Re: Why does libca.so depend on libreadline.so?

["Dmitry Yu. Bolkhovityanov via Tech-talk" <tech-talk at aps.anl.gov>]

Hi!

On Mon, 8 May 2023, Han Lee wrote:

> Hi Dmitry,
>
> I think the head file (especially comments in the file) may be what you are
> interested in to get your understanding.
>
> https://github.com/epics-base/epics-base/blob/7.0/modules/libcom/src/osi/epicsReadline.h

Well, this documents the epicsReadline library, but doesn't explain why it 
is required for libCom.

> From my naive understanding, it is required for an iocsh functionality.

Thanks!  The "iocsh" is the keyword.

When googling for "libca.so readline site:anl.gov" I finally encountered a 
message "Re: Problem installing PyEpics" 
(https://epics.anl.gov/tech-talk/2017/msg00206.php) from Andrew Johnson, 
30 Jan 2017, with a short phrase

	    The core of iocsh is a part of libCom.

Yes, this explains it all.

Albeit the design looks extremely surprising -- as if some IP 
implementation included an integrated ksh...


However, a brief investigation had found this had changed in the 7.0.x 
between 7.0.2 and 7.0.7: in 7.0.2 the libca.so.4.13.3 does have a 
dependency on libreadline, while 7.0.7's libca.so.4.14.2 does NOT.

So, if 7.0.x was refactored to get rid of this dependency, then this 
change can probably be back-ported to 3.15.x.  A quick inspection of 
https://epics.anl.gov/base/R7-0/7-docs/RELEASE_NOTES.html doesn't show any 
traces of this change; probably a "diff -Naur" between sources is 
required.  I'm not sure my skills are sufficient for this back-porting, 
but I'll try.


With best regards,
Dmitry



> On Mon, May 8, 2023 at 9:46?PM Dmitry Yu. Bolkhovityanov via Tech-talk <
> tech-talk at aps.anl.gov> wrote:
>
> > Michael,
> >
> > On Sun, 7 May 2023, Michael Davidsaver wrote:
> >
> > > On 5/6/23 23:12, Dmitry Yu. Bolkhovityanov via Tech-talk wrote:
> > > >  P.S. Yes, I'm aware of a "COMMANDLINE_LIBRARY=EPICS" flag (which took
> > some
> > > >  time to figure out :D), but the question remains -- why any commandline
> > > >  editing is needed for network communication libraries at all?
> > >
> > > This is a side-effect of the convention we use to support both dynamic
> > and
> > > static linking
> > > with one configuration.  Since static libraries do not carry dependency
> > > information, when
> > > linking statically it is necessary to give a complete list of all
> > dependent
> > > libraries
> > > when linking any executable.  This includes libreadline when libCom
> > depends
> > > on it.
> > >
> > > One simple way to avoid this over-linking in the dynamic case by passing
> > > "-Wl,--as-needed"
> > > when linking.
> > >
> > > (assumes GCC or clang on an ELF target)
> >
> > Thanks for this -- I didn't know of this linker option!
> >
> > However, I still don't understand: why libCom depends on libreadline (or
> > any commandline-editing library)?
> >
> >
> > With best regards,
> > Dmitry