[S390] virtual cpu accounting vs. machine checks.

If a machine checks interrupts the external or the i/o interrupt
handler before they have completed the cpu time calculations, the
accounting goes wrong. After the cpu returned from the machine check
handler to the interrupted interrupt handler, a negative cpu time delta
can occur.  If the accumulated cpu time in lowcore is small enough
this value can get negative as well. The next jiffy interrupt will pick
up that negative value, shift it by 12 and add the now huge positive
value to the cpu time of the process.
To solve this the machine check handler is modified not to change any
of the timestamps in the lowcore if the machine check interrupted kernel
context.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

2 files changed, 116 insertions, 41 deletions

diff --git a/arch/s390/kernel/entry.S b/arch/s390/kernel/entry.S
index b2448487854c..74d80c3bba80 100644
--- a/arch/s390/kernel/entry.S
+++ b/arch/s390/kernel/entry.S
@@ -93,13 +93,22 @@ STACK_SIZE  = 1 << STACK_SHIFT
         l       %r13,__LC_SVC_NEW_PSW+4 # load &system_call to %r13
         .endm
 
-        .macro  SAVE_ALL psworg,savearea,sync
+        .macro  SAVE_ALL_SYNC psworg,savearea
         la      %r12,\psworg
-        .if     \sync
         tm      \psworg+1,0x01          # test problem state bit
         bz      BASED(2f)               # skip stack setup save
         l       %r15,__LC_KERNEL_STACK  # problem state -> load ksp
-        .else
+#ifdef CONFIG_CHECK_STACK
+        b       BASED(3f)
+2:      tml     %r15,STACK_SIZE - CONFIG_STACK_GUARD
+        bz      BASED(stack_overflow)
+3:
+#endif
+2:
+        .endm
+
+        .macro  SAVE_ALL_ASYNC psworg,savearea
+        la      %r12,\psworg
         tm      \psworg+1,0x01          # test problem state bit
         bnz     BASED(1f)               # from user -> load async stack
         clc     \psworg+4(4),BASED(.Lcritical_end)
@@ -115,7 +124,6 @@ STACK_SIZE  = 1 << STACK_SHIFT
         sra     %r14,STACK_SHIFT
         be      BASED(2f)
 1:      l       %r15,__LC_ASYNC_STACK
-        .endif
 #ifdef CONFIG_CHECK_STACK
         b       BASED(3f)
 2:      tml     %r15,STACK_SIZE - CONFIG_STACK_GUARD
@@ -196,7 +204,7 @@ system_call:
         STORE_TIMER __LC_SYNC_ENTER_TIMER
 sysc_saveall:
         SAVE_ALL_BASE __LC_SAVE_AREA
-        SAVE_ALL __LC_SVC_OLD_PSW,__LC_SAVE_AREA,1
+        SAVE_ALL_SYNC __LC_SVC_OLD_PSW,__LC_SAVE_AREA
         CREATE_STACK_FRAME __LC_SVC_OLD_PSW,__LC_SAVE_AREA
         lh      %r7,0x8a          # get svc number from lowcore
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
@@ -425,7 +433,7 @@ pgm_check_handler:
         SAVE_ALL_BASE __LC_SAVE_AREA
         tm      __LC_PGM_INT_CODE+1,0x80 # check whether we got a per exception
         bnz     BASED(pgm_per)           # got per exception -> special case
-        SAVE_ALL __LC_PGM_OLD_PSW,__LC_SAVE_AREA,1
+        SAVE_ALL_SYNC __LC_PGM_OLD_PSW,__LC_SAVE_AREA
         CREATE_STACK_FRAME __LC_PGM_OLD_PSW,__LC_SAVE_AREA
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
         tm      SP_PSW+1(%r15),0x01     # interrupting from user ?
@@ -464,7 +472,7 @@ pgm_per:
 # Normal per exception
 #
 pgm_per_std:
-        SAVE_ALL __LC_PGM_OLD_PSW,__LC_SAVE_AREA,1
+        SAVE_ALL_SYNC __LC_PGM_OLD_PSW,__LC_SAVE_AREA
         CREATE_STACK_FRAME __LC_PGM_OLD_PSW,__LC_SAVE_AREA
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
         tm      SP_PSW+1(%r15),0x01     # interrupting from user ?
