Re: [RFC/PATCH bpf-next 06/20] libbpf: Factor elf_for_each_symbol function

[Jiri Olsa <olsajiri@gmail.com>]

On Wed, Apr 26, 2023 at 12:27:31PM -0700, Andrii Nakryiko wrote:
> On Mon, Apr 24, 2023 at 9:05 AM Jiri Olsa <jolsa@kernel.org> wrote:
> >
> > Currently we have elf_find_func_offset function that looks up
> > symbol in the binary and returns its offset to be used for uprobe
> > attachment.
> >
> > For attaching multiple uprobes we will need interface that allows
> > us to get offsets for multiple symbols specified either by name or
> > regular expression.
> >
> > Factoring out elf_for_each_symbol helper function that iterates
> > all symbols in binary and calls following callbacks:
> >
> >   fn_match - on each symbol
> >              if it returns error < 0, we bail out with that error
> >   fn_done  - when we finish iterating symbol section,
> >              if it returns true, we don't iterate next section
> >
> > It will be used in following changes to lookup multiple symbols
> > and their offsets.
> >
> > Changing elf_find_func_offset to use elf_for_each_symbol with
> > single_match callback that's looking to match single function.
> >
> 
> Given we have multiple uses for this for_each_elf_symbol, would it
> make sense to implement it as an iterator (following essentially the
> same pattern that BPF open-coded iterator is doing, where state is in
> a small struct, and then we call next() until we get back NULL?)
> 
> This will lead to cleaner code overall, I think. And it does seem func
> to implement it this (composable) way.

ok, I'll check the open-coded iterator for this

> 
> Also, I think we are at the point where libbpf.c is becoming pretty
> bloated, so we should try to split out coherent subsets of
> functionality into separate files. ELF helpers seem like a good group
> of functionality  to move to a separate file? Maybe as a separate
> patch set and/or follow up, but think about whether you can do part of
> that during refactoring?

right, sounds good, will check

thanks,
jirka

> 
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> >  tools/lib/bpf/libbpf.c | 185 +++++++++++++++++++++++++----------------
> >  1 file changed, 114 insertions(+), 71 deletions(-)
> >
> 
> [...]