* [PATCH] x86: prevent gcc from emitting SSE into boot code
@ 2016-06-22 17:37 Dmitry Vyukov
2016-06-22 20:17 ` Dmitry Vyukov
0 siblings, 1 reply; 4+ messages in thread
From: Dmitry Vyukov @ 2016-06-22 17:37 UTC (permalink / raw)
To: hpa, tglx, mingo, x86
Cc: linux-kernel, glider, ryabinin.a.a, kasan-dev, Dmitry Vyukov
Latest gcc manages to emit MOVDQA into boot code
which leads to crashes. Add more -mno-see flags.
Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
---
arch/x86/boot/compressed/Makefile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index f135688..7eaafb8 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -31,7 +31,7 @@ KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
cflags-$(CONFIG_X86_32) := -march=i386
cflags-$(CONFIG_X86_64) := -mcmodel=small
KBUILD_CFLAGS += $(cflags-y)
-KBUILD_CFLAGS += -mno-mmx -mno-sse
+KBUILD_CFLAGS += -mno-mmx -mno-sse -mno-sse2 -mno-sse3
KBUILD_CFLAGS += $(call cc-option,-ffreestanding)
KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
--
2.8.0.rc3.226.g39d4020
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] x86: prevent gcc from emitting SSE into boot code
2016-06-22 17:37 [PATCH] x86: prevent gcc from emitting SSE into boot code Dmitry Vyukov
@ 2016-06-22 20:17 ` Dmitry Vyukov
2016-06-27 18:53 ` Ingo Molnar
0 siblings, 1 reply; 4+ messages in thread
From: Dmitry Vyukov @ 2016-06-22 20:17 UTC (permalink / raw)
To: H. Peter Anvin, Thomas Gleixner, Ingo Molnar, x86
Cc: LKML, Alexander Potapenko, Andrey Ryabinin, kasan-dev, Dmitry Vyukov
On Wed, Jun 22, 2016 at 7:37 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
> Latest gcc manages to emit MOVDQA into boot code
> which leads to crashes. Add more -mno-see flags.
>
> Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
> ---
> arch/x86/boot/compressed/Makefile | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> index f135688..7eaafb8 100644
> --- a/arch/x86/boot/compressed/Makefile
> +++ b/arch/x86/boot/compressed/Makefile
> @@ -31,7 +31,7 @@ KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
> cflags-$(CONFIG_X86_32) := -march=i386
> cflags-$(CONFIG_X86_64) := -mcmodel=small
> KBUILD_CFLAGS += $(cflags-y)
> -KBUILD_CFLAGS += -mno-mmx -mno-sse
> +KBUILD_CFLAGS += -mno-mmx -mno-sse -mno-sse2 -mno-sse3
> KBUILD_CFLAGS += $(call cc-option,-ffreestanding)
> KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
>
> --
> 2.8.0.rc3.226.g39d4020
I withdraw this patch.
>From off-list discussion:
"-mno-sse alone should disable all SSE/AVX instructions. If not,
please file a GCC bug report".
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] x86: prevent gcc from emitting SSE into boot code
2016-06-22 20:17 ` Dmitry Vyukov
@ 2016-06-27 18:53 ` Ingo Molnar
2016-06-27 18:58 ` Dmitry Vyukov
0 siblings, 1 reply; 4+ messages in thread
From: Ingo Molnar @ 2016-06-27 18:53 UTC (permalink / raw)
To: Dmitry Vyukov
Cc: H. Peter Anvin, Thomas Gleixner, Ingo Molnar, x86, LKML,
Alexander Potapenko, Andrey Ryabinin, kasan-dev
* Dmitry Vyukov <dvyukov@google.com> wrote:
> On Wed, Jun 22, 2016 at 7:37 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
> > Latest gcc manages to emit MOVDQA into boot code
> > which leads to crashes. Add more -mno-see flags.
Which GCC version is that?
> >
> > Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
> > ---
> > arch/x86/boot/compressed/Makefile | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> > index f135688..7eaafb8 100644
> > --- a/arch/x86/boot/compressed/Makefile
> > +++ b/arch/x86/boot/compressed/Makefile
> > @@ -31,7 +31,7 @@ KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
> > cflags-$(CONFIG_X86_32) := -march=i386
> > cflags-$(CONFIG_X86_64) := -mcmodel=small
> > KBUILD_CFLAGS += $(cflags-y)
> > -KBUILD_CFLAGS += -mno-mmx -mno-sse
> > +KBUILD_CFLAGS += -mno-mmx -mno-sse -mno-sse2 -mno-sse3
> > KBUILD_CFLAGS += $(call cc-option,-ffreestanding)
> > KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
> >
> > --
> > 2.8.0.rc3.226.g39d4020
>
>
> I withdraw this patch.
