UPDATE Re: making use of userland dtrace on FreeBSD

[Alfred Perlstein]

Putting the following into /etc/src.conf builds a world that is userland 
dtrace'able:

> /usr/home/alfred # cat /etc/src.conf
> WITH_CTF=1
> CFLAGS+=-fno-omit-frame-pointer
> STRIP=

(yes, STRIP is intentionally left blank)

The following the wiki, just doing this:

> # kldload dtraceall
Then you can test it by doing this:

> # dtruss -s ls |& head -20
If you get stack traces along with syscalls, you're doing pretty well.

Can any of our build gurus look at this?

What would be the drawbacks?  I don't want to hurt freebsd for heavy 
performance, but I think this functionality should work out of the box 
for most people.  It allows an expert to diagnose some pretty gnarly bugs.

My preliminary thoughts are:
   hack gcc to turn off -fomit-frame-pointer unless -O3 or greater is 
specified.
   turn on WITH_CTF in the Mk files or top level Makefiles.
   turn off stripping by default.

What other options are there?  Is there a better way that is expedient?  
I really do not think we should wait for codes to optimize this unless 
the code is hiding somewhere on a branch and ready to commit unless 
there is a strong reason.

Can someone list some strong reasons not to?  Or give encouragement to 
go this way?

-Alfred






On 12/21/12 9:35 AM, Alfred Perlstein wrote:
> Hey folks,
>
> We have had userland dtrace for a while now.  However it's not really 
> hooked up into the build, nor as far as I can tell are ports nor 
> shared libs.
>
> Dtrace can be immensely useful for tracking down hard to find bugs, 
> memory leaks, performance problems and a lot more.
>
> What are the thoughts on making this available by default on FreeBSD 
> going forward?
>
> What would need to happen?
>
> Supposedly we can do this by just adding 
> "CFLAGS=-fno-omit-frame-pointer" and not completely stripping 
> installed tools/libraries.
>
> Would it make sense to set this as default for the whole system? Just 
> libs+ports?  Or do people think that the performance gain of 
> omit-frame-pointer (which I am unsure of) is worth the loss of 
> debug-ability (like a certain arctic bird based OS)?
>
> I have also factored in the size of binaries into this, and I really 
> am not sure why it would be a problem other than if we didn't offer an 
> "easy button" to make things "small".
>
> Let's figure this out, because it seems to me that we should be 
> offering this to our users if possible.
>
> -Alfred
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