Commit 2d81f1fe authored by Will Deacon's avatar Will Deacon
Browse files

ARM: lib: add call_with_stack function for safely changing stack

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, call_with_stack:

	void call_with_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.
Reviewed-by: default avatarNicolas Pitre <>
Reviewed-by: default avatarCatalin Marinas <>
Signed-off-by: default avatarDave Martin <>
Signed-off-by: default avatarWill Deacon <>
parent ad622671
......@@ -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 \
mmu-y := clear_user.o copy_page.o getuser.o putuser.o
* arch/arm/lib/call_with_stack.S
* Copyright (C) 2011 ARM Ltd.
* Written by Will Deacon <>
* 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
* 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 call_with_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.
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
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