s390/sclp: clear upper register halves in _sclp_print_early

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@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/s390/kernel/sclp.S b/arch/s390/kernel/sclp.S
index 29bd7bec41768c328c17285b4876c428727d41d0..1ecd47b5e250780cd438a968da802b6ce1305392 100644 (file)
--- 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