>
> From off-list discussion:
>
> "-mno-sse alone should disable all SSE/AVX instructions. If not,
> please file a GCC bug report".
So the GCC documentation says:
-mmmx
-mno-mmx
-msse
-mno-sse
-msse2
-mno-sse2
-msse3
-mno-sse3
-m3dnow
-mno-3dnow
These switches enable or disable the use of built-in functions that allow
direct access to the MMX, SSE, SSE2, SSE3 and 3Dnow extensions of the
instruction set.
Technically -mno-mmx won't turn off SSE instructions because they are independent.
Do we really want to rely on an undocumented property of -mno-sse (clearly broken
in at least one released GCC version), especially as the fix is so easy?
Thanks,
Ingo
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] x86: prevent gcc from emitting SSE into boot code
2016-06-27 18:53 ` Ingo Molnar
@ 2016-06-27 18:58 ` Dmitry Vyukov
0 siblings, 0 replies; 4+ messages in thread
From: Dmitry Vyukov @ 2016-06-27 18:58 UTC (permalink / raw)
To: Ingo Molnar
Cc: H. Peter Anvin, Thomas Gleixner, Ingo Molnar, x86, LKML,
Alexander Potapenko, Andrey Ryabinin, kasan-dev, H.J. Lu
On Mon, Jun 27, 2016 at 8:53 PM, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Dmitry Vyukov <dvyukov@google.com> wrote:
>
>> On Wed, Jun 22, 2016 at 7:37 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
>> > Latest gcc manages to emit MOVDQA into boot code
>> > which leads to crashes. Add more -mno-see flags.
>
> Which GCC version is that?
>
>> >
>> > Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
>> > ---
>> > arch/x86/boot/compressed/Makefile | 2 +-
>> > 1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
>> > index f135688..7eaafb8 100644
>> > --- a/arch/x86/boot/compressed/Makefile
>> > +++ b/arch/x86/boot/compressed/Makefile
>> > @@ -31,7 +31,7 @@ KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
>> > cflags-$(CONFIG_X86_32) := -march=i386
>> > cflags-$(CONFIG_X86_64) := -mcmodel=small
>> > KBUILD_CFLAGS += $(cflags-y)
>> > -KBUILD_CFLAGS += -mno-mmx -mno-sse
>> > +KBUILD_CFLAGS += -mno-mmx -mno-sse -mno-sse2 -mno-sse3
>> > KBUILD_CFLAGS += $(call cc-option,-ffreestanding)
>> > KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
>> >
>> > --
>> > 2.8.0.rc3.226.g39d4020
>>
>>
>> I withdraw this patch.
>>
>> From off-list discussion:
>>
>> "-mno-sse alone should disable all SSE/AVX instructions. If not,
>> please file a GCC bug report".
>
> So the GCC documentation says:
>
> -mmmx
> -mno-mmx
> -msse
> -mno-sse
> -msse2
> -mno-sse2
> -msse3
> -mno-sse3
> -m3dnow
> -mno-3dnow
> These switches enable or disable the use of built-in functions that allow
> direct access to the MMX, SSE, SSE2, SSE3 and 3Dnow extensions of the
> instruction set.
>
> Technically -mno-mmx won't turn off SSE instructions because they are independent.
> Do we really want to rely on an undocumented property of -mno-sse (clearly broken
> in at least one released GCC version), especially as the fix is so easy?
>
> Thanks,
>
> Ingo
Unfortunately part of this discussion gone private. Bringing it public.
This was not necessary a release version of gcc.
=====
The full story is that I spent quite some time debugging it with some
non-release gcc5 version a while ago, and then I was just sitting on
this patch. Now I am using release gcc6. I've just checked and the
kernel boots without these new flags. I thought that -mno-see does not
have to prevent newer SSE instructions, so this patch will save
somebody debugging in future. If the existing -mno-see should prevent
all SSE instructions, then I guess we don't need this patch.
And if not, then, no, I don't have a test case right now.
=====
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2016-06-27 19:06 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2016-06-22 17:37 [PATCH] x86: prevent gcc from emitting SSE into boot code Dmitry Vyukov
2016-06-22 20:17 ` Dmitry Vyukov
2016-06-27 18:53 ` Ingo Molnar
2016-06-27 18:58 ` Dmitry Vyukov
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