perf callchain: Add order support for libunwind DWARF unwinder

As reported by Milian, currently for DWARF unwind (both libdw and
libunwind) we display callchain in callee order only.

Adding the support to follow callchain order setup to libunwind DWARF
unwinder, so we could get following output for report:

$ perf record --call-graph dwarf ls
...
$ perf report --no-children --stdio

39.26% ls libc-2.21.so [.] __strcoll_l
|
---__strcoll_l
mpsort_with_tmp
mpsort_with_tmp
sort_files
main
__libc_start_main
_start
0

$ perf report -g caller --no-children --stdio
...
39.26% ls libc-2.21.so [.] __strcoll_l
|
---0
_start
__libc_start_main
main
sort_files
mpsort_with_tmp
mpsort_with_tmp
__strcoll_l

Based-on-patch-by: Milian Wolff <[e-mail]>
Reported-and-Tested-by: Milian Wolff <[e-mail]>
Signed-off-by: Jiri Olsa <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Tested-by: Wang Nan <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Wang Nan <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/unwind-libunwind.c

···
 		       void *arg, int max_stack)
 {
 	u64 val;
+	unw_word_t ips[max_stack];
 	unw_addr_space_t addr_space;
 	unw_cursor_t c;
-	int ret;
+	int ret, i = 0;
 
 	ret = perf_reg_value(&val, &ui->sample->user_regs, PERF_REG_IP);
 	if (ret)
 		return ret;
 
-	ret = entry(val, ui->thread, cb, arg);
-	if (ret)
-		return -ENOMEM;
+	ips[i++] = (unw_word_t) val;
 
-	if (--max_stack == 0)
-		return 0;
+	/*
+	 * If we need more than one entry, do the DWARF
+	 * unwind itself.
+	 */
+	if (max_stack - 1 > 0) {
+		addr_space = thread__priv(ui->thread);
+		if (addr_space == NULL)
+			return -1;
 
-	addr_space = thread__priv(ui->thread);
-	if (addr_space == NULL)
-		return -1;
+		ret = unw_init_remote(&c, addr_space, ui);
+		if (ret)
+			display_error(ret);
 
-	ret = unw_init_remote(&c, addr_space, ui);
-	if (ret)
-		display_error(ret);
+		while (!ret && (unw_step(&c) > 0) && i < max_stack) {
+			unw_get_reg(&c, UNW_REG_IP, &ips[i]);
+			++i;
+		}
 
-	while (!ret && (unw_step(&c) > 0) && max_stack--) {
-		unw_word_t ip;
+		max_stack = i;
+	}
 
-		unw_get_reg(&c, UNW_REG_IP, &ip);
-		ret = ip ? entry(ip, ui->thread, cb, arg) : 0;
+	/*
+	 * Display what we got based on the order setup.
+	 */
+	for (i = 0; i < max_stack && !ret; i++) {
+		int j = i;
+
+		if (callchain_param.order == ORDER_CALLER)
+			j = max_stack - i - 1;
+		ret = ips[j] ? entry(ips[j], ui->thread, cb, arg) : 0;
 	}
 
 	return ret;