[PATCH v4 3/8] ARM: lib: add switch_stack function for safely changing stack
From: Nicolas Pitre <hidden>
Date: 2011-08-24 01:07:29
On Tue, 23 Aug 2011, Will Deacon wrote:
When disabling the MMU, it is necessary to take out a 1:1 identity map of the reset code so that it can safely be executed with and without the MMU active. To avoid the situation where the physical address of the reset code aliases with the virtual address of the active stack (which cannot be included in the 1:1 mapping), it is desirable to change to a new stack at a location which is less likely to alias. This code adds a new lib function, switch_stack: void switch_stack(void (*fn)(void *), void *arg, void *sp); which changes the stack to point at the sp parameter, before invoking fn(arg) with the new stack selected. Signed-off-by: Dave Martin <redacted> Signed-off-by: Will Deacon <redacted>
For the implementation: Reviewed-by: Nicolas Pitre <redacted> However I think switch_stack() is too vague a name for what this actually does. Maybe something like call_with_stack(fn, arg, sp) is more precise.
quoted hunk ↗ jump to hunk
--- arch/arm/lib/Makefile | 3 +- arch/arm/lib/switch_stack.S | 44 +++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 46 insertions(+), 1 deletions(-) create mode 100644 arch/arm/lib/switch_stack.Sdiff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile index cf73a7f..cbb1bc1 100644 --- a/arch/arm/lib/Makefile +++ b/arch/arm/lib/Makefile@@ -13,7 +13,8 @@ lib-y := backtrace.o changebit.o csumipv6.o csumpartial.o \ testchangebit.o testclearbit.o testsetbit.o \ ashldi3.o ashrdi3.o lshrdi3.o muldi3.o \ ucmpdi2.o lib1funcs.o div64.o \ - io-readsb.o io-writesb.o io-readsl.o io-writesl.o + io-readsb.o io-writesb.o io-readsl.o io-writesl.o \ + switch_stack.o mmu-y := clear_user.o copy_page.o getuser.o putuser.odiff --git a/arch/arm/lib/switch_stack.S b/arch/arm/lib/switch_stack.S new file mode 100644 index 0000000..552090d --- /dev/null +++ b/arch/arm/lib/switch_stack.S@@ -0,0 +1,44 @@ +/* + * arch/arm/lib/switch_stack.S + * + * Copyright (C) 2011 ARM Ltd. + * Written by Will Deacon <will.deacon@arm.com> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License version 2 as + * published by the Free Software Foundation. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + */ + +#include <linux/linkage.h> +#include <asm/assembler.h> + +/* + * void switch_stack(void (*fn)(void *), void *arg, void *sp) + * + * Change the stack to that pointed at by sp, then invoke fn(arg) with + * the new stack. + */ +ENTRY(switch_stack) + str sp, [r2, #-4]! + str lr, [r2, #-4]! + + mov sp, r2 + mov r2, r0 + mov r0, r1 + + adr lr, BSYM(1f) + mov pc, r2 + +1: ldr lr, [sp] + ldr sp, [sp, #4] + mov pc, lr +ENDPROC(switch_stack)-- 1.7.0.4 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel at lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel