cant analysis openmp code with frama-c - c

Question

I'm new in frama-c. I tried to run value analysis plugin on the following c code with openmp directives :
static void kernel_2mm(int ni, int nj, int nk, int nl, float alpha,
float beta, float *tmp, float *A, float *B, float *C, float *D) {
int i, j, k;
/* D := alpha*A*B*C + beta*D */
#pragma omp parallel for collapse(2)
for (i = 0; i < ni; i++)
for (j = 0; j < nj; j++) {
tmp[i * nj + j] = 0.0;
for (k = 0; k < nk; ++k)
tmp[i * nj + j] += alpha * A[i * nk + k] * B[k * nj + j];
}
#pragma omp parallel for collapse(2)
for (i = 0; i < ni; i++)
for (j = 0; j < nl; j++) {
D[i * nl + j] *= beta;
for (k = 0; k < nj; ++k)
D[i * nl + j] += tmp[i * nj + k] * C[k * nl + j];
}
}
But I got the following errors:
rouki#rouki-VirtualBox:~/Téléchargements/frama-c$ frama-c -val 2mm_mp.c
[kernel] Parsing FRAMAC_SHARE/libc/__fc_builtin_for_normalization.i
(no preprocessing)
[kernel] Parsing 2mm_mp.c (with preprocessing)
[kernel] syntax error at 2mm_mp.c:78:
76 int i, j, k;
77 /* D := alpha*A*B*C + beta*D */
78 #pragma omp parallel for collapse(2)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
79 for (i = 0; i < ni; i++)
80 for (j = 0; j < nj; j++) {
[kernel] Frama-C aborted: invalid user input.
When I tried to add -fopenmp flag to the preprocesseur options with:
frama-c -machdep gcc_x86_64 -val -cpp-command 'gcc -fopenmp -C -E -I. ' 2mm_mp.c
I got another error message:
[kernel] Parsing FRAMAC_SHARE/libc/__fc_builtin_for_normalization.i
(no preprocessing)
[kernel] warning: your preprocessor is not known to handle option `-nostdinc'.
If pre-processing fails because of it, please add
-no-cpp-frama-c-compliant option to Frama-C's command-line.
If you do not want to see this warning again, explicitly use option
-cpp-frama-c-compliant.
[kernel] warning: your preprocessor is not known to handle option `-dD'.
If pre-processing fails because of it, please add -no-cpp-frama-c-compliant
option to Frama-C's command-line.
If you do not want to see this warning again, explicitly use option
-cpp-frama-c-compliant.
[kernel] Parsing 2mm_mp.c (with preprocessing)
[kernel] warning: trying to preprocess annotation with an
unknown preprocessor.
[kernel] syntax error at 2mm_mp.c:78:
76 int i, j, k;
77 /* D := alpha*A*B*C + beta*D */
78 #pragma omp parallel for collapse(2)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
79 for (i = 0; i < ni; i++)
80 for (j = 0; j < nj; j++) {
[kernel] Frama-C aborted: invalid user input.
How to make it that frama-c can analyze codes openmp?
Is there a way to force frama-c to use another compiler than gcc (eg: clang, pgcc)?
I use frama-c Phosphorus-20170501 version, with gcc (Ubuntu 5.4.0-6ubuntu1~16.04.5).

Answer 1

Answer to first question (how to make it so that Frama-C can analyze codes with openmp?)
OpenMP pragmas are currently (up to and including Frama-C 16 Sulfur) not supported by Frama-C.
Frama-C tries to parse the pragmas it encounters, and in some cases it will just ignore them, but in other cases (as in the one you encountered) it will try to parse them and fail. Such pragmas are not part of the C standard and constitute compiler extensions that are implementation-defined. Some pragmas, such as #pragma pack(), are supported by Frama-C, on a case by case basis.
Also note that the usage of -cpp-command is no longer recommended if you can use -cpp-extra-args instead. In your case, using this would mean using -cpp-extra-args="-fopenmp". Not that it would help much here, since those pragmas are not supported anyway, but it should avoid the extra warnings you mentioned.
I'm afraid that, currently, the best solution would consist in manually commenting out such pragmas, and then trying to parse the sources again.
Answer to second question (is there a way to force frama-c to use another compiler than gcc (eg: clang, pgcc)?)
Yes, and using -cpp-command as you did is indeed the way to do it. But a good understanding of the C compilation chain is helpful here. In particular, an often recommended approach to deal with some architecture-specific issues (such as custom stdlib headers and non-standard features), is to use the compiler to produce preprocessed code (eg, gcc -E <inputs> -o file.i), and then giving that file to Frama-C.
Note that in the case of OpenMP in particular, the pragmas used by GCC are not removed by preprocessing (which is logical, since it uses those pragmas after preprocessing, during the compilation itself), so it wouldn't help in your case. But it does help, for instance, when using MSVC-specific code that includes several stdlib headers from the Microsoft SDK that are incompatible with those from the GNU libc).
Finally, remember that Frama-C uses gcc (or another compiler) only for preprocessing the sources; the rest of the compilation chain is not used. Therefore, it is not often the case that switching from GCC and Clang changes the result, since both implement very similar features in terms of preprocessing. Again, it is often possible to use exclusively -cpp-extra-args instead of -cpp-command, which was recommended mainly when -cpp-extra-args did not exist yet.