How to debug with LD_preload - c

Question

I use LD_PRELOAD to override the MPI_Send function with my own function to do some debugging of the MPI_send function.
Here, myMPI_Send.c code:
#define _GNU_SOURCE
#include <stdio.h>
#include <dlfcn.h>
#include <mpi.h>
#include <stdlib.h>
int MPI_Send(const void *buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm)
{
int (*original_MPI_Send)(const void *, int, MPI_Datatype, int, int, MPI_Comm);
original_MPI_Send=dlsym(RTLD_NEXT, "MPI_Send");
printf(" Calling MPI_Send ************** \n");
return (*original_MPI_Send)(buf, count, datatype, dest, tag, comm);
}
In my project, I use an extern library which includes also MPI_Send functions. I need to debug the extern library to know the line and the number of calls of each call of MPI_Send.
I tried to use this code using macros:
fprintf (stderr,"MPI_Send, func <%s>, file %s, line %d, count %d\n",__func__, __FILE__, __LINE__, __COUNTER__);
But, it doesn't work, it prints always the line of MPI_Send in the myMPI_Send.so.
Could you help me please? Thank you in advance.

Answer 1

MPI covers most of your needs via the MPI Profiling Interface (aka PMPI).
Simply redifines the MPI_* subroutines you need, and have them call the original PMPI_* corresponding subroutine.
In you case:
int MPI_Send(const void *buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm)
{
printf(" Calling MPI_Send ************** \n");
PMPI_Send(buf, count, datatype, dest, tag, comm);
}
Since you want to print the line and file of the caller, you might have to use macros and rebuild your app:
#define MPI_Send(buf,count,MPI_Datatype, dest, tag, comm) \
myMPI_Send(buf, count, MPI_Datatype, dest, tag, comm, __func__, __FILE__, __LINE__)
int myMPI_Send(const void *buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm, char *func, char *file, int line)
{
printf(" Calling MPI_Send ************** from %s at %s:%d\n", func, file, line);
return PMPI_Send(buf, count, datatype, dest, tag, comm);
}