[PATCH v3] tracing: Function stack size and its name mismatch in arm64

[Jiping Ma]

There is not PC in ARM64 stack, LR is used to for walk_stackframe in
ARM64. Tere is no the issue in ARM32 because there is PC in ARM32 stack.
PC is used to calculate the stack size in trace_stack.c, so the
function name and its stack size appear to be off-by-one.
ARM64 stack layout:
	LR
        FP
        ......
        LR
        FP
        ......

Wrong info:
Depth Size Location (16 entries)
----- ---- --------
0) 5400 16 __update_load_avg_se.isra.2+0x28/0x220
1) 5384 96 put_prev_entity+0x250/0x338
2) 5288 80 pick_next_task_fair+0x4c4/0x508
3) 5208 72 __schedule+0x100/0x600
4) 5136 184 preempt_schedule_common+0x28/0x48
5) 4952 32 preempt_schedule+0x28/0x30
6) 4920 16 vprintk_emit+0x170/0x1f8
7) 4904 128 vprintk_default+0x48/0x58
8) 4776 64 vprintk_func+0xf8/0x1c8
9) 4712 112 printk+0x70/0x90
10) 4600 176 occupy_stack_init+0x64/0xc0 [kernel_stack]
11) 4424 3376 do_one_initcall+0x68/0x248
12) 1048 144 do_init_module+0x60/0x1f0
13) 904 48 load_module+0x1d50/0x2340
14) 856 352 sys_finit_module+0xd0/0xe8
15) 504 504 el0_svc_naked+0x30/0x34

Correct info:
Depth Size Location (18 entries)
----- ---- --------
0) 5464 48 cgroup_rstat_updated+0x20/0x100
1) 5416 32 cgroup_base_stat_cputime_account_end.isra.0+0x30/0x60
2) 5384 32 __cgroup_account_cputime+0x3c/0x48
3) 5352 64 update_curr+0xc4/0x1d0
4) 5288 72 pick_next_task_fair+0x444/0x508
5) 5216 184 __schedule+0x100/0x600
6) 5032 32 preempt_schedule_common+0x28/0x48
7) 5000 16 preempt_schedule+0x28/0x30
8) 4984 128 vprintk_emit+0x170/0x1f8
9) 4856 64 vprintk_default+0x48/0x58
10) 4792 112 vprintk_func+0xf8/0x1c8
11) 4680 176 printk+0x70/0x90
12) 4504 80 func_test+0x7c/0xb8 [kernel_stack]
13) 4424 3376 occupy_stack_init+0x7c/0xc0 [kernel_stack]
14) 1048 144 do_one_initcall+0x68/0x248
15) 904 48 do_init_module+0x60/0x1f0
16) 856 352 load_module+0x1d50/0x2340
17) 504 504 sys_finit_module+0xd0/0xe8

Signed-off-by: Jiping Ma <jiping.ma2@xxxxxxxxxxxxx>
---
 kernel/trace/trace_stack.c | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_stack.c b/kernel/trace/trace_stack.c
index 5d16f73898db..ed80b95abf06 100644
--- a/kernel/trace/trace_stack.c
+++ b/kernel/trace/trace_stack.c
@@ -40,16 +40,28 @@ static void print_max_stack(void)
 
 	pr_emerg("        Depth    Size   Location    (%d entries)\n"
 			   "        -----    ----   --------\n",
+#ifdef CONFIG_ARM64
+			   stack_trace_nr_entries - 1);
+#else
 			   stack_trace_nr_entries);
-
+#endif
+#ifdef CONFIG_ARM64
+	for (i = 1; i < stack_trace_nr_entries; i++) {
+#else
 	for (i = 0; i < stack_trace_nr_entries; i++) {
+#endif
 		if (i + 1 == stack_trace_nr_entries)
 			size = stack_trace_index[i];
 		else
 			size = stack_trace_index[i] - stack_trace_index[i+1];
 
+#ifdef CONFIG_ARM64
+		pr_emerg("%3ld) %8d   %5d   %pS\n", i-1, stack_trace_index[i],
+				size, (void *)stack_dump_trace[i-1]);
+#else
 		pr_emerg("%3ld) %8d   %5d   %pS\n", i, stack_trace_index[i],
 				size, (void *)stack_dump_trace[i]);
+#endif
 	}
 }
 
@@ -324,8 +336,11 @@ static int t_show(struct seq_file *m, void *v)
 		seq_printf(m, "        Depth    Size   Location"
 			   "    (%d entries)\n"
 			   "        -----    ----   --------\n",
+#ifdef CONFIG_ARM64
+			   stack_trace_nr_entries - 1);
+#else
 			   stack_trace_nr_entries);
-
+#endif
 		if (!stack_tracer_enabled && !stack_trace_max_size)
 			print_disabled(m);
 
@@ -334,6 +349,10 @@ static int t_show(struct seq_file *m, void *v)
 
 	i = *(long *)v;
 
+#ifdef CONFIG_ARM64
+	if (i == 0)
+		return 0;
+#endif
 	if (i >= stack_trace_nr_entries)
 		return 0;
 
@@ -342,9 +361,14 @@ static int t_show(struct seq_file *m, void *v)
 	else
 		size = stack_trace_index[i] - stack_trace_index[i+1];
 
+#ifdef CONFIG_ARM64
+	seq_printf(m, "%3ld) %8d   %5d   ", i-1, stack_trace_index[i], size);
+	trace_lookup_stack(m, i-1);
+#else
 	seq_printf(m, "%3ld) %8d   %5d   ", i, stack_trace_index[i], size);
 
 	trace_lookup_stack(m, i);
+#endif
 
 	return 0;
 }
-- 
2.18.1