* [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 += $(call cc-option,-fno-stack-protector) -- 2.8.0.rc3.226.g39d4020 ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] x86: prevent gcc from emitting SSE into boot code 2016-06-22 17:37 [PATCH] x86: prevent gcc from emitting SSE into boot code Dmitry Vyukov @ 2016-06-22 20:17 ` Dmitry Vyukov 2016-06-27 18:53 ` Ingo Molnar 0 siblings, 1 reply; 4+ messages in thread From: Dmitry Vyukov @ 2016-06-22 20:17 UTC (permalink / raw) To: H. Peter Anvin, Thomas Gleixner, Ingo Molnar, x86 Cc: LKML, Alexander Potapenko, Andrey Ryabinin, kasan-dev, Dmitry Vyukov On Wed, Jun 22, 2016 at 7:37 PM, Dmitry Vyukov <dvyukov@google.com> wrote: > Latest gcc manages to emit MOVDQA into boot code > which leads to crashes. Add more -mno-see flags. > > Signed-off-by: Dmitry Vyukov <dvyukov@google.com> > --- > arch/x86/boot/compressed/Makefile | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile > index f135688..7eaafb8 100644 > --- a/arch/x86/boot/compressed/Makefile > +++ b/arch/x86/boot/compressed/Makefile > @@ -31,7 +31,7 @@ KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING > cflags-$(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) -- links below jump to the message on this page -- 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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