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Re: [PATCH] [RFC] rs6000: -mreadonly-in-sdata (PR82411)
- From: Segher Boessenkool <segher at kernel dot crashing dot org>
- To: Kees Cook <keescook at google dot com>
- Cc: gcc-patches at gcc dot gnu dot org, David Edelsohn <dje dot gcc at gmail dot com>, Kees Cook <kees at outflux dot net>
- Date: Wed, 28 Feb 2018 18:54:28 -0600
- Subject: Re: [PATCH] [RFC] rs6000: -mreadonly-in-sdata (PR82411)
- Authentication-results: sourceware.org; auth=none
- References: <61d0d76104e9cee5a413ae050772870bcb47d49e.1519768361.git.segher@kernel.crashing.org> <CAGXu5jK7vKFPGNxjspdOYofg0DPRVdFcDpMvXvsRMH=b=XMzCQ@mail.gmail.com> <20180228232334.GE21977@gate.crashing.org> <CAGXu5j+aJLpYmbA+nq+oSaby0neBk9gN=buoZLwreakcJqaOWg@mail.gmail.com> <20180301003919.GF21977@gate.crashing.org> <CAGXu5jLYn_hxov5RX6YY1V+ZKhvh6=WGs7zNm9nfGLcc0iLwsQ@mail.gmail.com>
On Wed, Feb 28, 2018 at 04:43:56PM -0800, Kees Cook wrote:
> On Wed, Feb 28, 2018 at 4:39 PM, Segher Boessenkool
> <segher@kernel.crashing.org> wrote:
> > On Wed, Feb 28, 2018 at 04:15:23PM -0800, Kees Cook wrote:
> >> On Wed, Feb 28, 2018 at 3:23 PM, Segher Boessenkool
> >> <segher@kernel.crashing.org> wrote:
> >> > I'm trying to figure out how to get that file to build at all :-)
> >
> >> $ CROSS_COMPILE=powerpc-linux-gnu- ARCH=powerpc make wii_defconfig
> >> $ for i in CONFIG_STRICT_KERNEL_RWX \
> >> CONFIG_DEBUG_KERNEL \
> >> CONFIG_DEBUG_RODATA_TEST ; do
> >> CROSS_COMPILE=powerpc-linux-gnu- ARCH=powerpc ./scripts/config -e $i
> >> done
> >
> > I use ppc6xx_defconfig normally; I had to disable CONFIG_HIBERNATION
> > as well.
> >
> > Without the new flag, rodata_test_data ends up in .sdata in the object
> > file and in .data in vmlinux.
> >
> > Adding
> >
> > ===
> > diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> > index ccd2556..31b9613 100644
> > --- a/arch/powerpc/Makefile
> > +++ b/arch/powerpc/Makefile
> > @@ -143,6 +143,8 @@ CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mcmodel=med
> > CFLAGS-$(CONFIG_PPC64) += $(call cc-option,-mno-pointers-to-nested-functions)
> > CFLAGS-$(CONFIG_PPC32) := -ffixed-r2 $(MULTIPLEWORD)
> >
> > +CFLAGS-$(CONFIG_PPC32) += $(call cc-option,-mno-readonly-in-sdata)
> > +
> > ifeq ($(CONFIG_PPC_BOOK3S_64),y)
> > CFLAGS-$(CONFIG_GENERIC_CPU) += $(call cc-option,-mtune=power7,-mtune=power4)
> > CFLAGS-$(CONFIG_GENERIC_CPU) += -mcpu=power4
> > ===
> >
> > it ends up in .rodata in both.
>
> Excellent! That's perfect. :)
>
> > It would be nice to have a more comprehensive test, but this will do; I'll
> > commit it tomorrow (will resend, with doc and changelog and all that).
>
> Thank you! Do you want to send the Makefile fix upstream too, or
> should I route that?
If you could? Have my
Signed-off-by: Segher Boessenkool <segher@kernel.crashing.org>
if you want.
It'll be a while before all users have a compiler with the new flag, but
I'll backport it to GCC 7 and GCC 6 (the open release branches) to speed
that up a bit.
Segher