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/Kconfig

@@ -29,6 +29,7 @@ config XTENSA
 	select HAVE_OPROFILE
 	select HAVE_PERF_EVENTS
 	select HAVE_STACKPROTECTOR
+	select HAVE_SYSCALL_TRACEPOINTS
 	select IRQ_DOMAIN
 	select MODULES_USE_ELF_RELA
 	select PERF_USE_VMALLOC

arch/xtensa/include/asm/ptrace.h

@@ -102,6 +102,11 @@ struct pt_regs {
 
 #define user_stack_pointer(regs) ((regs)->areg[1])
 
+static inline unsigned long regs_return_value(struct pt_regs *regs)
+{
+	return regs->areg[2];
+}
+
 #else	/* __ASSEMBLY__ */
 
 # include <asm/asm-offsets.h>

arch/xtensa/include/asm/syscall.h

@@ -19,6 +19,9 @@ static inline int syscall_get_arch(void)
 	return AUDIT_ARCH_XTENSA;
 }
 
+typedef void (*syscall_t)(void);
+extern syscall_t sys_call_table[];
+
 static inline long syscall_get_nr(struct task_struct *task,
 				  struct pt_regs *regs)
 {

arch/xtensa/include/asm/thread_info.h

@@ -106,6 +106,7 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_SIGPENDING		1	/* signal pending */
 #define TIF_NEED_RESCHED	2	/* rescheduling necessary */
 #define TIF_SINGLESTEP		3	/* restore singlestep on return to user mode */
+#define TIF_SYSCALL_TRACEPOINT	4	/* syscall tracepoint instrumentation */
 #define TIF_MEMDIE		5	/* is terminating due to OOM killer */
 #define TIF_RESTORE_SIGMASK	6	/* restore signal mask in do_signal() */
 #define TIF_NOTIFY_RESUME	7	/* callback before returning to user */
@@ -115,8 +116,10 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
+#define _TIF_SYSCALL_TRACEPOINT	(1<<TIF_SYSCALL_TRACEPOINT)
 
-#define _TIF_WORK_MASK		(_TIF_SYSCALL_TRACE | _TIF_SINGLESTEP)
+#define _TIF_WORK_MASK		(_TIF_SYSCALL_TRACE | _TIF_SINGLESTEP | \
+				 _TIF_SYSCALL_TRACEPOINT)
 
 /*
  * Thread-synchronous status.

arch/xtensa/include/asm/unistd.h

@@ -22,4 +22,6 @@
 #define __IGNORE_vfork				/* use clone */
 #define __IGNORE_fadvise64			/* use fadvise64_64 */
 
+#define NR_syscalls				__NR_syscalls
+
 #endif /* _XTENSA_UNISTD_H */

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,