[lttng-dev] TRACEPOINT_PROVIDER mismatch check in ust-tracepoint-event.h needs -Wsystem-headers

[David OShea]

Hi Mathieu,

Thanks for the response and apologies for the delay in mine, please see below:

> -----Original Message-----
> From: Mathieu Desnoyers [mailto:mathieu.desnoyers at efficios.com]
> Sent: Tuesday, 20 November 2012 2:56 AM
> To: David OShea
> Cc: lttng-dev at lists.lttng.org
> Subject: Re: [lttng-dev] TRACEPOINT_PROVIDER mismatch check in ust-
> tracepoint-event.h needs -Wsystem-headers
[...]
> > I'm not sure if there is any way you could "fix" this so that
> > -Wsystem-headers isn't required, but perhaps it would at least be
> > worth documenting that this flag could be used - but perhaps not
> > recommend it - to enable those checks to occur.
> 
> I have not found any way to show those warnings from UST system headers
> without -Wsystem-headers. We have the following scenario:
> 
> probe C file
>   -> includes ust probe description file
>      -> includes tracepoint-event.h (system header)
>         -> includes ust probe description file
>         -> includes ust-tracepoint-event.h (system header) [1]
>            For each stage:
>              -> undef/define macros
>              -> includes ust probe description file
> 
> Since the actual functions are created by the compiler in the scope of
> ust-tracepoint-event.h [1] (a system header), the warnings are
> inhibited
> unless we specify -Wsystem-headers.
[...]
> So I guess documenting this would be the right way to do it, unless
> anyone has a better idea ?

I don't know much about the macros in ust-tracepoint-event.h, so this might not make any sense, but could you have the __tracepoint_provider_check_##TRACEPOINT_PROVIDER() function actually get called from the __lttng_events_init__##TRACEPOINT_PROVIDER() (constructor) function?  I assume this would mean you'd get link-time errors if you have a provider name mismatch.  It would also mean a lot of useless calls to empty functions at startup, but I assume that really shouldn't take too long.  Perhaps this checking could be a compile-time option, so that if you're concerned about the startup time impact you can disable it, or perhaps the functions could be marked as inline?

Thanks,
David

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