lkml.org 
[lkml]   [2014]   [Feb]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] x86: Disable generation of traditional x87 instructions
Date
From: Borislav Petkov <bp@suse.de>

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>
---
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)
--
1.8.5.2.192.g7794a68


\
 
 \ /
  Last update: 2014-02-05 02:21    [W:0.869 / U:0.020 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site