Re: [BUG] Kernel built for i586 chip crashes instantly at boot time (CMOV instructions)

["H. Peter Anvin" <hpa@zytor.com>]

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On 12/18/2009 07:28 AM, Chris Rankin wrote:
> Hi,
> 
> I have been trying to build a 2.6.31.x kernel with Fedora 12's gcc compiler, and have discovered that this kernel crashes instantly at boot-time due to a pair of CMOV instructions in arch/x86/boot/compressed/misc.o. According to "make V=1", the command used to compile misc.c is:
> 
>   gcc -Wp,-MD,arch/x86/boot/compressed/.misc.o.d  -nostdinc -isystem /usr/lib/gcc/i686-redhat-linux/4.4.2/include -Iinclude -Iinclude2 -I/home/chris/LINUX/linux-2.6.31/include -I/home/chris/LINUX/linux-2.6.31/arch/x86/include -include include/linux/autoconf.h  -I/home/chris/LINUX/linux-2.6.31/arch/x86/boot/compressed -Iarch/x86/boot/compressed -D__KERNEL__ -m32 -D__KERNEL__ -O2 -fno-strict-aliasing -fPIC -DDISABLE_BRANCH_PROFILING -ffreestanding -fno-stack-protector   -D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(misc)"  -D"KBUILD_MODNAME=KBUILD_STR(misc)"  -c -o arch/x86/boot/compressed/misc.o /home/chris/LINUX/linux-2.6.31/arch/x86/boot/compressed/misc.c
> 
> which apparently uses gcc's default architecture. However, Fedora has recently changed its gcc default architecture from i586 to i686, and so I end up with a pair on invalid instructions in my kernel binary.
> 

Does this patch work for you?

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.


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diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index f8ed065..f25bbd3 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -9,6 +9,7 @@ targets := vmlinux.lds vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinu
 KBUILD_CFLAGS := -m$(BITS) -D__KERNEL__ $(LINUX_INCLUDE) -O2
 KBUILD_CFLAGS += -fno-strict-aliasing -fPIC
 KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING
+cflags-$(CONFIG_X86_32) := -march=i386
 cflags-$(CONFIG_X86_64) := -mcmodel=small
 KBUILD_CFLAGS += $(cflags-y)
 KBUILD_CFLAGS += $(call cc-option,-ffreestanding)