xtensa: implement syscall tracepoints

Add TIF_SYSCALL_TRACEPOINT flag definition; add _TIF_SYSCALL_TRACEPOINT
to _TIF_WORK_MASK. Call trace_sys_enter from do_syscall_trace_enter and
trace_sys_exit from do_syscall_trace_leave when TIF_SYSCALL_TRACEPOINT
flag is set.
Add declaration of sys_call_table to arch/xtensa/include/asm/syscall.h
Add definition of NR_syscalls to arch/xtensa/include/asm/unistd.h
Select HAVE_SYSCALL_TRACEPOINTS.

This change allows tracing each syscall entry and exit through the
ftrace mechanism.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/kernel/ptrace.c

@@ -27,6 +27,9 @@
 #include <linux/tracehook.h>
 #include <linux/uaccess.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/syscalls.h>
+
 #include <asm/coprocessor.h>
 #include <asm/elf.h>
 #include <asm/page.h>
@@ -545,12 +548,17 @@ void do_syscall_trace_enter(struct pt_regs *regs)
 	    tracehook_report_syscall_entry(regs))
 		regs->syscall = NO_SYSCALL;
 
+	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
+		trace_sys_enter(regs, syscall_get_nr(current, regs));
 }
 
 void do_syscall_trace_leave(struct pt_regs *regs)
 {
 	int step;
 
+	if (test_thread_flag(TIF_SYSCALL_TRACEPOINT))
+		trace_sys_exit(regs, regs_return_value(regs));
+
 	step = test_thread_flag(TIF_SINGLESTEP);
 
 	if (step || test_thread_flag(TIF_SYSCALL_TRACE))

arch/xtensa/kernel/syscall.c

@@ -28,8 +28,6 @@
 #include <linux/sched/mm.h>
 #include <linux/shm.h>
 
-typedef void (*syscall_t)(void);
-
 syscall_t sys_call_table[__NR_syscalls] /* FIXME __cacheline_aligned */= {
 	[0 ... __NR_syscalls - 1] = (syscall_t)&sys_ni_syscall,