[S390] fix system call parameter functions.

syscall_get_nr() currently returns a valid result only if the call
chain of the traced process includes do_syscall_trace_enter(). But
collect_syscall() can be called for any sleeping task, the result of
syscall_get_nr() in general is completely bogus.

To make syscall_get_nr() work for any sleeping task the traps field
in pt_regs is replace with svcnr - the system call number the process
is executing. If svcnr == 0 the process is not on a system call path.

The syscall_get_arguments and syscall_set_arguments use regs->gprs[2]
for the first system call parameter. This is incorrect since gprs[2]
may have been overwritten with the system call number if the call
chain includes do_syscall_trace_enter. Use regs->orig_gprs2 instead.

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

arch/s390/kernel/entry64.S

@@ -46,7 +46,7 @@ SP_R14	     =	STACK_FRAME_OVERHEAD + __PT_GPRS + 112
 SP_R15	     =	STACK_FRAME_OVERHEAD + __PT_GPRS + 120
 SP_ORIG_R2   =	STACK_FRAME_OVERHEAD + __PT_ORIG_GPR2
 SP_ILC	     =	STACK_FRAME_OVERHEAD + __PT_ILC
-SP_TRAP      =	STACK_FRAME_OVERHEAD + __PT_TRAP
+SP_SVCNR      =	STACK_FRAME_OVERHEAD + __PT_SVCNR
 SP_SIZE      =	STACK_FRAME_OVERHEAD + __PT_SIZE
 
 STACK_SHIFT = PAGE_SHIFT + THREAD_ORDER
@@ -171,11 +171,10 @@ _TIF_WORK_INT = (_TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_NEED_RESCHED | \
 	.macro	CREATE_STACK_FRAME psworg,savearea
 	aghi	%r15,-SP_SIZE		# make room for registers & psw
 	mvc	SP_PSW(16,%r15),0(%r12)	# move user PSW to stack
-	la	%r12,\psworg
 	stg	%r2,SP_ORIG_R2(%r15)	# store original content of gpr 2
-	icm	%r12,12,__LC_SVC_ILC
+	icm	%r12,3,__LC_SVC_ILC
 	stmg	%r0,%r11,SP_R0(%r15)	# store gprs %r0-%r11 to kernel stack
-	st	%r12,SP_ILC(%r15)
+	st	%r12,SP_SVCNR(%r15)
 	mvc	SP_R12(32,%r15),\savearea # move %r12-%r15 to stack
 	la	%r12,0
 	stg	%r12,__SF_BACKCHAIN(%r15)
@@ -250,16 +249,17 @@ sysc_update:
 #endif
 sysc_do_svc:
 	lg	%r9,__LC_THREAD_INFO	# load pointer to thread_info struct
-	slag	%r7,%r7,2	# *4 and test for svc 0
+	ltgr	%r7,%r7		# test for svc 0
 	jnz	sysc_nr_ok
 	# svc 0: system call number in %r1
 	cl	%r1,BASED(.Lnr_syscalls)
 	jnl	sysc_nr_ok
 	lgfr	%r7,%r1 	# clear high word in r1
-	slag	%r7,%r7,2	# svc 0: system call number in %r1
 sysc_nr_ok:
 	mvc	SP_ARGS(8,%r15),SP_R7(%r15)
 sysc_do_restart:
+	sth	%r7,SP_SVCNR(%r15)
+	sllg	%r7,%r7,2	# svc number * 4
 	larl	%r10,sys_call_table
 #ifdef CONFIG_COMPAT
 	tm	__TI_flags+5(%r9),(_TIF_31BIT>>16)  # running in 31 bit mode ?
@@ -363,7 +363,6 @@ sysc_notify_resume:
 sysc_restart:
 	ni	__TI_flags+7(%r9),255-_TIF_RESTART_SVC # clear TIF_RESTART_SVC
 	lg	%r7,SP_R2(%r15)		# load new svc number
-	slag	%r7,%r7,2		# *4
 	mvc	SP_R2(8,%r15),SP_ORIG_R2(%r15) # restore first argument
 	lmg	%r2,%r6,SP_R2(%r15)	# load svc arguments
 	j	sysc_do_restart 	# restart svc
@@ -372,9 +371,8 @@ sysc_restart:
 # _TIF_SINGLE_STEP is set, call do_single_step
 #
 sysc_singlestep:
-	ni	__TI_flags+7(%r9),255-_TIF_SINGLE_STEP # clear TIF_SINGLE_STEP
-	lhi	%r0,__LC_PGM_OLD_PSW
-	sth	%r0,SP_TRAP(%r15)	# set trap indication to pgm check
+	ni	__TI_flags+7(%r9),255-_TIF_SINGLE_STEP	# clear TIF_SINGLE_STEP
+	xc	SP_SVCNR(2,%r15),SP_SVCNR(%r15)		# clear svc number
 	la	%r2,SP_PTREGS(%r15)	# address of register-save area
 	larl	%r14,sysc_return	# load adr. of system return
 	jg	do_single_step		# branch to do_sigtrap
@@ -392,7 +390,7 @@ sysc_tracesys:
 	lghi	%r0,NR_syscalls
 	clgr	%r0,%r2
 	jnh	sysc_tracenogo
-	slag	%r7,%r2,2		# *4
+	sllg	%r7,%r2,2		# svc number *4
 	lgf	%r8,0(%r7,%r10)
 sysc_tracego:
 	lmg	%r3,%r6,SP_R3(%r15)
@@ -567,8 +565,7 @@ pgm_svcper:
 # per was called from kernel, must be kprobes
 #
 kernel_per:
-	lhi	%r0,__LC_PGM_OLD_PSW
-	sth	%r0,SP_TRAP(%r15)	# set trap indication to pgm check
+	xc	SP_SVCNR(2,%r15),SP_SVCNR(%r15)	# clear svc number
 	la	%r2,SP_PTREGS(%r15)	# address of register-save area
 	larl	%r14,sysc_restore	# load adr. of system ret, no work
 	jg	do_single_step		# branch to do_single_step