Re: wiki page on using stap without dwarf

["Frank Ch. Eigler" <fche at redhat dot com>]

Hi -

On Mon, May 19, 2008 at 04:35:39PM -0700, Jim Keniston wrote:
> > Thanks.  One question re. usage: when would one want to use the
> > "--kelf" option?
> 
> --kelf has the following implications:
> 1. It affects whether/how we report the absence of dwarf info.
> 2. It brings into consideration functions that are in the symbol table
> but not the dwarf info -- typically assembly-language functions.

That doesn't seem to answer the question in a way that a systemtap
user would understand.  When should they use --kelf?


> [...]  That said, your suggestion of ~1 month ago -- that we consult
> the dwarf only if the elf doesn't provide what we need, and thereby
> save some cycles in stap -- has merit.  I'll open an enhancement
> request for that, unless you've changed your mind about it.

It still sounds like it should be a win.  (One problem - shared by all
the symbol-table sources - is relocatability, since we lose section
information.  Likewise, we lose section-based blacklisting, hmm...)

> My hunch is that we'll save a lot MORE cycles if we bail out of
> dwfl_linux_kernel_report_offline() as soon as we've "reported" all the
> modules we're probing (typically just the kernel).  

I believe we are mostly doing that now (git grep DWARF_CB_ABORT).

> I thought I saw a PR about that, but I can't find it at the moment.

There is bug# 3498 that could help scripts that use some small set of
modules.

- FChE