Tcl version change issue from 8.4 to 8.5.12

Question

I have a problem with changing tcl version from 8.4 to 8.5.12 on RHEL machine. Our product uses TclDevKit components like Tcldom, Tclxml, etc. Also we are using Incr Tcl (Itcl). I am trying to create pkgIndex.tcl file in Itcl in order to find Itcl when that package is required as follown:

package ifneeded Itcl 3.4 [list load [file join $dir "libitcl-O.a"] Itcl ]

but when I use

package require Itcl

Getting report: couldn't load file "/somepath/itcl/lib/libitcl-O.a": /somepath/lib/libitcl-O.a: invalid ELF header

It seems I can't load files with .a extention, but the same is done with previous version of tcl (8.4) and it works fine. I googled a lot, read a lot of documentation, but it doesn't help to go further.

Please help.

Thanks in advance

Answer 1

Libraries come in two general sorts, static libraries and shared libraries. On Linux, static libraries have the extension .a by default, and shared libraries have the extension .so (plus optionally some numbers to indicate the version). Only shared libraries will work with Tcl's load command and even then they have to be designed to work that way (with an appropriate Foobar_Init function, as documented).

When dealing with stub-exporting extensions (fairly rare) or Tcl and Tk themselves, the linking is done in two parts. There's a stub library, normally called somethingstub.a, and there's a main shared library. The main shared library contains the implementation of the code; all that is in the stub library is an ABI/API adaptor so that you can avoid binding your code to an explicit version of the implementation library. By building an extension stub-enabled and linking against the stub library, you gain the ability to have your extension loaded into future versions of Tcl/Tk without any recompilation or relinking steps at all. (You also become able to put the extension inside a starkit for deployment, as those use a rather unusual way of managing shared libraries that the stub mechanism conceals from you.)