@@ -490,7 +498,7 @@ pgm_no_vtime2:
 # it was a single stepped SVC that is causing all the trouble
 #
 pgm_svcper:
-        SAVE_ALL __LC_SVC_OLD_PSW,__LC_SAVE_AREA,1
+        SAVE_ALL_SYNC __LC_SVC_OLD_PSW,__LC_SAVE_AREA
         CREATE_STACK_FRAME __LC_SVC_OLD_PSW,__LC_SAVE_AREA
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
         tm      SP_PSW+1(%r15),0x01     # interrupting from user ?
@@ -519,7 +527,7 @@ io_int_handler:
         STORE_TIMER __LC_ASYNC_ENTER_TIMER
         stck    __LC_INT_CLOCK
         SAVE_ALL_BASE __LC_SAVE_AREA+16
-        SAVE_ALL __LC_IO_OLD_PSW,__LC_SAVE_AREA+16,0
+        SAVE_ALL_ASYNC __LC_IO_OLD_PSW,__LC_SAVE_AREA+16
         CREATE_STACK_FRAME __LC_IO_OLD_PSW,__LC_SAVE_AREA+16
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
         tm      SP_PSW+1(%r15),0x01     # interrupting from user ?
@@ -631,7 +639,7 @@ ext_int_handler:
         STORE_TIMER __LC_ASYNC_ENTER_TIMER
         stck    __LC_INT_CLOCK
         SAVE_ALL_BASE __LC_SAVE_AREA+16
-        SAVE_ALL __LC_EXT_OLD_PSW,__LC_SAVE_AREA+16,0
+        SAVE_ALL_ASYNC __LC_EXT_OLD_PSW,__LC_SAVE_AREA+16
         CREATE_STACK_FRAME __LC_EXT_OLD_PSW,__LC_SAVE_AREA+16
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
         tm      SP_PSW+1(%r15),0x01     # interrupting from user ?
@@ -657,21 +665,31 @@ __critical_end:
         .globl mcck_int_handler
 mcck_int_handler:
         spt     __LC_CPU_TIMER_SAVE_AREA        # revalidate cpu timer
-        mvc     __LC_ASYNC_ENTER_TIMER(8),__LC_CPU_TIMER_SAVE_AREA
         lm      %r0,%r15,__LC_GPREGS_SAVE_AREA  # revalidate gprs
         SAVE_ALL_BASE __LC_SAVE_AREA+32
         la      %r12,__LC_MCK_OLD_PSW
         tm      __LC_MCCK_CODE,0x80     # system damage?
         bo      BASED(mcck_int_main)    # yes -> rest of mcck code invalid
-        tm      __LC_MCCK_CODE+5,0x02   # stored cpu timer value valid?
-        bo      BASED(0f)
-        spt     __LC_LAST_UPDATE_TIMER  # revalidate cpu timer
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
-        mvc     __LC_ASYNC_ENTER_TIMER(8),__LC_LAST_UPDATE_TIMER
-        mvc     __LC_SYNC_ENTER_TIMER(8),__LC_LAST_UPDATE_TIMER
-        mvc     __LC_EXIT_TIMER(8),__LC_LAST_UPDATE_TIMER
+        mvc     __LC_SAVE_AREA+52(8),__LC_ASYNC_ENTER_TIMER
+        mvc     __LC_ASYNC_ENTER_TIMER(8),__LC_CPU_TIMER_SAVE_AREA
+        tm      __LC_MCCK_CODE+5,0x02   # stored cpu timer value valid?
