Messages in this thread Patch in this message | | | Date | Tue, 4 Feb 2014 20:16:00 -0800 | From | tip-bot for Borislav Petkov <> | Subject | [tip:x86/build] x86: Disable generation of traditional x87 instructions |
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Commit-ID: b399fe355b30d0102e7690c99e6f764ddfd32ec3 Gitweb: http://git.kernel.org/tip/b399fe355b30d0102e7690c99e6f764ddfd32ec3 Author: Borislav Petkov <bp@suse.de> AuthorDate: Wed, 5 Feb 2014 01:55:11 +0100 Committer: H. Peter Anvin <hpa@zytor.com> CommitDate: Tue, 4 Feb 2014 20:00:35 -0800
x86: Disable generation of traditional x87 instructions
We recently had the case where wrongly used floating-constant 'E' caused the generation of traditional x87 instructions in kernel code and wreaking all kinds of havoc.
Disable the generation of those too. This will save people a lot of time when trying to debug such issues by erroring out of the build instead of let them manifest themselves in very spectacular and happy-crappy ways at runtime.
We're using -mno-fp-ret-in-387 in addition to -mno-80387 (which is == -msoft-float) because, as the gcc manpage says:
On machines where a function returns floating-point results in the 80387 register stack, some floating-point opcodes may be emitted even if -msoft-float is used.
so we want to turn off *all* non-integer instructions involving any architectural FPU state, unless it is absolutely necessary (and those cases need special handling anyway).
Cc: Jiri Kosina <jkosina@suse.cz> Cc: Michael Matz <matz@suse.de> Cc: Michal Hocko <mhocko@suse.cz> Signed-off-by: Borislav Petkov <bp@suse.de> Link: http://lkml.kernel.org/r/1391561711-3023-1-git-send-email-bp@alien8.de Signed-off-by: H. Peter Anvin <hpa@zytor.com> --- arch/x86/Makefile | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/x86/Makefile b/arch/x86/Makefile index eeda43a..a414b14 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -82,8 +82,8 @@ else KBUILD_AFLAGS += -m64 KBUILD_CFLAGS += -m64 - # Don't autogenerate MMX or SSE instructions - KBUILD_CFLAGS += -mno-mmx -mno-sse + # Don't autogenerate traditional x87, MMX or SSE instructions + KBUILD_CFLAGS += -mno-mmx -mno-sse -mno-80387 -mno-fp-ret-in-387 # Use -mpreferred-stack-boundary=3 if supported. KBUILD_CFLAGS += $(call cc-option,-mpreferred-stack-boundary=3)
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