s390/ptrace: add support for PTRACE_SINGLEBLOCK

The PTRACE_SINGLEBLOCK option is used to get control whenever
the inferior has executed a successful branch. The PER option to
implement block stepping is successful-branching event, bit 32
in the PER-event mask.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/ptrace.h

@@ -83,6 +83,7 @@ struct per_struct_kernel {
  * These are defined as per linux/ptrace.h, which see.
  */
 #define arch_has_single_step()	(1)
+#define arch_has_block_step()	(1)
 
 #define user_mode(regs) (((regs)->psw.mask & PSW_MASK_PSTATE) != 0)
 #define instruction_pointer(regs) ((regs)->psw.addr & PSW_ADDR_INSN)

arch/s390/include/asm/thread_info.h

@@ -92,6 +92,7 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_MEMDIE		18	/* is terminating due to OOM killer */
 #define TIF_RESTORE_SIGMASK	19	/* restore signal mask in do_signal() */
 #define TIF_SINGLE_STEP		20	/* This task is single stepped */
+#define TIF_BLOCK_STEP		21	/* This task is block stepped */
 
 #define _TIF_SYSCALL		(1<<TIF_SYSCALL)
 #define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)

arch/s390/include/uapi/asm/ptrace.h

@@ -402,6 +402,12 @@ typedef struct
 #define PTRACE_DISABLE_TE	      0x5010
 #define PTRACE_TE_ABORT_RAND	      0x5011
 
+/*
+ * The numbers chosen here are somewhat arbitrary but absolutely MUST
+ * not overlap with any of the number assigned in <linux/ptrace.h>.
+ */
+#define PTRACE_SINGLEBLOCK	12	/* resume execution until next branch */
+
 /*
  * PT_PROT definition is loosely based on hppa bsd definition in
  * gdb/hppab-nat.c

arch/s390/kernel/ptrace.c

@@ -85,7 +85,10 @@ void update_cr_regs(struct task_struct *task)
 
 	/* merge TIF_SINGLE_STEP into user specified PER registers. */
 	if (test_tsk_thread_flag(task, TIF_SINGLE_STEP)) {
-		new.control |= PER_EVENT_IFETCH;
+		if (test_tsk_thread_flag(task, TIF_BLOCK_STEP))
+			new.control |= PER_EVENT_BRANCH;
+		else
+			new.control |= PER_EVENT_IFETCH;
 #ifdef CONFIG_64BIT
 		new.control |= PER_CONTROL_SUSPENSION;
 		new.control |= PER_EVENT_TRANSACTION_END;
@@ -107,14 +110,22 @@ void update_cr_regs(struct task_struct *task)
 
 void user_enable_single_step(struct task_struct *task)
 {
+	clear_tsk_thread_flag(task, TIF_BLOCK_STEP);
 	set_tsk_thread_flag(task, TIF_SINGLE_STEP);
 }
 
 void user_disable_single_step(struct task_struct *task)
 {
+	clear_tsk_thread_flag(task, TIF_BLOCK_STEP);
 	clear_tsk_thread_flag(task, TIF_SINGLE_STEP);
 }
 
+void user_enable_block_step(struct task_struct *task)
+{
+	set_tsk_thread_flag(task, TIF_SINGLE_STEP);
+	set_tsk_thread_flag(task, TIF_BLOCK_STEP);
+}
+
 /*
  * Called by kernel/ptrace.c when detaching..
  *