This patch allows system call entry or exit to be traced as ftrace events,
ie. sys_enter_*/sys_exit_*, if CONFIG_FTRACE_SYSCALLS is enabled.
Those events appear and can be controlled under
    ${sysfs}/tracing/events/syscalls/

Please note that we can't trace compat system calls here because
AArch32 mode does not share the same syscall table with AArch64.
Just define ARCH_TRACE_IGNORE_COMPAT_SYSCALLS in order to avoid unexpected
results (bogus syscalls reported or even hang-up).

Signed-off-by: AKASHI Takahiro <redacted>
---
 arch/arm64/Kconfig               |    1 +
 arch/arm64/include/asm/ftrace.h  |   20 ++++++++++++++++
 arch/arm64/include/asm/syscall.h |    1 +
 arch/arm64/include/asm/unistd.h  |    2 ++
 arch/arm64/kernel/ptrace.c       |   48 ++++++++++++++++++++++----------------
 5 files changed, 52 insertions(+), 20 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 6954959..b1dcdb4 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig

@@ -43,6 +43,7 @@ config ARM64
 	select HAVE_MEMBLOCK
 	select HAVE_PATA_PLATFORM
 	select HAVE_PERF_EVENTS
+	select HAVE_SYSCALL_TRACEPOINTS
 	select IRQ_DOMAIN
 	select MODULES_USE_ELF_RELA
 	select NO_BOOTMEM

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index c44c4b1..4ef06f1 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h

@@ -44,6 +44,26 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
 #define CALLER_ADDR4 ((unsigned long)return_address(4))
 #define CALLER_ADDR5 ((unsigned long)return_address(5))
 #define CALLER_ADDR6 ((unsigned long)return_address(6))
+
+#include <asm/compat.h>
+
+/*
+ * Because AArch32 mode does not share the same syscall table with AArch64,
+ * tracing compat syscalls may result in reporting bogus syscalls or even
+ * hang-up, so just do not trace them.
+ * See kernel/trace/trace_syscalls.c
+ *
+ * x86 code says:
+ * If the user realy wants these, then they should use the
+ * raw syscall tracepoints with filtering.

 #endif /* ifndef __ASSEMBLY__ */
 
 #endif /* __ASM_FTRACE_H */

diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
index 70ba9d4..383771e 100644
--- a/arch/arm64/include/asm/syscall.h
+++ b/arch/arm64/include/asm/syscall.h

@@ -18,6 +18,7 @@
 
 #include <linux/err.h>
 
+extern const void *sys_call_table[];
 
 static inline int syscall_get_nr(struct task_struct *task,
 				 struct pt_regs *regs)

diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
index 82ce217..c335479 100644
--- a/arch/arm64/include/asm/unistd.h
+++ b/arch/arm64/include/asm/unistd.h

@@ -28,3 +28,5 @@
 #endif
 #define __ARCH_WANT_SYS_CLONE
 #include <uapi/asm/unistd.h>
+
+#define NR_syscalls (__NR_syscalls)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 9993a8f..9c52b3e 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c

@@ -41,6 +41,9 @@
 #include <asm/traps.h>
 #include <asm/system_misc.h>
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/syscalls.h>
+
 /*
  * TODO: does not yet catch signals sent when the child dies.
  * in exit.c or in signal.c.

@@ -1062,29 +1065,31 @@ asmlinkage int syscall_trace_enter(struct pt_regs *regs)
 {
 	unsigned long saved_reg;
 
-	if (!test_thread_flag(TIF_SYSCALL_TRACE))
-		return regs->syscallno;
+	if (test_thread_flag(TIF_SYSCALL_TRACE)) {
+		/*
+		 * A scrach register (ip(r12) on AArch32, x7 on AArch64) is
+		 * used to denote syscall entry/exit:
+		 *   0 -> entry
+		 */
+		if (is_compat_task()) {