Unable to use compiled netlib BLAS on mac OS X - c

Question

I'm trying to make a repository collecting all the examples, tutorials and instructions I could find on the internet for C mathematical and algebra libraries (BLAS, CBLAS, LAPACK, CLAPACK, LAPACKE, ATLAS, openblas, GSL...). but it seems that I just can't get the compiled BLAS .a files working on mac OS X.
So far I have been able to compile BLAS and use it on ubuntu:
BLAS source code from netlib website downloaded and compiled (rename blas_LINUX.a to libblas.a)
Then I can compile the C file on ubuntu using the command below:
gcc foo.c path/to/libblas.a
On my mac OS X (EL Capitan), I can compile BLAS (changing LINUX in the make.inc to DARWIN), but when I try to compile a C code using the command above I get errors like below:
Undefined symbols for architecture x86_64:
"_ddot_", referenced from:
_main in foo-3a35db.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
("ddot" part differs for different functions)
possibilities:
Maybe I'm not compiling the library correctly on mac and there are some differences I'm not aware of
The builtin Accelerate framework of mac OS X is messing up with the compiling process
P.S. Guys I know BLAS/LAPACK is already built into the mac OS X Accelerate framework and I can easily compile using the command gcc foo.c -lblas or gcc foo.c -framework Accelerate but I want to use the compiled .a from netlib. I want to know why it works properly on ubuntu but not mac OS X?
P.S.2. Please notice that I can compile the source code successfully without any errors on mac OS X. I just can use it!
Example code: source
#include <stdio.h>
#include <stdlib.h>
double ddot_(const int *N, const double *a, const int *inca, const double *b, const int *incb);
int main(int argc, char **argv) {
double *a = (double *)malloc(3 * sizeof(double));
a[0] = 1.0;
a[1] = 2.0;
a[2] = 3.0;
// on the stack
double b[3] = {4.0, 5.0, 6.0};
int N = 3, one = 1; // one really doesn't look good in C
double dot_product = ddot_(&N, a, &one, b, &one);
printf(" The dot product is: %f \n", dot_product);
return 0;
}
(edit1) solution:
open make.inc
change the line OPTS = -O3 to OPTS = -O3 -pipe -c and make.
(edit2): better solution:
since I asked this question I have realised that I have been doing everything wrong. Netlib BLAS is actually a collection of fortran routines/subroutines/functions. and the Makefile in the source code just gives us a static library libblas.a which is a collection of all .o object files compiled with gfortran. when we want to compile a C code which want to call one of those routines, we also need to link to the gfortran library libgfortran.* so if you have gcc installed (brew install gcc). look for libgfrotran* (sudo find / -name "libgfortrn.*") and then link your gcc to this folder too. to make it easy I put a Makefile here:
all:
gcc -c foo.c
gcc -o bar.out foo.o -L path/to/libgfortran.*/ -lgfortran -L path/to/libblas.a -lblas
or alternatively compile the code directly with gfortran:
all:
gcc -c foo.c
gfortran -o bar.out foo.o -L path/to/libblas.a -lblas
or simply compile with:
gcc foo.c bar.out -L path/to/libblas.a -lblas -L path/to/libgfortran.*/ -lgfortran
the wonder is how/why the former solution actually worked and why on ubuntu you don't have to link to -lgfortran!

Answer 1

It seems you compiled BLAS library from Netlib with compiler options that changed the mangling scheme of Fortran routines.
By default, Netlib's make.inc uses gfortran to compile BLAS:
$ grep FORTRAN make.inc
# Modify the FORTRAN and OPTS definitions to refer to the
FORTRAN = gfortran
It is compiled without any flags:
gfortran -O3 -pipe -c ddot.f -o ddot.o
and you get the ddot() routine:
$ grep -i ddot ddot.o libblas.a
Binary file ddot.o matches
Binary file libblas.a matches
And you can find it with the command line tools:
$ nm ddot.o libblas.a | grep -i ddot
ddot.o:
0000000000000000 T _ddot_
libblas.a(ddot.o):
0000000000000000 T _ddot_
Your example compiles with the library:
cc ex.c libblas.a
or with the ddot.o file:
cc -pipe ex.c ddot.o
I cannot reproduce your problem. You should use the nm and grep commands to find out what happened to the name of the ddot() routine.
PS. Your code has extra semicolon ; after the end of definition of main().