Question

I am trying to write a matlab mex function which uses libhdf5; My Linux install provides libhdf5-1.8 shared libraries and headers. However, my version of Matlab, r2007b, provides a libhdf5.so from the 1.6 release. (Matlab .mat files bootstrap hdf5, evidently). When I compile the mex, it segfaults in Matlab. If I downgrade my version of libhdf5 to 1.6 (not a long-term option), the code compiles and runs fine.

question: how do I solve this problem? how do I tell the mex compilation process to link against /usr/lib64/libhdf5.so.6 instead of /opt/matlab/bin/glnxa64/libhdf5.so.0 ? When I try to do this using -Wl,-rpath-link,/usr/lib64 in my compilation, I get errors like:

/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/../../../../x86_64-pc-linux-gnu/bin/ld: warning: libhdf5.so.0, needed by /opt/matlab/matlab75/bin/glnxa64/libmat.so, may conflict with libhdf5.so.6
/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/../../../../lib64/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
collect2: ld returned 1 exit status

    mex: link of 'hdf5_read_strings.mexa64' failed.

make: *** [hdf5_read_strings.mexa64] Error 1

ack. the last resort would be to download a local copy of the hdf5-1.6.5 headers and be done with it, but this is not future proof (a Matlab version upgrade is in my future.). any ideas?

EDIT: per Ramashalanka’s excellent suggestions, I

A) called mex -v to get the 3 gcc commands; the last is the linker command;

B) called that linker command with a -v to get the collect command;

C) called that collect2 -v -t and the rest of the flags.

The relevant parts of my output:

/usr/bin/ld: mode elf_x86_64
/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/../../../../lib64/crti.o
/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/crtbeginS.o
hdf5_read_strings.o
mexversion.o
-lmx (/opt/matlab/matlab75/bin/glnxa64/libmx.so)
-lmex (/opt/matlab/matlab75/bin/glnxa64/libmex.so)
-lhdf5 (/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/../../../../lib64/libhdf5.so)
/lib64/libz.so
-lm (/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/../../../../lib64/libm.so)
-lstdc++ (/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/libstdc++.so)
-lgcc_s (/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/libgcc_s.so)
/lib64/libpthread.so.0
/lib64/libc.so.6
/lib64/ld-linux-x86-64.so.2
-lgcc_s (/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/libgcc_s.so)
/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/crtendS.o
/usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/../../../../lib64/crtn.o

So, in fact the libhdf5.so from /usr/lib64 is being referenced. However, this is being overriden, I believe, by the environment variable LD_LIBRARY_PATH, which my version of Matlab automagically sets at run-time so it can locate its own versions of e.g. libmex.so, etc.

I am thinking that the crt_file.c example works either b/c it does not use the functions I am using (H5DOpen, which had a signature change in the move from 1.6 to 1.8 (yes, I am using -DH5_USE_16_API)), or, less likely, b/c it does not hit the parts of Matlab internals that need hdf5. ack.

Answer 1

The following worked on my system:

1. Install hdf5 version 1.8.4 (you’ve already done this: I installed the source and compiled to ensure it is compatible with my system, that I get gcc versions and that I get the static libraries – e.g. the binaries offered for my system are icc specific).

2. Make a target file. You already have your own file. I used the simple h5_crtfile.c from here (a good idea to start with this simple file first a look for warnings). I changed main to mexFunction with the usual args and included mex.h.

3. Specify the static 1.8.4 library you want to load explicitly (the full path with no -L for it necessary) and don’t include -lhdf5 in the LDFLAGS. Include a -t option so you can ensure that there is no dynamic hdf5 library being loaded. You also need -lz, with zlib installed. For darwin we also need a -bundle in LDFLAGS:

   mex CFLAGS='-I/usr/local/hdf5/include' LDFLAGS='-t /usr/local/hdf5/lib/libhdf5.a -lz -bundle' h5_crtfile.c -v
   

   For linux, you need an equivalent position-independent call, e.g. fPIC and maybe -shared, but I don’t have a linux system with a matlab license, so I can’t check:

   mex CFLAGS='-fPIC -I/usr/local/hdf5/include' LDFLAGS='-t /usr/local/hdf5/lib/libhdf5.a -lz -shared' h5_crtfile.c -v
   

4. Run the h5_crtfile mex file. This runs without problems on my machine. It just does a H5Fcreate and H5Fclose to create “file.h5” in the current directory, and when I call file file.h5 I get file.h5: Hierarchical Data Format (version 5) data.

Note that if I include a -lhdf5 above in step 3, then matlab aborts when I try to run the executable (because it then uses matlab’s dynamic libraries which for me are version 1.6.5), so this is definitely solving the problem on my system.

Thanks for the question. My solution above is definitely much easier for me than what I was doing before. Hopefully the above works for you.