Re: ehci dynamic debug problem

Alan Stern
2012-04-13T14:36:03Z

On Fri, 13 Apr 2012, Johannes Stezenbach wrote:

> Hi,
>
> I have a quirky device and enabled dynamic debug to
> see the ehci driver debug messages to help me diagnose
> the problem. I see stuff like this:
>
> [1790542.363321] ehci_hub_control:940: ehci_hcd 0000:00:1a.0: \xffffffd8\xffffff94\xffffff94\xffffffa8\xffffff81\xffffffff\xffffffff\xffffffff\xffffffff}[<\xffffff81\xffffffff\xffffffff\xffffffff\xffffffff\x01
> [1790542.363470] ehci_hub_control:940: ehci_hcd 0000:00:1a.0: \xffffffd8\xffffff94\xffffff94\xffffffa8\xffffff81\xffffffff\xffffffff\xffffffff\xffffffff}[<\xffffff81\xffffffff\xffffffff\xffffffff\xffffffff\x01
>
> The problem is in ehci-dbg.c:
>
> #define dbg_port(ehci, label, port, status) { \
> char _buf [80]; \
> dbg_port_buf (_buf, sizeof _buf, label, port, status); \
> ehci_dbg (ehci, "%s\n", _buf); \
> }
>
> dbg_port_buf() is a no op when DEBUG is not defined, thus
> the ehci_dbg() prints uninitialized memory.

Interesting. I have never run across this, because I never use dynamic
debug.

> Does dynamic debug offer an "is the message two lines below enabled" test?
> Simply changing the "#ifdef DEBUG" for dbg_port_buf()
> to "#if defined(DEBUG) || defined(CONFIG_DYNAMIC_DEBUG)"
> is probably not acceptable due to the overhead of dbg_port_buf()?

I don't understand your question. Doesn't dbg_port_buf need to be
defined whenever dynamic debugging is enabled?

Alternatively, the definition of dbg_port_buf (and related routines) in
the !defined(DEBUG) case could be changed; you could add

buf[0] = 0;

That way you wouldn't get garbage out, although you wouldn't get
anything useful either.

Alan Stern