On Fri, 9 Feb 2018 14:13:01 +0900
Namhyung Kim [off-list ref] wrote:

On Fri, Feb 02, 2018 at 06:05:15PM -0500, Steven Rostedt wrote:

quoted

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

Allow the function based events to retrieve not only the parameters offsets,
but also get data from a pointer within a parameter structure. Something
like:

 # echo 'ip_rcv(string skdev+16[0][0] | x8[6] skperm+16[0]+558)' > function_events

 # echo 1 > events/functions/ip_rcv/enable
 # cat trace
    <idle>-0     [003] ..s3   310.626391: __netif_receive_skb_core->ip_rcv(skdev=em1, skperm=b4,b5,2f,ce,18,65)
    <idle>-0     [003] ..s3   310.626400: __netif_receive_skb_core->ip_rcv(skdev=em1, skperm=b4,b5,2f,ce,18,65)
    <idle>-0     [003] ..s3   312.183775: __netif_receive_skb_core->ip_rcv(skdev=em1, skperm=b4,b5,2f,ce,18,65)
    <idle>-0     [003] ..s3   312.184329: __netif_receive_skb_core->ip_rcv(skdev=em1, skperm=b4,b5,2f,ce,18,65)
    <idle>-0     [003] ..s3   312.303895: __netif_receive_skb_core->ip_rcv(skdev=em1, skperm=b4,b5,2f,ce,18,65)
    <idle>-0     [003] ..s3   312.304610: __netif_receive_skb_core->ip_rcv(skdev=em1, skperm=b4,b5,2f,ce,18,65)
    <idle>-0     [003] ..s3   312.471980: __netif_receive_skb_core->ip_rcv(skdev=em1, skperm=b4,b5,2f,ce,18,65)
    <idle>-0     [003] ..s3   312.472908: __netif_receive_skb_core->ip_rcv(skdev=em1, skperm=b4,b5,2f,ce,18,65)
    <idle>-0     [003] ..s3   313.135804: __netif_receive_skb_core->ip_rcv(skdev=em1, skperm=b4,b5,2f,ce,18,65)

That is, we retrieved the net_device of the sk_buff and displayed its name
and perm_addr info.

  sk->dev->name, sk->dev->perm_addr

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---  

[SNIP]

quoted

+static unsigned long process_redirects(struct func_arg *arg, unsigned long val,
+				       char *buf)
+{
+	struct func_arg_redirect *redirect;
+	int ret;
+
+	if (arg->indirect) {
+		ret = probe_kernel_read(buf, (void *)val, sizeof(long));
+		if (ret)
+			return 0;
+		val = *(unsigned long *)buf;
+	}
+
+	list_for_each_entry(redirect, &arg->redirects, list) {
+		val += redirect->index;
+		if (redirect->indirect) {
+			val += (redirect->indirect ^ INDIRECT_FLAG);
+			ret = probe_kernel_read(buf, (void *)val, sizeof(long));
+			if (ret)
+				return 0;
+		}
+	}
+	return val;
+}
+
+static long long __get_arg(struct func_arg *arg, unsigned long long val)
 {
 	char buf[8];
 	int ret;
 
 	val += arg->index;
 
-	if (!arg->indirect)
-		return val;
+	if (arg->indirect)
+		val += (arg->indirect ^ INDIRECT_FLAG);
 
-	val = val + (arg->indirect ^ INDIRECT_FLAG);
+	if (!list_empty(&arg->redirects))
+		val = process_redirects(arg, val, buf);
+
+	if (!val)
+		return 0;
 
 	/* Arrays and strings do their own indirect reads */
-	if (arg->array || arg->func_type == FUNC_TYPE_string)
+	if (!arg->indirect || arg->array || arg->func_type == FUNC_TYPE_string)
 		return val;  

It seems the indirect is processed twice with redirects.  Consider
"x64 foo[0]+4", the process_redirects() will call probe_kernel_read()
and then here again.

Good catch!

It should have been:

		return process_redirects(arg, val, buf);

Thanks!

-- Steve