[PATCH] stacktrace: print real address of trace entries

[PATCH] stacktrace: print real address of trace entries

[Haesung Kim]

If function is marked as static and compiler decies to lnline function
with or without inline keyword, the function has no symbol.
We just know symbol located near the address of the inline function
by %pS type that shows symbol and offset. But we don't know function
name.
The real address let us extract the function name and location of
source code by debugging tools such as addr2line. This is helpful to
debug.

Signed-off-by: Haesung Kim <matia.kim@lge.com>
---
 kernel/stacktrace.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
index 946f44a..b7168c5 100644
--- a/kernel/stacktrace.c
+++ b/kernel/stacktrace.c
@@ -24,12 +24,15 @@ void stack_trace_print(const unsigned long *entries, unsigned int nr_entries,
 		       int spaces)
 {
 	unsigned int i;
+	unsigned long ip;
 
 	if (WARN_ON(!entries))
 		return;
 
 	for (i = 0; i < nr_entries; i++)
-		printk("%*c%pS\n", 1 + spaces, ' ', (void *)entries[i]);
+		ip = entries[i];
+		printk("%*c[<%px>] %pS\n",
+			1 + spaces, ' ', (void *) ip, (void *) ip);
 }
 EXPORT_SYMBOL_GPL(stack_trace_print);
 
@@ -47,13 +50,15 @@ int stack_trace_snprint(char *buf, size_t size, const unsigned long *entries,
 			unsigned int nr_entries, int spaces)
 {
 	unsigned int generated, i, total = 0;
+	unsigned long ip;
 
 	if (WARN_ON(!entries))
 		return 0;
 
 	for (i = 0; i < nr_entries && size; i++) {
-		generated = snprintf(buf, size, "%*c%pS\n", 1 + spaces, ' ',
-				     (void *)entries[i]);
+		ip = entries[i];
+		generated = snprintf(buf, size, "%*c[<%px>] %pS\n",
+				     1 + spaces, ' ', (void *) ip, (void *) ip);
 
 		total += generated;
 		if (generated >= size) {
-- 
2.7.4

Re: [PATCH] stacktrace: print real address of trace entries

[Mark Rutland]

On Fri, Sep 04, 2020 at 07:00:24PM +0900, Haesung Kim wrote:
> If function is marked as static and compiler decies to lnline function
> with or without inline keyword, the function has no symbol.
> We just know symbol located near the address of the inline function
> by %pS type that shows symbol and offset. But we don't know function
> name.

What exactly is output in this case today? Can't you get the real
addr/symbol from scripts/faddr2line?

> The real address let us extract the function name and location of
> source code by debugging tools such as addr2line. This is helpful to
> debug.

Not logging the address was a deliberate decision to minimize leakage of
the kernel's VA layout. This undermines that, and I don't think doing so
is a good idea.

If there is a problem with faddr2line we should work out how to improve
that.

Mark.

> 
> Signed-off-by: Haesung Kim <matia.kim@lge.com>
> ---
>  kernel/stacktrace.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c
> index 946f44a..b7168c5 100644
> --- a/kernel/stacktrace.c
> +++ b/kernel/stacktrace.c
> @@ -24,12 +24,15 @@ void stack_trace_print(const unsigned long *entries, unsigned int nr_entries,
>  		       int spaces)
>  {
>  	unsigned int i;
> +	unsigned long ip;
>  
>  	if (WARN_ON(!entries))
>  		return;
>  
>  	for (i = 0; i < nr_entries; i++)
> -		printk("%*c%pS\n", 1 + spaces, ' ', (void *)entries[i]);
> +		ip = entries[i];
> +		printk("%*c[<%px>] %pS\n",
> +			1 + spaces, ' ', (void *) ip, (void *) ip);
>  }
>  EXPORT_SYMBOL_GPL(stack_trace_print);
>  
> @@ -47,13 +50,15 @@ int stack_trace_snprint(char *buf, size_t size, const unsigned long *entries,
>  			unsigned int nr_entries, int spaces)
>  {
>  	unsigned int generated, i, total = 0;
> +	unsigned long ip;
>  
>  	if (WARN_ON(!entries))
>  		return 0;
>  
>  	for (i = 0; i < nr_entries && size; i++) {
> -		generated = snprintf(buf, size, "%*c%pS\n", 1 + spaces, ' ',
> -				     (void *)entries[i]);
> +		ip = entries[i];
> +		generated = snprintf(buf, size, "%*c[<%px>] %pS\n",
> +				     1 + spaces, ' ', (void *) ip, (void *) ip);
>  
>  		total += generated;
>  		if (generated >= size) {
> -- 
> 2.7.4
>