dtrace discuss - Sep 2007 - Smart pointers causing name mangling problems with wrapped USDT probes in Mozilla

Hi,

We are just in the middle of writing USDT probes for mozilla to allow us 
to trace URI loads and Image loads.

If you just put in a custom probe in a C++ func the function name for 
the probe will come out as the mangled C++ func name. To get around this 
we put the probes into extern "C" wrapper funcs which we then put in
the
code. So far so good.

What we saw though was when we put the wrapper funcs in sometimes we 
still got a probe with the mangled func name and the one we wanted with 
the simple wrapper func name:

bash-3.00$ dtrace -ln "moz*:::"
   ID   PROVIDER            MODULE                          FUNCTION NAME
 5795 mozilla9865         libxul.so 
__1cJimgLoaderJLoadImage6MpnGnsIURI_22pnMnsILoadGroup_pnTimgIDecoderObserver_pnLnsISupports_I8pnLimgIRequest_p9B_I_
load-image-start
 5796 mozilla9865         libxul.so        mozdtrace_load_image_start 
load-image-start
 
Tracking this down we found that if we put the wrapper in the C++ func 
after the declaration of a C++ smart pointer we had no problem. If we 
put it before we saw the above behavior. Looking at the preprocessor 
output in both instances they look the same, apart from being moved 
above or after the smart pointer.

Anyone any ideas? Is this a problem with dtrace -G ?

JR

mozilla/modules/libpr0n/src/

imgLoader.h
------------------
extern "C" {
void mozdtrace_load_image_start(imgIRequest *aRequest, nsIURI *aURI);
}

#define TRACE_MOZILLA_LOAD_IMAGE_START_POINT(aRequest_, aURI_) \
  mozdtrace_load_image_start((aRequest_), (aURI_))

imgLoader.cpp
--------------------
Problem:
NS_IMETHODIMP imgLoader::LoadImage(nsIURI *aURI, ...){
    :
  TRACE_MOZILLA_LOAD_IMAGE_START_POINT(aRequest, aURI);
  nsCOMPtr<nsICacheEntryDescriptor> entry;
    :
}
   
No Problem:
NS_IMETHODIMP imgLoader::LoadImage(nsIURI *aURI, ...){
    :
  nsCOMPtr<nsICacheEntryDescriptor> entry;
  TRACE_MOZILLA_LOAD_IMAGE_START_POINT((aRequest, aURI);
    :
}

imgLoader.cpp
--------------------
void mozdtrace_load_image_start(imgIRequest *aRequest, nsIURI *aURI)
{
    if (MOZILLA_LOAD_IMAGE_START_ENABLED()) { 
        nsCAutoString spec;
       
        aURI->GetAsciiSpec(spec);
        MOZILLA_LOAD_IMAGE_START((int *) aRequest, (char *)spec.get());
    }
}


mozilla-trace.h
---------------------
    :
#ifdef INCLUDE_MOZILLA_DTRACE
    :
#define    MOZILLA_LOAD_IMAGE_START(arg0, arg1) \
    __dtrace_mozilla___load__image__start(arg0, arg1)
#define    MOZILLA_LOAD_IMAGE_START_ENABLED() \
    __dtraceenabled_mozilla___load__image__start()
    :

extern void __dtrace_mozilla___load__image__start(int *, char *);
extern int __dtraceenabled_mozilla___load__image__start(void);
    :

mozilla-trace.d
-------------------
provider mozilla {
    :
 probe load__image__start(int *, char *);
 probe load__image__done(int *, char *);
};