+        bo      BASED(1f)
+        la      %r14,__LC_SYNC_ENTER_TIMER
+        clc     0(8,%r14),__LC_ASYNC_ENTER_TIMER
+        bl      BASED(0f)
+        la      %r14,__LC_ASYNC_ENTER_TIMER
+0:      clc     0(8,%r14),__LC_EXIT_TIMER
+        bl      BASED(0f)
+        la      %r14,__LC_EXIT_TIMER
+0:      clc     0(8,%r14),__LC_LAST_UPDATE_TIMER
+        bl      BASED(0f)
+        la      %r14,__LC_LAST_UPDATE_TIMER
+0:      spt     0(%r14)
+        mvc     __LC_ASYNC_ENTER_TIMER(8),0(%r14)
+1:
 #endif
-0:      tm      __LC_MCCK_CODE+2,0x09   # mwp + ia of old psw valid?
+        tm      __LC_MCCK_CODE+2,0x09   # mwp + ia of old psw valid?
         bno     BASED(mcck_int_main)    # no -> skip cleanup critical
         tm      __LC_MCK_OLD_PSW+1,0x01 # test problem state bit
         bnz     BASED(mcck_int_main)    # from user -> load async stack
@@ -691,7 +709,7 @@ mcck_int_main:
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
         tm      __LC_MCCK_CODE+2,0x08   # mwp of old psw valid?
         bno     BASED(mcck_no_vtime)    # no -> skip cleanup critical
-        tm      __LC_MCK_OLD_PSW+1,0x01 # interrupting from user ?
+        tm      SP_PSW+1(%r15),0x01     # interrupting from user ?
         bz      BASED(mcck_no_vtime)
         UPDATE_VTIME __LC_EXIT_TIMER,__LC_ASYNC_ENTER_TIMER,__LC_USER_TIMER
         UPDATE_VTIME __LC_LAST_UPDATE_TIMER,__LC_EXIT_TIMER,__LC_SYSTEM_TIMER
@@ -715,6 +733,20 @@ mcck_no_vtime:
         l       %r1,BASED(.Ls390_handle_mcck)
         basr    %r14,%r1                # call machine check handler
 mcck_return:
+        mvc     __LC_RETURN_MCCK_PSW(8),SP_PSW(%r15) # move return PSW
+        ni      __LC_RETURN_MCCK_PSW+1,0xfd # clear wait state bit
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING
+        mvc     __LC_ASYNC_ENTER_TIMER(8),__LC_SAVE_AREA+52
+        tm      __LC_RETURN_MCCK_PSW+1,0x01 # returning to user ?
+        bno     BASED(0f)
+        lm      %r0,%r15,SP_R0(%r15)    # load gprs 0-15
+        stpt    __LC_EXIT_TIMER
+        lpsw    __LC_RETURN_MCCK_PSW    # back to caller
+0:
+#endif
+        lm      %r0,%r15,SP_R0(%r15)    # load gprs 0-15
+        lpsw    __LC_RETURN_MCCK_PSW    # back to caller
+
         RESTORE_ALL __LC_RETURN_MCCK_PSW,0
 
 #ifdef CONFIG_SMP
@@ -781,6 +813,8 @@ cleanup_table_sysc_leave:
         .long   sysc_leave + 0x80000000, sysc_work_loop + 0x80000000
 cleanup_table_sysc_work_loop:
         .long   sysc_work_loop + 0x80000000, sysc_reschedule + 0x80000000
+cleanup_table_io_return:
+        .long   io_return + 0x80000000, io_leave + 0x80000000
 cleanup_table_io_leave:
         .long   io_leave + 0x80000000, io_done + 0x80000000
 cleanup_table_io_work_loop:
@@ -807,6 +841,11 @@ cleanup_critical:
         clc     4(4,%r12),BASED(cleanup_table_sysc_work_loop+4)
         bl      BASED(cleanup_sysc_return)
 0:
+        clc     4(4,%r12),BASED(cleanup_table_io_return)
+        bl      BASED(0f)
+        clc     4(4,%r12),BASED(cleanup_table_io_return+4)
+        bl      BASED(cleanup_io_return)
+0:
         clc     4(4,%r12),BASED(cleanup_table_io_leave)
         bl      BASED(0f)
         clc     4(4,%r12),BASED(cleanup_table_io_leave+4)
