From b399fe355b30d0102e7690c99e6f764ddfd32ec3 Mon Sep 17 00:00:00 2001 From: Borislav Petkov Date: Wed, 5 Feb 2014 01:55:11 +0100 Subject: [PATCH] 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 Cc: Michael Matz Cc: Michal Hocko Signed-off-by: Borislav Petkov Link: http://lkml.kernel.org/r/1391561711-3023-1-git-send-email-bp@alien8.de Signed-off-by: H. Peter Anvin --- arch/x86/Makefile | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/Makefile b/arch/x86/Makefile index eeda43abed6e..a414b1471ffc 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)