linux-kernel - [RFC 06/17] x86/asm/64: Use pop instead of movq in syscall_return_via

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Date:   Wed,  6 Sep 2017 14:36:51 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: [RFC 06/17] x86/asm/64: Use pop instead of movq in syscall_return_via_sysret

Saves 64 bytes.

Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/entry/entry_64.S | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 741b7dc1758b..45d4cb8fd81b 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -308,9 +308,17 @@ return_from_SYSCALL_64:
 	 */
 syscall_return_via_sysret:
 	/* rcx and r11 are already restored (see code above) */
-	RESTORE_EXTRA_REGS
-	RESTORE_C_REGS_EXCEPT_RCX_R11
-	movq	RSP(%rsp), %rsp
+	POP_EXTRA_REGS
+	popq	%rsi	/* skip r11 */
+	popq	%r10
+	popq	%r9
+	popq	%r8
+	popq	%rax
+	popq	%rsi	/* skip rcx */
+	popq	%rdx
+	popq	%rsi
+	popq	%rdi
+	movq	RSP-ORIG_RAX(%rsp), %rsp
 	USERGS_SYSRET64
 END(entry_SYSCALL_64)
 
-- 
2.13.5