[PATCH v5 6/6] arm64: ftrace: add a test of function prologue analyzer

[AKASHI Takahiro]

The patch ("arm64: ftrace: add arch-specific stack tracer") introduced
a function prologue analyzer.

Given that there is no fixed template for a function prologue, at least
on gcc for aarch64, a function prologue analyzer may be rather heuristic.
So this patch adds a kernel command line option,
function_prologue_analyzer_test, in order to run a basic test at startup
by executing an analyzer against all the *traceable* functions.

For function_prologue_analyzer_test=2, the output looks like:

       po sp    fp    symbol
       == ==    ==    ======
    0: 0  0x040 0x000 gic_handle_irq+0x20/0xa4
    1: 0  0x040 0x000 gic_handle_irq+0x34/0x114
    2: 0  0x030 0x000 run_init_process+0x14/0x48
    3: 0  0x020 0x000 try_to_run_init_process+0x14/0x58
    4: 0  0x080 0x000 do_one_initcall+0x1c/0x194
    ...
22959: 0  0x020 0x000 tty_lock_slave+0x14/0x3c
22960: 0  0x020 0x000 tty_unlock_slave+0x14/0x3c
function prologue analyzer test: 0 errors

"po" indicates a position of callsite of mcount(), and should be zero
if an analyzer has parsed a function prologue successfully and reached
a location where fp is properly updated.
"sp" is a final offset to a parent's fp at the exit of function prologue.
"fp" is also an ofset against sp at the exit of function prologue.
So normally,
  <new sp> = <old fp> + <"sp">
  <new fp> = <new sp> - <"fp">

And the last line shows the number of possible errors in the result.

For function_prologue_analyzer_test=1, only the last line will be shown.

Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
---
 arch/arm64/kernel/stacktrace.c |   52 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
index 4ee052a..d1a9e5b 100644
--- a/arch/arm64/kernel/stacktrace.c
+++ b/arch/arm64/kernel/stacktrace.c
@@ -18,6 +18,7 @@
 #include <linux/kernel.h>
 #include <linux/export.h>
 #include <linux/ftrace.h>
+#include <linux/kallsyms.h>
 #include <linux/sched.h>
 #include <linux/stacktrace.h>
 
@@ -322,5 +323,56 @@ void save_stack_trace_sp(struct stack_trace *trace,
 {
 	__save_stack_trace_tsk(current, trace, stack_dump_sp);
 }
+
+static int start_analyzer_test __initdata;
+
+static int __init enable_analyzer_test(char *str)
+{
+	get_option(&str, &start_analyzer_test);
+	return 0;
+}
+early_param("function_prologue_analyzer_test", enable_analyzer_test);
+
+static void __init do_test_function_prologue_analyzer(void)
+{
+	extern unsigned long __start_mcount_loc[];
+	extern unsigned long __stop_mcount_loc[];
+	unsigned long count, i, errors;
+	int print_once;
+
+	count = __stop_mcount_loc - __start_mcount_loc;
+	errors = print_once = 0;
+	for (i = 0; i < count; i++) {
+		unsigned long addr, sp_off, fp_off;
+		int pos;
+		bool check;
+		char buf[60];
+
+		addr = __start_mcount_loc[i];
+		pos = analyze_function_prologue(addr, &sp_off, &fp_off);
+		check = ((pos != 0) || !sp_off || (sp_off <= fp_off));
+		if (check)
+			errors++;
+		if (check || (start_analyzer_test > 1)) {
+			if (!print_once) {
+				pr_debug("       po sp    fp    symbol\n");
+				pr_debug("       == ==    ==    ======\n");
+				print_once++;
+			}
+			sprint_symbol(buf, addr);
+			pr_debug("%5ld: %d  0x%03lx 0x%03lx %s\n",
+					i, pos, sp_off, fp_off, buf);
+		}
+	}
+	pr_debug("function prologue analyzer test: %ld errors\n", errors);
+}
+
+static int __init test_function_prologue_analyzer(void)
+{
+	if (start_analyzer_test)
+		do_test_function_prologue_analyzer();
+	return 0;
+}
+late_initcall(test_function_prologue_analyzer);
 #endif /* CONFIG_STACK_TRACER */
 #endif
-- 
1.7.9.5