@@ -839,7 +878,7 @@ cleanup_system_call:
         mvc     __LC_SAVE_AREA(16),0(%r12)
 0:      st      %r13,4(%r12)
         st      %r12,__LC_SAVE_AREA+48  # argh
-        SAVE_ALL __LC_SVC_OLD_PSW,__LC_SAVE_AREA,1
+        SAVE_ALL_SYNC __LC_SVC_OLD_PSW,__LC_SAVE_AREA
         CREATE_STACK_FRAME __LC_SVC_OLD_PSW,__LC_SAVE_AREA
         l       %r12,__LC_SAVE_AREA+48  # argh
         st      %r15,12(%r12)
diff --git a/arch/s390/kernel/entry64.S b/arch/s390/kernel/entry64.S
index 2ac095bc0e25..21e601d56139 100644
--- a/arch/s390/kernel/entry64.S
+++ b/arch/s390/kernel/entry64.S
@@ -87,13 +87,22 @@ _TIF_WORK_INT = (_TIF_SIGPENDING | _TIF_RESTORE_SIGMASK | _TIF_NEED_RESCHED | \
         larl    %r13,system_call
         .endm
 
-        .macro  SAVE_ALL psworg,savearea,sync
+        .macro  SAVE_ALL_SYNC psworg,savearea
         la      %r12,\psworg
-        .if     \sync
         tm      \psworg+1,0x01          # test problem state bit
         jz      2f                      # skip stack setup save
         lg      %r15,__LC_KERNEL_STACK  # problem state -> load ksp
-        .else
+#ifdef CONFIG_CHECK_STACK
+        j       3f
+2:      tml     %r15,STACK_SIZE - CONFIG_STACK_GUARD
+        jz      stack_overflow
+3:
+#endif
+2:
+        .endm
+
+        .macro  SAVE_ALL_ASYNC psworg,savearea
+        la      %r12,\psworg
         tm      \psworg+1,0x01          # test problem state bit
         jnz     1f                      # from user -> load kernel stack
         clc     \psworg+8(8),BASED(.Lcritical_end)
@@ -108,7 +117,6 @@ _TIF_WORK_INT = (_TIF_SIGPENDING | _TIF_RESTORE_SIGMASK | _TIF_NEED_RESCHED | \
         srag    %r14,%r14,STACK_SHIFT
         jz      2f
 1:      lg      %r15,__LC_ASYNC_STACK   # load async stack
-        .endif
 #ifdef CONFIG_CHECK_STACK
         j       3f
 2:      tml     %r15,STACK_SIZE - CONFIG_STACK_GUARD
@@ -187,7 +195,7 @@ system_call:
         STORE_TIMER __LC_SYNC_ENTER_TIMER
 sysc_saveall:
         SAVE_ALL_BASE __LC_SAVE_AREA
-        SAVE_ALL __LC_SVC_OLD_PSW,__LC_SAVE_AREA,1
+        SAVE_ALL_SYNC __LC_SVC_OLD_PSW,__LC_SAVE_AREA
         CREATE_STACK_FRAME __LC_SVC_OLD_PSW,__LC_SAVE_AREA
         llgh    %r7,__LC_SVC_INT_CODE # get svc number from lowcore
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
@@ -446,7 +454,7 @@ pgm_check_handler:
         SAVE_ALL_BASE __LC_SAVE_AREA
         tm      __LC_PGM_INT_CODE+1,0x80 # check whether we got a per exception
         jnz     pgm_per                  # got per exception -> special case
-        SAVE_ALL __LC_PGM_OLD_PSW,__LC_SAVE_AREA,1
+        SAVE_ALL_SYNC __LC_PGM_OLD_PSW,__LC_SAVE_AREA
         CREATE_STACK_FRAME __LC_PGM_OLD_PSW,__LC_SAVE_AREA
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
         tm      SP_PSW+1(%r15),0x01     # interrupting from user ?
@@ -485,7 +493,7 @@ pgm_per:
 # Normal per exception
 #
 pgm_per_std:
-        SAVE_ALL __LC_PGM_OLD_PSW,__LC_SAVE_AREA,1
+        SAVE_ALL_SYNC __LC_PGM_OLD_PSW,__LC_SAVE_AREA
         CREATE_STACK_FRAME __LC_PGM_OLD_PSW,__LC_SAVE_AREA
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
         tm      SP_PSW+1(%r15),0x01     # interrupting from user ?
