[PATCH 3.13.y-ckt 14/96] s390/boot/decompression: disable floating point in decompressor

From: Kamal Mostafa
Date: Fri Nov 13 2015 - 16:50:18 EST

3.13.11-ckt30 -stable review patch. If anyone has any objections, please let me know.


From: Christian Borntraeger <borntraeger@xxxxxxxxxx>

commit adc0b7fbf6fe9967505c0254d9535ec7288186ae upstream.

my gcc 5.1 used an ldgr instruction with a register != 0,2,4,6 for
spilling/filling into a floating point register in our decompressor.

This will cause an AFP-register data exception as the decompressor
did not setup the additional floating point registers via cr0.
That causes a program check loop that looked like a hang with
one "Uncompressing Linux... " message (directly booted via kvm)
or a loop of "Uncompressing Linux... " messages (when booted via
zipl boot loader).

The offending code in my build was

48e400: e3 c0 af ff ff 71 lay %r12,-1(%r10)
-->48e406: b3 c1 00 1c ldgr %f1,%r12
48e40a: ec 6c 01 22 02 7f clij %r6,2,12,0x48e64e

but gcc could do spilling into an fpr at any function. We can
simply disable floating point support at that early stage.

Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
Acked-by: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
arch/s390/boot/compressed/Makefile | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/s390/boot/compressed/Makefile b/arch/s390/boot/compressed/Makefile
index f90d1fc..f70b232 100644
--- a/arch/s390/boot/compressed/Makefile
+++ b/arch/s390/boot/compressed/Makefile
@@ -12,7 +12,7 @@ targets += misc.o piggy.o sizes.h head$(BITS).o

-KBUILD_CFLAGS += $(cflags-y) -fno-delete-null-pointer-checks
+KBUILD_CFLAGS += $(cflags-y) -fno-delete-null-pointer-checks -msoft-float
KBUILD_CFLAGS += $(call cc-option,-mpacked-stack)
KBUILD_CFLAGS += $(call cc-option,-ffreestanding)


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