linux-kernel - [PATCH 1/2] x86_32, asm: Improve a TOP_OF_KERNEL_STACK

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Message-Id: <41fee7bb8490ae840fe7ef2699f9c2feb932e729.1428002830.git.luto@kernel.org>
Date:	Thu,  2 Apr 2015 12:41:44 -0700
From:	Andy Lutomirski <luto@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>, X86 ML <x86@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...capital.net>
Subject: [PATCH 1/2] x86_32, asm: Improve a TOP_OF_KERNEL_STACK_PADDING comment and long asm line

From: Andy Lutomirski <luto@...capital.net>

At Denys' request, clean up the comment describing stack padding in
the 32-bit sysenter path.  This also fixes a long line of asm.  No
code changes.

Signed-off-by: Andy Lutomirski <luto@...capital.net>
---
 arch/x86/kernel/entry_32.S | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S
index 4c8cc34e6d68..438d19389f67 100644
--- a/arch/x86/kernel/entry_32.S
+++ b/arch/x86/kernel/entry_32.S
@@ -395,10 +395,14 @@ sysenter_past_esp:
 	/*CFI_REL_OFFSET cs, 0*/
 	/*
 	 * Push current_thread_info()->sysenter_return to the stack.
-	 * A tiny bit of offset fixup is necessary - 4*4 means the 4 words
-	 * pushed above; +8 corresponds to copy_thread's esp0 setting.
+	 * A tiny bit of offset fixup is necessary: TI_sysenter_return
+	 * is relative to thread_info, which is at the bottom of the
+	 * kernel stack page.  4*4 means the 4 words pushed above;
+	 * TOP_OF_KERNEL_STACK_PADDING takes us to the top of the stack;
+	 * and THREAD_SIZE takes us to the bottom.
 	 */
-	pushl_cfi ((TI_sysenter_return)-THREAD_SIZE+TOP_OF_KERNEL_STACK_PADDING+4*4)(%esp)
+	pushl_cfi ((TI_sysenter_return) - THREAD_SIZE + \
+	           TOP_OF_KERNEL_STACK_PADDING + 4*4)(%esp)
 	CFI_REL_OFFSET eip, 0
 
 	pushl_cfi %eax
-- 
2.3.0

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