mex compilation - undefined reference to `main'

I am trying to compile Matlab interface of NOMAD algorithm (https://www.gerad.ca/nomad/Project/Home.html) in Ubuntu 14.04 using gcc-4.7.3.

After executing compilation script provided by algorithm manufacturer I get the following error:

>> GERAD_NOMAD_build

------------------------------------------------
NOMAD MEX FILE BUILD --- GERAD VERSION 

Warning: Legacy MEX infrastructure is provided for compatibility; it will be removed in a future
version of MATLAB. For more information, consult the MEX release notes
http://www.mathworks.com/help/matlab/release-notes.html. 
> In GERAD_NOMAD_build (line 145) 
-> mexopts.sh sourced from directory (DIR = $PREF_DIR)
   FILE = /home/bkhusain/.matlab/R2015a/mexopts.sh
----------------------------------------------------------------
->    MATLAB                = /usr/local/MATLAB/R2015a
->    CC                    = gcc
->    CC flags:
         CFLAGS             = -ansi -D_GNU_SOURCE  -fexceptions -fPIC -fno-omit-frame-pointer -pthread -std=c99
         CDEBUGFLAGS        = -g
         COPTIMFLAGS        = -O -DNDEBUG
         CLIBS              = -Wl,-rpath-link,/usr/local/MATLAB/R2015a/bin/glnxa64 -L/usr/local/MATLAB/R2015a/bin/glnxa64 -lmx -lmex -lmat -lm
         arguments          = 
->    CXX                   = g++
->    CXX flags:
         CXXFLAGS           = -ansi -D_GNU_SOURCE -fPIC -fno-omit-frame-pointer -pthread
         CXXDEBUGFLAGS      = -g
         CXXOPTIMFLAGS      = -O -DNDEBUG
         CXXLIBS            = -Wl,-rpath-link,/usr/local/MATLAB/R2015a/bin/glnxa64 -L/usr/local/MATLAB/R2015a/bin/glnxa64 -lmx -lmex -lmat -lm
         arguments          = 
->    FC                    = gfortran
->    FC flags:
         FFLAGS             = -fexceptions -fbackslash -fPIC -fno-omit-frame-pointer
         FDEBUGFLAGS        = -g
         FOPTIMFLAGS        = -O
         FLIBS              = -Wl,-rpath-link,/usr/local/MATLAB/R2015a/bin/glnxa64 -L/usr/local/MATLAB/R2015a/bin/glnxa64 -lmx -lmex -lmat -lm
         arguments          = 
->    LD                    = g++
->    Link flags:
         LDFLAGS            =  -Wl,-rpath,'/../lib/' 
         LDDEBUGFLAGS       = -g
         LDOPTIMFLAGS       = -O
         LDEXTENSION        = .mexa64
         arguments          =  -lut -lnomad -L/home/bkhusain/nomad.3.7.3/lib/
->    LDCXX                 = 
->    Link flags:
         LDCXXFLAGS         = 
         LDCXXDEBUGFLAGS    = 
         LDCXXOPTIMFLAGS    = 
         LDCXXEXTENSION     = 
         arguments          =  -lut -lnomad -L/home/bkhusain/nomad.3.7.3/lib/
----------------------------------------------------------------

-> g++ -c  -I. -I/home/bkhusain/nomad.3.7.3/src/ -I/usr/local/MATLAB/R2015a/extern/include -I/usr/local/MATLAB/R2015a/simulink/include -DMATLAB_MEX_FILE -ansi -D_GNU_SOURCE -fPIC -fno-omit-frame-pointer -pthread  -O -DNDEBUG  "nomadmex.cpp"

-> g++ -O  -Wl,-rpath,'/../lib/'  -o  "/home/bkhusain/nomad.3.7.3/bin//nomad.mexa64"  nomadmex.o  -lut -lnomad -L/home/bkhusain/nomad.3.7.3/lib/ -Wl,-rpath-link,/usr/local/MATLAB/R2015a/bin/glnxa64 -L/usr/local/MATLAB/R2015a/bin/glnxa64 -lmx -lmex -lmat -lm

/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 0 has invalid symbol index 11
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 1 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 2 has invalid symbol index 2
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 3 has invalid symbol index 2
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 4 has invalid symbol index 11
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 5 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 6 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 7 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 8 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 9 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 10 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 11 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 12 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 13 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 14 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 15 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 16 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 17 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 18 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 19 has invalid symbol index 21
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_line): relocation 0 has invalid symbol index 2
/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
collect2: error: ld returned 1 exit status

      mex: link of ' "/home/bkhusain/nomad.3.7.3/bin//nomad.mexa64"' failed.

Error using GERAD_NOMAD_build (line 166)
Error Compiling NOMAD!
Unable to complete successfully.

The error is thrown after executing:

mex -v -largeArrayDims nomadmex.cpp LDFLAGS='$LDFLAGS -Wl,-rpath,''$ORIGIN/../lib/'' '  -I.  -I/home/bkhusain/nomad.3.7.3/src/ -lut -lnomad -L/home/bkhusain/nomad.3.7.3/lib/ -output /home/bkhusain/nomad.3.7.3/bin//nomad.mexa64

I don't understand why linker is complaining about missing reference to 'main', since main function is not required for mex compilation.

Answer 1

[Bulat Khusainov]

The problem was solved by adding the directory of required *.so files to the path manually. In ~/.bashrc I added:

LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/home/bkhusain/Documents/MATLAB/nomad.3.7.3/lib
export LD_LIBRARY_PATH

Also when calling mex I removed LDFLAGS:

mex -v -largeArrayDims nomadmex.cpp -I.  -I/home/bkhusain/nomad.3.7.3/src/ -lut -lnomad -L/home/bkhusain/nomad.3.7.3/lib/ -output /home/bkhusain/nomad.3.7.3/bin//nomad.mexa64

Still I do not understand why linker was looking for main() function. I will try to investigate this based on answer Jan Simon's answer

Answer 2

[Jan]

I hesitate to register at the web page only to answer your question. The linker claims, that the function "main" is called from the function "_start". So either lokk in the source code to find explanations or ask the author.