[PATCH 3.4 016/107] s390/sclp: clear upper register halves in _sclp_print_early

From: lizf
Date: Wed Mar 16 2016 - 04:41:51 EST

From: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>

3.4.111-rc1 review patch. If anyone has any objections, please let me know.


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: Zefan Li <lizefan@xxxxxxxxxx>
arch/s390/kernel/sclp.S | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/arch/s390/kernel/sclp.S b/arch/s390/kernel/sclp.S
index 95792d8..51ca1c3 100644
--- a/arch/s390/kernel/sclp.S
+++ b/arch/s390/kernel/sclp.S
@@ -270,6 +270,8 @@ 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
@@ -293,6 +295,8 @@ ENTRY(_sclp_print_early)
lm %r6,%r15,120(%r15) # restore registers
br %r14
+ .fill 64,4,0

.long 0x00760005 # SCLP command for write data