stacktrace: Handle dladdr function failure

dladdr function could be failed.
There could be only three cases.
Followings are the way to print for each cases.
Consider symbol name as A, symbol offset as B, shared object name as C
and shared object offset as D

Case 1: Success
  A +B (C +D)
Case 2: Failed to get symbol but succeed to get shared object
  (C +D)
Case 3: Failed to get symbol as well as shared object
  unknown

Signed-off-by: Bojun Seo <bojun.seo.0@gmail.com>

src/stacktrace.cc

@@ -95,23 +95,25 @@ static void print_backtrace_symbol(int count, void *addr)
 	char *symbol;
 	int offset;
 	int status;
-
-	// dladdr() translates address to symbolic info.
-	dladdr(addr, &dlip);
+	int dl_ret;
+	int len = SYMBOL_MAXLEN;
 
 #if __SIZEOF_LONG__ == 4
 	pr_out("%2d [%#10lx] ", count, (unsigned long)addr);
 #else
 	pr_out("%2d [%#14lx] ", count, (unsigned long)addr);
 #endif
+	// dladdr() translates address to symbolic info.
+	dl_ret = dladdr(addr, &dlip);
+	if (dl_ret == 0) {
+		pr_out("?\n");
+		return;
+	}
 
-	symbol = abi::__cxa_demangle(dlip.dli_sname, nullptr, nullptr, &status);
-
-	if (status == -2 && !symbol)
-		symbol = strdup(dlip.dli_sname);
-
-	if (symbol) {
-		int len = SYMBOL_MAXLEN;
+	if (dlip.dli_sname != NULL && dlip.dli_saddr != NULL) {
+		symbol = abi::__cxa_demangle(dlip.dli_sname, nullptr, nullptr, &status);
+		if (status != 0)
+			symbol = strdup(dlip.dli_sname);
 
 		if (strlen(symbol) > len) {
 			symbol[len - 3] = '.';