[PATCH v2] arm64: ftrace: Fix to enable syscall events on arm64

[Masami Hiramatsu]

Since commit 4378a7d4be30 ("arm64: implement syscall wrappers")
introduced "__arm64_" prefix to all syscall wrapper symbols in
sys_call_table, syscall tracer can not find corresponding
metadata from syscall name. In the result, we have no syscall
ftrace events on arm64 kernel, and some bpf testcases are failed
on arm64.

To fix this issue, this introduces custom
arch_syscall_match_sym_name() which skips first 8 bytes when
comparing the syscall and symbol names.

Fixes: 4378a7d4be30 ("arm64: implement syscall wrappers")
Reported-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Acked-by: Will Deacon <will.deacon@xxxxxxx>
Tested-by: Naresh Kamboju <naresh.kamboju@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
 arch/arm64/include/asm/ftrace.h |   13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index caa955f10e19..fac54fb050d0 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -56,6 +56,19 @@ static inline bool arch_trace_is_compat_syscall(struct pt_regs *regs)
 {
 	return is_compat_task();
 }
+
+#define ARCH_HAS_SYSCALL_MATCH_SYM_NAME
+
+static inline bool arch_syscall_match_sym_name(const char *sym,
+					       const char *name)
+{
+	/*
+	 * Since all syscall functions have __arm64_ prefix, we must skip it.
+	 * However, as we described above, we decided to ignore compat
+	 * syscalls, so we don't care about __arm64_compat_ prefix here.
+	 */
+	return !strcmp(sym + 8, name);
+}
 #endif /* ifndef __ASSEMBLY__ */
 
 #endif /* __ASM_FTRACE_H */