[PATCH 3.12 06/82] s390/sclp: clear upper register halves in _sclp_print_early

From: Jiri Slaby
Date: Mon Aug 24 2015 - 05:37:27 EST


From: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>

3.12-stable 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
_sclp_servc.

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
driver.

Signed-off-by: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
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 29bd7bec4176..1ecd47b5e250 100644
--- 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
.Lesa2:
#endif
lr %r10,%r2 # save string pointer
@@ -299,6 +301,8 @@ ENTRY(_sclp_print_early)
#endif
lm %r6,%r15,120(%r15) # restore registers
br %r14
+.Lzeroes:
+ .fill 64,4,0

.LwritedataS4:
.long 0x00760005 # SCLP command for write data
--
2.5.0

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