[PATCH 3.10 03/26] s390/sclp: clear upper register halves in _sclp_print_early

From: Greg Kroah-Hartman
Date: Sat Aug 08 2015 - 18:49:26 EST

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


From: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>

commit f9c87a6f46d508eae0d9ae640be98d50f237f827 upstream.

If the kernel is compiled with gcc 5.1 and the XZ compression option
the decompress_kernel function calls _sclp_print_early in 64-bit mode
while the content of the upper register half of %r6 is non-zero.
This causes a specification exception on the servc instruction in

The _sclp_print_early function saves and restores the upper registers
halves but it fails to clear them for the 31-bit code of the mini sclp

Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

arch/s390/kernel/sclp.S | 4 ++++
1 file changed, 4 insertions(+)

--- a/arch/s390/kernel/sclp.S
+++ b/arch/s390/kernel/sclp.S
@@ -276,6 +276,8 @@ ENTRY(_sclp_print_early)
jno .Lesa2
ahi %r15,-80
stmh %r6,%r15,96(%r15) # store upper register halves
+ basr %r13,0
+ lmh %r0,%r15,.Lzeroes-.(%r13) # clear upper register halves
lr %r10,%r2 # save string pointer
@@ -299,6 +301,8 @@ ENTRY(_sclp_print_early)
lm %r6,%r15,120(%r15) # restore registers
br %r14
+ .fill 64,4,0

.long 0x00760005 # SCLP command for write data

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