	rsi(%rip), %rsi
-	movq	rdi(%rip), %rdi
-	movq	rbp(%rip), %rbp
-	movq	r8(%rip), %r8
-	movq	r9(%rip), %r9
-	movq	r10(%rip), %r10
-	movq	r11(%rip), %r11
-	movq	r12(%rip), %r12
-	movq	r13(%rip), %r13
-	movq	r14(%rip), %r14
-	movq	r15(%rip), %r15
+	leaq	entry64_regs(%rip), %r15
+	movq	0x00(%r15), %rax
+	movq	0x08(%r15), %rcx
+	movq	0x10(%r15), %rdx
+	movq	0x18(%r15), %rbx
+	movq	0x20(%r15), %rbp
+	movq	0x28(%r15), %rsi
+	movq	0x30(%r15), %rdi
+	movq	0x38(%r15), %r8
+	movq	0x40(%r15), %r9
+	movq	0x48(%r15), %r10
+	movq	0x50(%r15), %r11
+	movq	0x58(%r15), %r12
+	movq	0x60(%r15), %r13
+	movq	0x68(%r15), %r14
+	movq	0x70(%r15), %r15
 
 	/* Jump to the new code... */
-	jmpq	*rip(%rip)
+	jmpq	*.Lrip(%rip)
 SYM_CODE_END(entry64)
 
 	.section ".rodata"
-	.balign 4
+	.balign	8
 SYM_DATA_START(entry64_regs)
-rax:	.quad 0x0
-rcx:	.quad 0x0
-rdx:	.quad 0x0
-rbx:	.quad 0x0
-rbp:	.quad 0x0
-rsi:	.quad 0x0
-rdi:	.quad 0x0
-r8:	.quad 0x0
-r9:	.quad 0x0
-r10:	.quad 0x0
-r11:	.quad 0x0
-r12:	.quad 0x0
-r13:	.quad 0x0
-r14:	.quad 0x0
-r15:	.quad 0x0
-rip:	.quad 0x0
+.Lrax:	.quad	0x0
+.Lrcx:	.quad	0x0
+.Lrdx:	.quad	0x0
+.Lrbx:	.quad	0x0
+.Lrbp:	.quad	0x0
+.Lrsi:	.quad	0x0
+.Lrdi:	.quad	0x0
+.Lr8:	.quad	0x0
+.Lr9:	.quad	0x0
+.Lr10:	.quad	0x0
+.Lr11:	.quad	0x0
+.Lr12:	.quad	0x0
+.Lr13:	.quad	0x0
+.Lr14:	.quad	0x0
+.Lr15:	.quad	0x0
+.Lrip:	.quad	0x0
 SYM_DATA_END(entry64_regs)
 
 	/* GDT */
-- 
2.44.0.769.g3c40516874-goog