linux-efi.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Arvind Sankar <nivedita@alum.mit.edu>
To: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Ard Biesheuvel <ardb@kernel.org>
Cc: linux-efi@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH v2 7/7] x86/boot: Micro-optimize GDT loading instructions
Date: Sun,  2 Feb 2020 12:13:53 -0500	[thread overview]
Message-ID: <20200202171353.3736319-8-nivedita@alum.mit.edu> (raw)
In-Reply-To: <20200202171353.3736319-1-nivedita@alum.mit.edu>

Rearrange the instructions a bit to use a 32-bit displacement once
instead of 2/3 times. This saves 8 bytes of machine code.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
---
 arch/x86/boot/compressed/head_64.S | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index c36e6156b6a3..a4f5561c1c0e 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -69,8 +69,9 @@ SYM_FUNC_START(startup_32)
 	subl	$1b, %ebp
 
 	/* Load new GDT with the 64bit segments using 32bit descriptor */
-	addl	%ebp, gdt+2(%ebp)
-	lgdt	gdt(%ebp)
+	leal	gdt(%ebp), %eax
+	movl	%eax, 2(%eax)
+	lgdt	(%eax)
 
 	/* Load segment registers with our descriptors */
 	movl	$__BOOT_DS, %eax
@@ -355,9 +356,9 @@ SYM_CODE_START(startup_64)
 	 */
 
 	/* Make sure we have GDT with 32-bit code segment */
-	leaq	gdt(%rip), %rax
-	movq	%rax, gdt64+2(%rip)
-	lgdt	gdt64(%rip)
+	leaq	gdt64(%rip), %rax
+	addq	%rax, 2(%rax)
+	lgdt	(%rax)
 
 	/*
 	 * paging_prepare() sets up the trampoline and checks if we need to
@@ -625,12 +626,12 @@ SYM_FUNC_END(.Lno_longmode)
 	.data
 SYM_DATA_START_LOCAL(gdt64)
 	.word	gdt_end - gdt - 1
-	.quad   0
+	.quad   gdt - gdt64
 SYM_DATA_END(gdt64)
 	.balign	8
 SYM_DATA_START_LOCAL(gdt)
 	.word	gdt_end - gdt - 1
-	.long	gdt
+	.long	0
 	.word	0
 	.quad	0x00cf9a000000ffff	/* __KERNEL32_CS */
 	.quad	0x00af9a000000ffff	/* __KERNEL_CS */
-- 
2.24.1


  parent reply	other threads:[~2020-02-02 17:14 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-30 20:04 [PATCH 0/8] Remove 64-bit GDT setup in efi_main + doc fixes Arvind Sankar
2020-01-30 20:04 ` [PATCH 1/8] efi/x86: Use C wrapper instead of inline assembly Arvind Sankar
2020-01-30 20:04 ` [PATCH 2/8] efi/x86: Allocate the GDT pointer on the stack Arvind Sankar
2020-01-30 20:04 ` [PATCH 3/8] efi/x86: Factor GDT setup code into a function Arvind Sankar
2020-01-30 20:04 ` [PATCH 4/8] efi/x86: Only setup the GDT for 32-bit kernel Arvind Sankar
2020-01-30 20:04 ` [PATCH 5/8] efi/x86: Allocate only the required 32 bytes for the GDT Arvind Sankar
2020-01-30 20:04 ` [PATCH 6/8] efi/x86: Change __KERNEL_{CS,DS} to __BOOT_{CS,DS} Arvind Sankar
2020-01-30 20:04 ` [PATCH 7/8] Documentation/x86/boot: Clarify segment requirements for EFI handover Arvind Sankar
2020-01-31 19:24   ` Arvind Sankar
2020-01-30 20:04 ` [PATCH 8/8] Documentation/x86/boot: Correct segment requirements for 64-bit boot Arvind Sankar
2020-01-31  8:42 ` [PATCH 0/8] Remove 64-bit GDT setup in efi_main + doc fixes Ard Biesheuvel
2020-01-31  9:31   ` Ard Biesheuvel
2020-01-31 19:10     ` Arvind Sankar
2020-02-02 17:13 ` [PATCH v2 0/7] x86/efi,boot: GDT handling cleanup/fixes Arvind Sankar
2020-02-02 17:13   ` [PATCH v2 1/7] x86/boot: Remove KEEP_SEGMENTS support Arvind Sankar
2020-02-02 17:13   ` [PATCH v2 2/7] efi/x86: Don't depend on firmware GDT layout Arvind Sankar
2020-02-02 17:54     ` Ard Biesheuvel
2020-02-02 18:18       ` Arvind Sankar
2020-02-02 17:13   ` [PATCH v2 3/7] x86/boot: Reload GDTR after copying to the end of the buffer Arvind Sankar
2020-02-02 17:13   ` [PATCH v2 4/7] x86/boot: Clear direction and interrupt flags in startup_64 Arvind Sankar
2020-02-02 17:13   ` [PATCH v2 5/7] efi/x86: Remove GDT setup from efi_main Arvind Sankar
2020-02-02 17:13   ` [PATCH v2 6/7] x86/boot: GDT limit value should be size - 1 Arvind Sankar
2020-02-02 17:13   ` Arvind Sankar [this message]
2020-02-02 18:01   ` [PATCH v2 0/7] x86/efi,boot: GDT handling cleanup/fixes Ard Biesheuvel

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200202171353.3736319-8-nivedita@alum.mit.edu \
    --to=nivedita@alum.mit.edu \
    --cc=ardb@kernel.org \
    --cc=bp@alien8.de \
    --cc=hpa@zytor.com \
    --cc=linux-efi@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=tglx@linutronix.de \
    --cc=x86@kernel.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).