| Message ID | 1307635142-11312-5-git-send-email-will.deacon@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Jun 09, 2011 at 04:58:56PM +0100, 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 <dave.martin@linaro.org> > Signed-off-by: Will Deacon <will.deacon@arm.com> > --- > 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.S > > diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile > index 59ff42d..5fa67de 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 sha1.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.o > > diff --git a/arch/arm/lib/switch_stack.S b/arch/arm/lib/switch_stack.S > new file mode 100644 > index 0000000..76e3844 > --- /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, #4] Looks like this should be ldr lr, [sp, #4]! ...otherwise we'll also load the lr value into sp. Looks like that may have been my mistake. ---Dave > + ldr sp, [sp] > + mov pc, lr > +ENDPROC(switch_stack) > -- > 1.7.0.4 >
On Thu, Jun 09, 2011 at 05:11:13PM +0100, Dave Martin wrote: > On Thu, Jun 09, 2011 at 04:58:56PM +0100, 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 <dave.martin@linaro.org> > > Signed-off-by: Will Deacon <will.deacon@arm.com> > > --- > > 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.S > > > > diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile > > index 59ff42d..5fa67de 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 sha1.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.o > > > > diff --git a/arch/arm/lib/switch_stack.S b/arch/arm/lib/switch_stack.S > > new file mode 100644 > > index 0000000..76e3844 > > --- /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, #4] > > Looks like this should be > > ldr lr, [sp, #4]! > > ...otherwise we'll also load the lr value into sp. > Looks like that may have been my mistake. Argh I really meant: ldr lr, [sp], #4 Apologies for the confusion! Cheers ---Dave
diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile index 59ff42d..5fa67de 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 sha1.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.o diff --git a/arch/arm/lib/switch_stack.S b/arch/arm/lib/switch_stack.S new file mode 100644 index 0000000..76e3844 --- /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, #4] + ldr sp, [sp] + mov pc, lr +ENDPROC(switch_stack)