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Compiler/Linker question

 
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wahorger



Joined: 13 Oct 2014
Posts: 851
Location: Morrison, CO, USA

PostPosted: Sun May 10, 2020 4:04 pm    Post subject: Compiler/Linker question Reply with quote

If I have a routine that contains a declaration that reads either :
Code:
EXTERNAL ABCD
.
or
.
INTEGER,EXTERNAL:: ABCD


and the routine in which this appears does not reference the external ABCD in any way, will ABCD be required to be present as an object or in a .lib or .dll at link time?
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LitusSaxonicum



Joined: 23 Aug 2005
Posts: 2187
Location: Yateley, Hants, UK

PostPosted: Sun May 10, 2020 10:29 pm    Post subject: Reply with quote

I've had a go at this, and FTN95 reports that the variable is unused as a warning, and using -LGO the executable seems to run OK. This came as a surprise to me, because I was expecting a report that there was a missing reference.

(Edit) It used to be said that you should not use unnamed BLOCK DATA routines but should name it/them and include the name(s) in EXTERNAL statements so that the compiler would report if the routine(s) had been omitted. I used so many compilers that were subset and didn't support BLOCK DATA that I never used it, and I see that BLOCK DATA is no longer favoured anyway. The need to initialise or reinitialise large data structures still exists, and BLOCK DATA or compiler initialisation only works once. If I have to initialise and reinitialse then I do it with executable assignment statements in a subroutine that I name BLOCKDATA!

E
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wahorger



Joined: 13 Oct 2014
Posts: 851
Location: Morrison, CO, USA

PostPosted: Mon May 11, 2020 2:29 pm    Post subject: Reply with quote

Eddie, thanks for the test and your observations.

This has nothing to do with BLOCK DATA (I do use it, but not as you described).

My interest is only in the actual code. For example, if I have 5 or 10 routines in a file, compile it, place it in a library, and link to one of them, all of them are loaded. I'm looking to see if the same phenomena exists if I have an EXTERNAL declaration to that routine, but the routine is never called (it is an excessive declaration).

Over the years, these have crept into the code, and I am wondering , while I have some time now, whether to invest time in cleaning these up.
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DietmarSiepmann



Joined: 03 Jun 2013
Posts: 244

PostPosted: Tue May 12, 2020 3:40 pm    Post subject: Reply with quote

wahorger,

if library is used with the meaning archive (as opposed to import library), then I would like to point to option /mklib which "generates a static library containing a separate object for each function or subroutine" (quoted from ftn95 online help).

This option is, however, only available for WIN32.

Wouldn't that help in the sample you mentioned?

Regards,
Dietmar
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wahorger



Joined: 13 Oct 2014
Posts: 851
Location: Morrison, CO, USA

PostPosted: Wed May 13, 2020 12:57 am    Post subject: Reply with quote

Dietmar, I will certainly take a look at this, although I think the question still remains whether an unused EXTERNAL will cause the module to be linked in.

Bill
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DietmarSiepmann



Joined: 03 Jun 2013
Posts: 244

PostPosted: Wed May 13, 2020 10:35 am    Post subject: Reply with quote

wahorger,

I suspect that linking against libraries built with/mklib will prevent a routine declared as external but never called from being "loaded" into the executable. Please look at the souces main.for
Code:

      integer*4 x,y,z
      external mult
      x=2
      y=3
      write(*,*) 'x=',x,'    y=',y
      call sum(x,y,z)
      write(*,*) 'sum: z=',z
      end

and libsrc.for
Code:

      subroutine sum(a,b,c)
        integer*4 a,b,c
        c=a+b
      end
     
      subroutine mult(a,b,c)
        integer*4 a,b,c
        c=a*b
      end

. Using script build.bat
Code:

@echo off
setlocal
  SET DEBUG_OPT=/debug
  ftn95 %DEBUG_OPT% libsrc.for
  slink libsrc1.lnk
  ftn95 %DEBUG_OPT% libsrc.for /mklib
  ftn95 %DEBUG_OPT% main.for
  slink main.lnk
  slink main1.lnk
endlocal

archive libsrc.lib is built with /mklib, archive libsrc1.lib is built without /mklib, main.exe is linked against libsrc.lib, main1.exe is linked against libsrc1.lib. Looking into both executables via a hex editor you see that mult is not contained in main.exe, but in main1.exe. You might also want to use commands
Code:

dumpbin main.exe /all
dumpbin main1.exe /all

and see that string
Code:

SECT1  notype ()    External     | _MULT

does not occur in the output of the first dumpbin command, but in that of the second.
The lnk files used are main.lnk
Code:

lo main
lo libsrc.lib
file main.exe

, main1.lnk
Code:

lo main
lo libsrc1.lib
file main1.exe

and libsrc1.lnk
Code:

archive libsrc1.lib
addobj libsrc.obj
file


Regards
Dietmar
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wahorger



Joined: 13 Oct 2014
Posts: 851
Location: Morrison, CO, USA

PostPosted: Wed May 13, 2020 2:35 pm    Post subject: Reply with quote

Dietmar,

Thanks for the additional explanation. I looked up /mklib and I already use SLIM to build my library.

Since my library is built using SLIM, I finally set aside some time for this. I generated a couple of test cases and inserted them into my compilations. I had a couple of questions to answer. I hope others may find this useful.

If I have an EXTERNAL declaration, but never reference the containing routine in the compilation of the containing module/routine, there is no attempt to link that EXTERNAL into the executable. This is good! One less thing to look for (until final clean-up).

If I have a subroutine/function that exists in a file being compiled, yet the routine is never referenced, does it get loaded into the resultant executable? The answer is yes!

This is beneficial to know because as one proceeds in development, sometimes a utility function (or group of them) may be coalesced as differently named routines. I know I have several of these, so I should search them out, especially if they have any large, static data declarations; these will take up room in the executable for no purpose. I have over 1500 individual routines in over 300 files to search through. I may have to write a tool.....

Thanks,
Bill
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