Experimental Physics and
Industrial Control System

"Dmitry Yu. Bolkhovityanov via Tech-talk" <tech-talk at aps.anl.gov> · Wed, 10 May 2023 15:06:03 +0700 (+07)

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

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System