UPDATE Re: making use of userland dtrace on FreeBSD

[Peter Wemm]

On Wed, Dec 26, 2012 at 8:00 PM, Alfred Perlstein <bright at mu.org> wrote:

> 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.

The drawbacks are mostly performance related.  It defeats a certain
hardware optimizations for call/return on leaf functions.  It'll
mostly affect things like math, crypto, compression and multimedia
libraries (that's ffmpeg, bzip2/gzip/libarchive, openssl, etc) but, we
generally don't seem to care about that sort of performance anyway, so
what's one more loss?

Of course it wouldn't be required with dwarf unwinding awareness, but
we don't have that.

We have -fno-omit-frame-pointer on the amd64 kernel whenever debugging
is compiled in because there's no unwinder for doing stack traces.  We
need a dwarf2+ unwinder and somebody to instrument the call frame
state through the remaining assembler code.

-- 
Peter Wemm - peter at wemm.org; peter at FreeBSD.org; peter at yahoo-inc.com; KI6FJV
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"If Java had true garbage collection, most programs would delete
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