@@ -511,7 +519,7 @@ pgm_no_vtime2:
 # it was a single stepped SVC that is causing all the trouble
 #
 pgm_svcper:
-        SAVE_ALL __LC_SVC_OLD_PSW,__LC_SAVE_AREA,1
+        SAVE_ALL_SYNC __LC_SVC_OLD_PSW,__LC_SAVE_AREA
         CREATE_STACK_FRAME __LC_SVC_OLD_PSW,__LC_SAVE_AREA
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
         tm      SP_PSW+1(%r15),0x01     # interrupting from user ?
@@ -539,7 +547,7 @@ io_int_handler:
         STORE_TIMER __LC_ASYNC_ENTER_TIMER
         stck    __LC_INT_CLOCK
         SAVE_ALL_BASE __LC_SAVE_AREA+32
-        SAVE_ALL __LC_IO_OLD_PSW,__LC_SAVE_AREA+32,0
+        SAVE_ALL_ASYNC __LC_IO_OLD_PSW,__LC_SAVE_AREA+32
         CREATE_STACK_FRAME __LC_IO_OLD_PSW,__LC_SAVE_AREA+32
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
         tm      SP_PSW+1(%r15),0x01     # interrupting from user ?
@@ -647,7 +655,7 @@ ext_int_handler:
         STORE_TIMER __LC_ASYNC_ENTER_TIMER
         stck    __LC_INT_CLOCK
         SAVE_ALL_BASE __LC_SAVE_AREA+32
-        SAVE_ALL __LC_EXT_OLD_PSW,__LC_SAVE_AREA+32,0
+        SAVE_ALL_ASYNC __LC_EXT_OLD_PSW,__LC_SAVE_AREA+32
         CREATE_STACK_FRAME __LC_EXT_OLD_PSW,__LC_SAVE_AREA+32
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
         tm      SP_PSW+1(%r15),0x01     # interrupting from user ?
@@ -672,21 +680,32 @@ __critical_end:
 mcck_int_handler:
         la      %r1,4095                # revalidate r1
         spt     __LC_CPU_TIMER_SAVE_AREA-4095(%r1)      # revalidate cpu timer
-        mvc     __LC_ASYNC_ENTER_TIMER(8),__LC_CPU_TIMER_SAVE_AREA-4095(%r1)
         lmg     %r0,%r15,__LC_GPREGS_SAVE_AREA-4095(%r1)# revalidate gprs
         SAVE_ALL_BASE __LC_SAVE_AREA+64
         la      %r12,__LC_MCK_OLD_PSW
         tm      __LC_MCCK_CODE,0x80     # system damage?
         jo      mcck_int_main           # yes -> rest of mcck code invalid
-        tm      __LC_MCCK_CODE+5,0x02   # stored cpu timer value valid?
-        jo      0f
-        spt     __LC_LAST_UPDATE_TIMER
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
-        mvc     __LC_ASYNC_ENTER_TIMER(8),__LC_LAST_UPDATE_TIMER
-        mvc     __LC_SYNC_ENTER_TIMER(8),__LC_LAST_UPDATE_TIMER
-        mvc     __LC_EXIT_TIMER(8),__LC_LAST_UPDATE_TIMER
+        la      %r14,4095
+        mvc     __LC_SAVE_AREA+104(8),__LC_ASYNC_ENTER_TIMER
+        mvc     __LC_ASYNC_ENTER_TIMER(8),__LC_CPU_TIMER_SAVE_AREA-4095(%r14)
+        tm      __LC_MCCK_CODE+5,0x02   # stored cpu timer value valid?
