Fortran 77 complains about common blocks - gcc

Question

I'm using with gfortran 4.8.2 on FreeBSD 9.2 to create some executable files. There are three files, one C file and two Fortran 77 files where I'm using two routines with one common block.
The problem is that I receive an error of multiple definitions from gfortran compiler.
requests which I had sent to server:
autoreconf
./configure
make
di8810.c
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
void main(argc,argv)
int argc;
char *argv[];
{
if (argc != 4)
{
exit(99);
}
gds100(argv[1],argv[2],argv[3]);
}
gds100.f
SUBROUTINE GDS100(AUSGABE,FORMAT,FILENAME)
CHARACTER*4097 EBUF
CHARACTER*264 BUFFER
CHARACTER*1 CBUFFER(264)
CHARACTER*1 CEBUF(4097)
CHARACTER*1 FORMAT
INTEGER*2 INULL
CHARACTER*1 LTEXT(112)
COMMON /GDSCB2/ EBUF
EQUIVALENCE (EBUF,CEBUF(1))
EQUIVALENCE (CEBUF(4097),INULL)
DATA INULL /0/
...
END
gds102.f
SUBROUTINE GDS102
CHARACTER*264 BUFFER
CHARACTER*1 CBUFFER(264)
CHARACTER*4097 EBUF
CHARACTER*1 CEBUF(4097)
INTEGER*2 INULL
INTEGER POIADR
COMMON /GDSCB2/ EBUF
EQUIVALENCE (BUFFER,CBUFFER(1))
EQUIVALENCE (EBUF,CEBUF(1))
EQUIVALENCE (CEBUF(4097),INULL)
DATA IWOGRZ /4096/
DATA INULL /0/
ENTRY GDSUMS(N)
...
END
The error is:
make all-am
gcc -DHAVE_CONFIG_H -I. -DDI88xx -g -O2 -MT src/di8810-di8810.o -MD -MP -MF src/.deps/di8810-di8810.Tpo -c -o src/di8810-di8810.o `test -f 'src/di8810.c' || echo './'`src/di8810.c
mv -f src/.deps/di8810-di8810.Tpo src/.deps/di8810-di8810.Po
gfortran -cpp -fcheck=all -fno-underscoring -DDI88xx -g -O2 -c -o src/di8810-gds100.o `test -f 'src/gds100.f' || echo './'`src/gds100.f
gfortran -cpp -fcheck=all -fno-underscoring -DDI88xx -g -O2 -c -o src/di8810-gds102.o `test -f 'src/gds102.f' || echo './'`src/gds102.f
gfortran -cpp -fcheck=all -fno-underscoring -DDI88xx -g -O2 -o di8810 src/di8810-di8810.o src/di8810-gds100.o src/di8810-gds102.o
src/di8810-gds102.o: In function `gds102':
/.amd_mnt/blnn728x/home/sayik_bo/di8810_t/src/gds102.f:2: multiple definition of `gdscb2'
src/di8810-gds100.o:/.amd_mnt/blnn728x/home/sayik_bo/di8810_t/src/gds100.f:1: first defined here
collect2: Fehler: ld gab 1 als Ende-Status zurück
*** [di8810] Error code 1
Stop in /.amd_mnt/blnn728x/home/sayik_bo/di8810_t.
*** [all] Error code 1
Stop in /.amd_mnt/blnn728x/home/sayik_bo/di8810_t.
Stop in /.amd_mnt/blnn728x/home/sayik_bo/di8810_t.
*** [all] Error code 1
Stop in /.amd_mnt/blnn728x/home/sayik_bo/di8810_t.
It's driving me nuts. Any ideas?

Answer 1

elaborating on my comment
the common statement causes the compiler to allocate global storage for GDSCB2.
The symbols CEBUF,INULL are by Equivalence essentially pointers to the global storage.
Now the two data inull/0/ statements are redundantly initializing the same
location in global memory. I don't know if that a problem or not..just something to look at.
The other thing i see there is inull is 2 bytes (probably..or maybe more but certainly not 1)
yet it is equivalenced to the very last byte of the global character array. ie the initilization writes to data beyond the allocated space.
If at all feasible i would get rid of the common all together. Allocate the storage in the calling program and pass it as an argument to the subroutines.
in any case just do CEBUF(4097)=char(0) instead of using inull like that.