Question

I am trying to replace some graphics code in a set of fortran programs (not my own code). I got one of the simpler ones (‘psvdraw’) to work just fine, replacing the fortran postscript-generating code with C calls that call the Cairo library (graphic_output.c). I have been able to successfully work out the cross-language calls without too much trouble.

However, when trying to get the second, larger program (‘pssect’) to work, calling the same C code, I get Segmentation Faults, or in some cases, the program flow goes back to a fortran routine ‘error’ (I do not call this, or any fortran routine in my C code).

In trying to diagnose this problem, I linked in a bunch of the fortran code from pssect into psvdraw (‘biglib.f’), and got the same errors. Note that none of this added code is actually called! Also the errors occur right at the first call from fortan into the c code. So: psvdraw with biglib.f linked in fails, but psvdraw without it succeeds.

Here are relevant bits of the makefile:

Makefile

COMP77 = gfortran

FFLAGS = -C -v -pedantic -Wunused -fno-underscoring

CC = gcc-4
CFLAGS = -v -pedantic -Wunused
CAIRO_INCLUDE = /sw/include/cairo
CAIRO_LIB = /sw/lib

# PSVDRAW Make setup that works:
psvdraw: psvdraw.o graphic_output.o tlib.o pscom.o
    $(COMP77) $(FFLAGS) $@.o graphic_output.o tlib.o pscom.o -L$(CAIRO_LIB) -lcairo -o $@

# PSVDRAW Make setup with errors:
#psvdraw: psvdraw.o graphic_output.o tlib.o pscom.o biglib.o
#   $(COMP77) $(FFLAGS) $@.o graphic_output.o  pscom.o tlib.o biglib.o -L$(CAIRO_LIB) -lcairo -o $@

pssect: pssect.o graphic_output.o pscom.o tlib.o biglib.o 
    $(COMP77) $(FFLAGS) $@.o graphic_output.o pscom.o tlib.o biglib.o -L$(CAIRO_LIB) -lcairo -o $@

pssect.o: pssect.f
    $(COMP77) $(FFLAGS) -c pssect.f
psvdraw.o: psvdraw.f
    $(COMP77) $(FFLAGS) -c psvdraw.f
pscom.o: pscom.f
    $(COMP77) $(FFLAGS) -c pscom.f
tlib.o: tlib.f
    $(COMP77) $(FFLAGS) -c tlib.f
biglib.o: biglib.f
    $(COMP77) $(FFLAGS) -c biglib.f

graphic_output.o: graphic_output.c
    $(CC) $(CFLAGS) $(INCL) -c -I$(CAIRO_INCLUDE) graphic_output.c

.c.o:
    $(CC) $(CFLAGS) $(INCL) -c $<

.f.o:
    $(FC) $(FFLAGS) $(INCL) -c $<

Here is the offending fortran code: Note that the problem occurs right at the beginning of the program:

Beginning of pssect.f:

PROGRAM PSSECT

implicit none

include 'perplex_parameters.h'

integer jop0, ier99

logical vertex, output, first

character*100 fname, yes*1

integer  iop0 
logical  debug
common / basic /iop0, debug

integer isec,icopt,ifull,imsg,io3p
common/ cst103 /isec,icopt,ifull,imsg,io3p
c----------------------------------------------------------------------
c   Look for the "debug_yes" file to turn on debugging messages
PRINT *,'Pre-PSOPEN1'
call psopen ('plot2')    
PRINT *,'Post-PSOPEN1'

And here is part of the c code that gets called and produces a fault:

Part of graphic_output.c:

char dmh_debug = 0;

#define DEBUGPRINT(x) if (dmh_debug) {printf x;};

void psopen(char *fname, int fnamelen) {

    printf("Debug opened\n");

    char *outFileName;
    char outputType[255];
    char pageWidthString[255];
    char pageHeightString[255];

    /* Set debug status based upon presence of file named 'debug_yes' in directory */
    FILE *debugFile = fopen("debug_yes", "r");
    if (debugFile == NULL) {
        dmh_debug = 0;
    } else {
        dmh_debug = 1;
    }
    fclose(debugFile);

    dmh_debug = 1;
    DEBUGPRINT(("Debug closed\n"));

    fname[fnamelen]='\0';
    fname = trim(fname);
    outFileName = malloc((strlen(fname) + 50) * sizeof(char));
    strcpy(outFileName, fname);
    DEBUGPRINT(("Found file name:%s of length: %lu\n", fname, strlen(fname)));
[...]

Results of running the program

pnr-rethington:source dave$ ./pssect
 Pre-PSOPEN1
Debug opened
Segmentation fault

Answer 1

Running under the debugger (gdb) should tell you where the segfault happens. Compile all code with -O0 -g to get accurate information.