Re: [PATCH 1/4] tracing: add error_report trace points

On Thu, 14 Jan 2021 at 08:50, Alexander Potapenko [off-list ref] wrote:

On Wed, Jan 13, 2021 at 10:10 PM Steven Rostedt [off-list ref] wrote:

quoted

On Wed, 13 Jan 2021 10:16:54 +0100
Alexander Potapenko [off-list ref] wrote:

quoted

+DECLARE_EVENT_CLASS(error_report_template,
+                 TP_PROTO(const char *error_detector, unsigned long id),

Instead of having a random string, as this should be used by a small finite
set of subsystems, why not make the above into an enum?

You're probably right.
I just thought it might be a good idea to minimize the effort needed
from tools' authors to add these tracepoints to the tools (see the
following two patches), and leave room for some extensibility (e.g.
passing bug type together with the tool name etc.)

quoted

quoted

+                 TP_ARGS(error_detector, id),
+                 TP_STRUCT__entry(__field(const char *, error_detector)
+                                          __field(unsigned long, id)),
+                 TP_fast_assign(__entry->error_detector = error_detector;
+                                __entry->id = id;),
+                 TP_printk("[%s] %lx", __entry->error_detector,

Then the [%s] portion of this could also be just a __print_symbolic().

We'll need to explicitly list the enum values once again in
__print_symbolic(), right? E.g.:

enum debugging_tool {

We need to use TRACE_DEFINE_ENUM().

         TOOL_KFENCE,

For consistency I would call the enum simply "ERROR_DETECTOR" as well.
(Hypothetically, there could also be an "error detector" that is not a
"debugging tool".)

         TOOL_KASAN,
         ...
}

TP_printk(__print_symbolic(__entry->error_detector, TOOL_KFENCE,
TOOL_KASAN, ...),

It takes a list of val -> str. E.g.
__print_symbolic(__entry->error_detector, { TOOL_KFENCE, "KFENCE" }, {
TOOL_KASAN, "KASAN" }).

Looking around the kernel, sometimes this is simplified with macros,
but not sure if it's worth it. Typing the same thing 3 times is fine,
given this list won't grow really fast.

Thanks,
-- Marco