[lttng-dev] tracepoint generation is fragile wrt macro expansion

[Mathieu Desnoyers]

* Sébastien Barthélémy (barthelemy at crans.org) wrote:
> Hello,
> 
> please find attached a small patch which demonstrates the problem.
> 
> The patch simply renames the test file ust_tests_hello.h into
> ust_tests-linux-hello.h. The build then fails on linux because the "linux"
> in
> 
>     #define TRACEPOINT_INCLUDE_FILE ./ust_tests-linux-hello.h
> 
> gets expanded to "1", and it then tries to include ust_tests-1-hello.h.

Good point ! Here is the fix:

commit 41858e2b6e81ee5e02eccdd7467b9239d4cdf726
Author: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
Date:   Mon Dec 17 15:36:08 2012 -0500

    Fix: don't do macro expansion in tracepoint file name
    
    Change the API in a backward compatible way: previously, probe headers
    would do e.g.
    
     #define TRACEPOINT_INCLUDE_FILE ./ust_tests-linux-hello.h

    but e.g. "linux" here would be expanded to "1", which is bad.
    
    Fix this by allowing those headers to do:
 
     #define TRACEPOINT_INCLUDE "./ust_tests-linux-hello.h"
   
    instead. We still support the old TRACEPOINT_INCLUDE_FILE for backward
    compatibility.
    
    Reported-by: Sébastien Barthélémy <barthelemy at crans.org>
    Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>

> 
> I do not know if this can be fixed, hopefully you'll have a better idea.
> 
> I came into the problem because I generate the tracepoint definition file
> (à la lttng-gen-tp) but define TRACEPOINT_INCLUDE_FILE to the full path of
> the generated file, which happens to be in the build directory, something
> like .../build-sys-linux-x86_64/..., So I'm more exposed.
> 
> Maybe a possible solution would involve __FILE__?

Nope, unfortunately, __FILE__ always expands to the file in which
__FILE__ is located, not, e.g., the header referring to a macro
containing __FILE__.

Please let me know if the patch above works for you,

Thanks,

Mathieu


> 
> Cheers
> 
> -- Sébastien


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-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com