+        jo      1f
+        la      %r14,__LC_SYNC_ENTER_TIMER
+        clc     0(8,%r14),__LC_ASYNC_ENTER_TIMER
+        jl      0f
+        la      %r14,__LC_ASYNC_ENTER_TIMER
+0:      clc     0(8,%r14),__LC_EXIT_TIMER
+        jl      0f
+        la      %r14,__LC_EXIT_TIMER
+0:      clc     0(8,%r14),__LC_LAST_UPDATE_TIMER
+        jl      0f
+        la      %r14,__LC_LAST_UPDATE_TIMER
+0:      spt     0(%r14)
+        mvc     __LC_ASYNC_ENTER_TIMER(8),0(%r14)
+1:
 #endif
-0:      tm      __LC_MCCK_CODE+2,0x09   # mwp + ia of old psw valid?
+        tm      __LC_MCCK_CODE+2,0x09   # mwp + ia of old psw valid?
         jno     mcck_int_main           # no -> skip cleanup critical
         tm      __LC_MCK_OLD_PSW+1,0x01 # test problem state bit
         jnz     mcck_int_main           # from user -> load kernel stack
@@ -705,7 +724,7 @@ mcck_int_main:
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
         tm      __LC_MCCK_CODE+2,0x08   # mwp of old psw valid?
         jno     mcck_no_vtime           # no -> no timer update
-        tm      __LC_MCK_OLD_PSW+1,0x01 # interrupting from user ?
+        tm      SP_PSW+1(%r15),0x01     # interrupting from user ?
         jz      mcck_no_vtime
         UPDATE_VTIME __LC_EXIT_TIMER,__LC_ASYNC_ENTER_TIMER,__LC_USER_TIMER
         UPDATE_VTIME __LC_LAST_UPDATE_TIMER,__LC_EXIT_TIMER,__LC_SYSTEM_TIMER
@@ -727,7 +746,17 @@ mcck_no_vtime:
         jno     mcck_return
         brasl   %r14,s390_handle_mcck
 mcck_return:
-        RESTORE_ALL __LC_RETURN_MCCK_PSW,0
+        mvc     __LC_RETURN_MCCK_PSW(16),SP_PSW(%r15) # move return PSW
+        ni      __LC_RETURN_MCCK_PSW+1,0xfd # clear wait state bit
+        lmg     %r0,%r15,SP_R0(%r15)    # load gprs 0-15
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING
+        mvc     __LC_ASYNC_ENTER_TIMER(8),__LC_SAVE_AREA+104
+        tm      __LC_RETURN_MCCK_PSW+1,0x01 # returning to user ?
+        jno     0f
+        stpt    __LC_EXIT_TIMER
+0:
+#endif
+        lpswe   __LC_RETURN_MCCK_PSW    # back to caller
 
 #ifdef CONFIG_SMP
 /*
@@ -789,6 +818,8 @@ cleanup_table_sysc_leave:
         .quad   sysc_leave, sysc_work_loop
 cleanup_table_sysc_work_loop:
         .quad   sysc_work_loop, sysc_reschedule
+cleanup_table_io_return:
+        .quad   io_return, io_leave
 cleanup_table_io_leave:
         .quad   io_leave, io_done
 cleanup_table_io_work_loop:
@@ -815,6 +846,11 @@ cleanup_critical:
         clc     8(8,%r12),BASED(cleanup_table_sysc_work_loop+8)
         jl      cleanup_sysc_return
 0:
+        clc     8(8,%r12),BASED(cleanup_table_io_return)
+        jl      0f
+        clc     8(8,%r12),BASED(cleanup_table_io_return+8)
+        jl      cleanup_io_return
+0:
         clc     8(8,%r12),BASED(cleanup_table_io_leave)
         jl      0f
         clc     8(8,%r12),BASED(cleanup_table_io_leave+8)
@@ -847,7 +883,7 @@ cleanup_system_call:
         mvc     __LC_SAVE_AREA(32),0(%r12)
 0:      stg     %r13,8(%r12)
         stg     %r12,__LC_SAVE_AREA+96  # argh
-        SAVE_ALL __LC_SVC_OLD_PSW,__LC_SAVE_AREA,1
+        SAVE_ALL_SYNC __LC_SVC_OLD_PSW,__LC_SAVE_AREA
         CREATE_STACK_FRAME __LC_SVC_OLD_PSW,__LC_SAVE_AREA
         lg      %r12,__LC_SAVE_AREA+96  # argh
         stg     %r15,24(%r12)