riscv: Fix ftrace syscall handling which are now prefixed with __riscv_

ftrace creates entries for each syscall in the tracefs but has failed
since commit 08d0ce3 ("riscv: Implement syscall wrappers") which
prefixes all riscv syscalls with __riscv_.

So fix this by implementing arch_syscall_match_sym_name() which allows us
to ignore this prefix.

And also ignore compat syscalls like x86/arm64 by implementing
arch_trace_is_compat_syscall().

Fixes: 08d0ce3 ("riscv: Implement syscall wrappers")
Signed-off-by: Alexandre Ghiti <[email protected]>
Reviewed-by: Sami Tolvanen <[email protected]>
Acked-by: Masami Hiramatsu (Google) <[email protected]>
Tested-by: Björn Töpel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Cc: [email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>

arch/riscv/include/asm/ftrace.h

@@ -31,6 +31,27 @@ static inline unsigned long ftrace_call_adjust(unsigned long addr)
 	return addr;
 }
 
+/*
+ * Let's do like x86/arm64 and ignore the compat syscalls.
+ */
+#define ARCH_TRACE_IGNORE_COMPAT_SYSCALLS
+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 __riscv_ prefix, we must skip it.
+	 * However, as we described above, we decided to ignore compat
+	 * syscalls, so we don't care about __riscv_compat_ prefix here.
+	 */
+	return !strcmp(sym + 8, name);
+}
+
 struct dyn_arch_ftrace {
 };
 #endif