[S390] kernel: Initialize register 14 when starting new CPU

When starting a new CPU we currently jump to start_secondary() without
setting register 14 (the return address) correctly. Therefore on the stack
frame for start_secondary an invalid return address is stored. This leads
to wrong stack back traces in kernel dumps.

Example:

 #00 [1f33fe48] cpu_idle at 10614a
 #01 [1f33fe90] start_secondary at 54fa88
 #02 [1f33feb8] (null) at 0                 <--- invalid

To fix this start_secondary() is called now with basr/brasl that sets
register 14 correctly. The output of the stack backtrace looks then
like the following:

 #00 [1f33fe48] cpu_idle at 10614a
 #01 [1f33fe90] start_secondary at 54fa88
 #02 [1f33feb8] restart_base at 54f41e      <--- correct

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

2 files changed, 2 insertions, 2 deletions

diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index 648f64239a9d..1b67fc6ebdc2 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -836,7 +836,7 @@ restart_base:
         stosm   __SF_EMPTY(%r15),0x04   # now we can turn dat on
         basr    %r14,0
         l       %r14,restart_addr-.(%r14)
-        br      %r14                    # branch to start_secondary
+        basr    %r14,%r14               # branch to start_secondary
 restart_addr:
         .long   start_secondary
         .align  8
diff --git a/arch/s390/kernel/entry64.S b/arch/s390/kernel/entry64.S
index 9d3603d6c511..9fd864563499 100644
--- a/arch/s390/kernel/entry64.S
+++ b/arch/s390/kernel/entry64.S
@@ -841,7 +841,7 @@ restart_base:
         mvc     __LC_SYSTEM_TIMER(8),__TI_system_timer(%r1)
         xc      __LC_STEAL_TIMER(8),__LC_STEAL_TIMER
         stosm   __SF_EMPTY(%r15),0x04   # now we can turn dat on
-        jg      start_secondary
+        brasl   %r14,start_secondary
         .align  8
 restart_vtime:
         .long   0x7fffffff,0xffffffff