perf session: Fix Intel LBR callstack entries and nr print message

When generating callstack information from branch_stack(Intel LBR), the
actual number of callstack entry should be bigger than the number of
branch_stack, for example:

branch_stack records:
B() -> C()
A() -> B()
converted callstack records should be:
C()
B()
A()
though, the number of callstack equals
to the number of branch stack plus 1.

This patch fixes above issue in branch_stack__printf(). For example,

# echo 'scale=2000; 4*a(1)' > cmd
# perf record --call-graph lbr bc -l < cmd

Before applying this patch, `perf script -D` output:

1220022677386876 0x2a40 [0xd8]: PERF_RECORD_SAMPLE(IP, 0x4002): 17990/17990: 0x40a6d6 period: 894172 addr: 0
... LBR call chain: nr:8
..... 0: fffffffffffffe00
..... 1: 000000000040a410
..... 2: 000000000040573c
..... 3: 0000000000408650
..... 4: 00000000004022f2
..... 5: 00000000004015f5
..... 6: 00007f5ed6dcb553
..... 7: 0000000000401698
... FP chain: nr:2
..... 0: fffffffffffffe00
..... 1: 000000000040a6d8
... branch callstack: nr:6 # which is not consistent with LBR records.
..... 0: 000000000040a410
..... 1: 0000000000408650 # ditto
..... 2: 00000000004022f2
..... 3: 00000000004015f5
..... 4: 00007f5ed6dcb553
..... 5: 0000000000401698
... thread: bc:17990
...... dso: /usr/bin/bc
bc 17990 1220022.677386: 894172 cycles:
40a410 [unknown] (/usr/bin/bc)
40573c [unknown] (/usr/bin/bc)
408650 [unknown] (/usr/bin/bc)
4022f2 [unknown] (/usr/bin/bc)
4015f5 [unknown] (/usr/bin/bc)
7f5ed6dcb553 __libc_start_main+0xf3 (/usr/lib64/libc-2.17.so)
401698 [unknown] (/usr/bin/bc)

After applied:

1220022677386876 0x2a40 [0xd8]: PERF_RECORD_SAMPLE(IP, 0x4002): 17990/17990: 0x40a6d6 period: 894172 addr: 0
... LBR call chain: nr:8
..... 0: fffffffffffffe00
..... 1: 000000000040a410
..... 2: 000000000040573c
..... 3: 0000000000408650
..... 4: 00000000004022f2
..... 5: 00000000004015f5
..... 6: 00007f5ed6dcb553
..... 7: 0000000000401698
... FP chain: nr:2
..... 0: fffffffffffffe00
..... 1: 000000000040a6d8
... branch callstack: nr:7
..... 0: 000000000040a410
..... 1: 000000000040573c
..... 2: 0000000000408650
..... 3: 00000000004022f2
..... 4: 00000000004015f5
..... 5: 00007f5ed6dcb553
..... 6: 0000000000401698
... thread: bc:17990
...... dso: /usr/bin/bc
bc 17990 1220022.677386: 894172 cycles:
40a410 [unknown] (/usr/bin/bc)
40573c [unknown] (/usr/bin/bc)
408650 [unknown] (/usr/bin/bc)
4022f2 [unknown] (/usr/bin/bc)
4015f5 [unknown] (/usr/bin/bc)
7f5ed6dcb553 __libc_start_main+0xf3 (/usr/lib64/libc-2.17.so)
401698 [unknown] (/usr/bin/bc)

Change from v1:
- refined code style according to Jiri's review comments.

Signed-off-by: Chengdong Li <[e-mail]>
Acked-by: Namhyung Kim <[e-mail]>
Cc: Adrian Hunter <[e-mail]>
Cc: Alexander Shishkin <[e-mail]>
Cc: Alexey Bayduraev <[e-mail]>
Cc: Andi Kleen <[e-mail]>
Cc: German Gomez <[e-mail]>
Cc: Ian Rogers <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Mark Rutland <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Riccardo Mancini <[e-mail]>
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/session.c

···
 	struct branch_entry *entries = perf_sample__branch_entries(sample);
 	uint64_t i;
 
-	printf("%s: nr:%" PRIu64 "\n",
-		!callstack ? "... branch stack" : "... branch callstack",
-		sample->branch_stack->nr);
+	if (!callstack) {
+		printf("%s: nr:%" PRIu64 "\n", "... branch stack", sample->branch_stack->nr);
+	} else {
+		/* the reason of adding 1 to nr is because after expanding
+		 * branch stack it generates nr + 1 callstack records. e.g.,
+		 *         B()->C()
+		 *         A()->B()
+		 * the final callstack should be:
+		 *         C()
+		 *         B()
+		 *         A()
+		 */
+		printf("%s: nr:%" PRIu64 "\n", "... branch callstack", sample->branch_stack->nr+1);
+	}
 
 	for (i = 0; i < sample->branch_stack->nr; i++) {
 		struct branch_entry *e = &entries[i];
···
 				(unsigned)e->flags.reserved,
 				e->flags.type ? branch_type_name(e->flags.type) : "");
 		} else {
-			printf("..... %2"PRIu64": %016" PRIx64 "\n",
-				i, i > 0 ? e->from : e->to);
+			if (i == 0) {
+				printf("..... %2"PRIu64": %016" PRIx64 "\n"
+				       "..... %2"PRIu64": %016" PRIx64 "\n",
+						i, e->to, i+1, e->from);
+			} else {
+				printf("..... %2"PRIu64": %016" PRIx64 "\n", i+1, e->from);
+			}
 		}
 	}
 }