Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753907AbcD1Uvw (ORCPT ); Thu, 28 Apr 2016 16:51:52 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53307 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753405AbcD1UpN (ORCPT ); Thu, 28 Apr 2016 16:45:13 -0400 From: Josh Poimboeuf To: Jessica Yu , Jiri Kosina , Miroslav Benes , Ingo Molnar , Peter Zijlstra , Michael Ellerman , Heiko Carstens Cc: live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, Vojtech Pavlik , Jiri Slaby , Petr Mladek , Chris J Arges , Andy Lutomirski Subject: [RFC PATCH v2 03/18] x86/asm/head: standardize the bottom of the stack for idle tasks Date: Thu, 28 Apr 2016 15:44:34 -0500 Message-Id: <9268772b31cc7bc4dc40c617e3baf45e07322145.1461875890.git.jpoimboe@redhat.com> In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1736 Lines: 50 Thanks to all the recent x86 entry code refactoring, most tasks' kernel stacks start at the same offset right above their saved pt_regs, regardless of which syscall was used to enter the kernel. That creates a nice convention which makes it straightforward to identify the "bottom" of the stack, which can be useful for stack walking code which needs to verify the stack is sane. However there are still a few types of tasks which don't yet follow that convention: 1) CPU idle tasks, aka the "swapper" tasks 2) freshly forked TIF_FORK tasks which don't have a stack at all Make the idle tasks conform to the new stack bottom convention by starting their stack at a sizeof(pt_regs) offset from the end of the stack page. Signed-off-by: Josh Poimboeuf --- arch/x86/kernel/head_64.S | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index 6dbd2c0..0b12311 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -296,8 +296,9 @@ ENTRY(start_cpu) * REX.W + FF /5 JMP m16:64 Jump far, absolute indirect, * address given in m16:64. */ - movq initial_code(%rip),%rax - pushq $0 # fake return address to stop unwinder + call 1f # put return address on stack for unwinder +1: xorq %rbp, %rbp # clear frame pointer + movq initial_code(%rip), %rax pushq $__KERNEL_CS # set correct cs pushq %rax # target address in negative space lretq @@ -325,7 +326,7 @@ ENDPROC(start_cpu0) GLOBAL(initial_gs) .quad INIT_PER_CPU_VAR(irq_stack_union) GLOBAL(initial_stack) - .quad init_thread_union+THREAD_SIZE-8 + .quad init_thread_union + THREAD_SIZE - SIZEOF_PTREGS __FINITDATA bad_address: -- 2.4.11