Tcl8.6.5 USE_TCL_STUBS tclDecls.h # undef Tcl_StaticPackage,

Question

I am trying to rebuild some software originally built against Tcl/Tk8.2 which used the libtclstubs.a and libtkstubs.a static libraries. Now I am able to recompile against -ltclstub8.6 -ltkstub8.6 from the Ubuntu Xenial, tcl8.6-dev:amd64 8.6.5+dfsg-2 package, but I get the linker errors:

undefined reference to `Tcl_StaticPackage'
undefined reference to `Tcl_FindExecutable'

I have traced this down to the following code block in tclDecls.h

/* !END!: Do not edit above this line. */

#if defined(USE_TCL_STUBS)
#   undef Tcl_CreateInterp
#   undef Tcl_FindExecutable
#   undef Tcl_GetStringResult
#   undef Tcl_Init
#   undef Tcl_SetPanicProc
#   undef Tcl_SetVar
#   undef Tcl_ObjSetVar2
#   undef Tcl_StaticPackage
#   undef TclFSGetNativePath
#   define Tcl_CreateInterp((tclStubsPtr->tcl_CreateInterp())
#   define Tcl_GetStringResult(interp
               (tclStubsPtr->tcl_GetStringResult(interp))
#   define Tcl_Init(interp) (tclStubsPtr->tcl_Init(interp))
#   define Tcl_SetPanicProc(proc)          (tclStubsPtr->tcl_SetPanicProc(proc))
#   define Tcl_SetVar(interp, varName, newValue, flags) \
        (tclStubsPtr->tcl_SetVar(interp, varName, newValue, flags))
#   define Tcl_ObjSetVar2(interp, part1, part2, newValue, flags) \
        (tclStubsPtr->tcl_ObjSetVar2(interp, part1, part2, newValue, flags))
#endif

Obviously the macros that redefine Tcl_StaticPackage and Tcl_FindExecutable earlier in the header file are annulled and not redeclared here. Presumably I can just redefine them within my own code after the include statement. So I guess I'm wondering, is there a reason behind the "undef" statements, will they go away in the future and did I just pick a bad version to build against?

For the record, this is regarding an old mixed language, Fortran77 main program that initiates several tcl interpreters and custom drawing widgets via a C interface.

EDIT: to show linking command

    gfortran -O3  -fno-automatic -std=legacy -ffixed-form  -rdynamic \
  -o ../bin/xtal_37.exe             aa.lnx_o ab.lnx_o ad.lnx_o ap.lnx_o \
ar.lnx_o at.lnx_o ax.lnx_o ay.lnx_o az.lnx_o bn.lnx_o bt.lnx_o bu.lnx_o \
by.lnx_o cb.lnx_o cf.lnx_o cg.lnx_o ci.lnx_o cl.lnx_o cn.lnx_o cp.lnx_o \
cr.lnx_o cu.lnx_o dd.lnx_o fb.lnx_o fc.lnx_o fe.lnx_o fr.lnx_o fs.lnx_o \
ge.lnx_o gs.lnx_o gt.lnx_o lc.lnx_o lf.lnx_o ls.lnx_o mh.lnx_o ml.lnx_o \
mp.lnx_o nc.lnx_o nm.lnx_o or.lnx_o pa.lnx_o pb.lnx_o pe.lnx_o pg.lnx_o \
pn.lnx_o po.lnx_o pp.lnx_o px.lnx_o pv.lnx_o rb.lnx_o re.lnx_o rf.lnx_o \
rs.lnx_o rv.lnx_o rw.lnx_o sh.lnx_o si.lnx_o sl.lnx_o sp.lnx_o sr.lnx_o \
sx.lnx_o vu.lnx_o xt.lnx_o mx.lnx_o ed.lnx_o cm.lnx_o os.lnx_o dm.lnx_o \
sf.lnx_o     surfin.lnx_o togl.lnx_o tklib.lnx_o datim.lnx_o bitws.lnx_o \
lnblnk.lnx_o qsort.lnx_o          ciftbx.lnx_o hashfunc.lnx_o clearfp.lnx_o \
         -L/usr/X11R6/lib  -L/usr/lib/x86_64-linux-gnu/   -L/usr/lib  \
    -ltclstub8.6 -ltkstub8.6 -ldl -lX11 -lGL -lXmu 

EDIT: to show fix by redeclaring defs after #include

#include <tk.h>
#
#if defined(USE_TCL_STUBS)
#define Tcl_FindExecutable \
        (tclStubsPtr->tcl_FindExecutable) /* 144 */
#define Tcl_StaticPackage \
        (tclStubsPtr->tcl_StaticPackage) /* 244 */
#endif

-which works, but I just don't know why they are "#undef" in the second place.

Answer 1

Background

You did not respond to my comment, but for some background: Prior to 8.6, Tcl_FindExecutable() could be called via the Tcl stubs table, which turned out to be an issue of unwanted circularity: Tcl_FindExecutable() must be called (callable) before an interpreter has been created (Tcl_CreateInterp()), initialising the stub tables assumes a working interpreter, though. See, e.g., Ticket #8419b6d9ae for a reference.

So ... the #undef Tcl_FindExecutable removes the macro (after it has just been added) to make this unintended use less likely (but does not prevent it, as shown by your patch).

Suggestions

Your application (xtal.exe) does not seem to be intended as a Tcl extension reaping the benefits of a stubs mechanism at all, so built it as a standalone application with -ltcl86 and omit -DUSE_TCL_STUBS in the compile step? In any case, to obtain a valid reference to Tcl_FindExecutable, you will have to include -ltcl86, whether using stubs or not.