Computer Engineering [closed] - linux

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cse85054#kinpenguin:~$ g++ main.cpp -o newprog1 /usr/bin/ld: /tmp/cc2rjmRM.o: in function main':
main.cpp:(.text+0x14): undefined reference to print_hello()' /usr/bin/ld: main.cpp:(.text+0x20): undefined reference to print_progname(char**)'
/usr/bin/ld: main.cpp:(.text+0x2a): undefined reference to `print_argcount(int)'
collect2: error: ld returned 1 exit status
I get this error when I try to link my main.cpp to shared library files. I created all the .cpp files correctly including the header. If I do not use dynamic linking it works correctly.
I created the shared object using this command:
g++ -Wall -c -fPIC *.cpp
Then I created shared objects:
g++ -shared -o functions-1.o
Then I tried linking my main to the shared library file when I am running into the error. I have already set the LD_PATH variable.
These are all the files in my current directory:
header.h main.cpp print_argcount.cpp print_hello.cpp
hello main.o print_argcount.o print_hello.o
hiii makefile print_arglist.cpp print_progname.cpp newprog print_arglist.o print_progname.o


gcc dialog library not linking

I'm trying to develop a small utility using the dialog library in C (the dialog command in linux).
On fedora linux works fine, but if i try to compile it on debian with the command:
gcc -ldialog -lncurses -I/usr/include dialog_test.c
I get the following error:
vetinari#ankhmorpork:~/Projects/Other/test$ gcc -ldialog -I/usr/include dialog_test.c
/usr/bin/ld: /tmp/ccX6fPYB.o: warning: relocation against `dialog_vars' in read-only section `.text'
/usr/bin/ld: /tmp/ccX6fPYB.o: in function `main':
dialog_test.c:(.text+0x5c): undefined reference to `init_dialog'
/usr/bin/ld: dialog_test.c:(.text+0x79): undefined reference to `dialog_yesno'
/usr/bin/ld: dialog_test.c:(.text+0xae): undefined reference to `dialog_menu'
/usr/bin/ld: dialog_test.c:(.text+0xbc): undefined reference to `dialog_vars'
/usr/bin/ld: dialog_test.c:(.text+0xc5): undefined reference to `end_dialog'
/usr/bin/ld: warning: creating DT_TEXTREL in a PIE
collect2: error: ld returned 1 exit status
The dialog command works fine.
Anyone has any idea why it isn't working on debian?
(Answer for the wiki sake, in case someone comes by here later)
You have to put the libraries you want to link at the end of the gcc command, like this:
gcc dialog_test.c -ldialog -lncurses
The reason is explained here: The way the linker looks up symbols it has to first see the reference, and then the library prodiving the symbol
Additionally, the dialog library might have other dependencies than ncurses. There is explanation how to find out what to include and what to link here, in short: dialog-config should tell you about it.
In this specific case, what worked for me (ubuntu 20.04) was linking ncursesw instead of ncurses.
After that, I was left with an
undefined reference to `sqrt'
linker error, which can be solved by linking the match library using -lm.
So, in total, this command works:
gcc dialog_test.c -ldialog -lncursesw -lm

Question about compiling sources code with HDF5 and mpi

When I am trying to compile the source code by 'make', the first steps that creating the '.o' files are running fine, and all '.o' files could be compiled normally. However, when compiling the executable file:
mpifort -fopenmp -O3 -o MyEXE sth.o main.o -L/usr/local/share/fftw-3.3.8/lib -lfftw3_mpi -lfftw3 -lm -L/usr/local/share/mpich-3.2/lib -lmpi -lz -L/usr/local/share/hdf5-1.8.18/lib -lhdf5_fortran -lhdf5hl_fortran -lhdf5_hl -lhdf5 -fPIC
it gots the following error:
/usr/bin/ld: /usr/local/share/hdf5-1.8.18/lib/libhdf5.a(H5PL.o): undefined reference to symbol 'dlclose##GLIBC_2.2.5'
//lib/x86_64-linux-gnu/ error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status
How could I solve this problem? Some pages suggest that it is due to the '-ldl- flag when calling c++ compiler, but I couldn't find a way to make it suitable for my cases.
The pages were right. Your HDF5 library libhdf5.a uses the function dlclose, which is defined in the library libdl. To use it, you need to simply add -ldl at the end of your mpifort command line.

Build a program with GLFW3 on Linux

I know this question has been asked many times before but I have been trying to get this working for days and none of the current answers solve my problem. I'd appreciate not being linked to this post: How to build & install GLFW 3 and use it in a Linux project Most of the answers I have seen redirect there but I have gone through it thoroughly and am still having problems.
I am running Linux Mint 17.1.
I have downloaded and built GLFW 3.1.1:
*Downloaded source; extracted; terminal to extract directory*
cmake .
make install
I have also downloaded the example program at
I am using the following build commands:
g++ -std=c++11 -c HelloGLFW.cpp
g++ HelloGLFW.o -o main.exec -lGL -lGLU -lglfw3 -lX11 -lXxf86vm -lXrandr -lpthread -lXi
The program compiles fine but when I try to link it I get these errors:
//usr/local/lib/libglfw3.a(x11_init.c.o): In function `initExtensions':
x11_init.c:(.text+0x1aeb): undefined reference to `XineramaQueryExtension'
x11_init.c:(.text+0x1b05): undefined reference to `XineramaIsActive'
//usr/local/lib/libglfw3.a(x11_init.c.o): In function `_glfwCreateCursor':
x11_init.c:(.text+0x21f9): undefined reference to `XcursorImageCreate'
x11_init.c:(.text+0x22d0): undefined reference to `XcursorImageLoadCursor'
x11_init.c:(.text+0x22e0): undefined reference to `XcursorImageDestroy'
//usr/local/lib/libglfw3.a(x11_monitor.c.o): In function `_glfwPlatformGetMonitors':
x11_monitor.c:(.text+0x6e9): undefined reference to `XineramaQueryScreens'
collect2: error: ld returned 1 exit status
I have also gone through the instructions on the GLFW website but they seem to be quite lacking for Linux. I have gotten it working on Linux before but that was a year ago and I can't replicate it.
Can someone please let me know all the steps required to build a program with GLFW3 on Linux (including all dependencies required)?
When glfw3 was installed using cmake a file glfw3.pc was created along with it. This is a pkg-config file and lists what libraries are required for linking.
For me this file was located in /usr/local/lib/pkgconfig
The command I used to successfully build the program with was:
g++ HelloGLFW.cpp -lglfw3 -lX11 -lXrandr -lXinerama -lXi -lXxf86vm -lXcursor -lGL -lpthread
The GLFW site does list details at but it's a bit unclear what to look for if you aren't that familiar with Linux systems.
Specificity the instructions list this command for compiling with the static glfw3 library:
cc `pkg-config --cflags glfw3` -o myprog myprog.c `pkg-config --static --libs glfw3`
and with the dynamic glfw3 library:
cc `pkg-config --cflags glfw3` -o myprog myprog.c `pkg-config --libs glfw3`

Cross-compiling Snap7 for MIPS with OpenWrt as OS

Currently i'm working on a project to log data out of a Siemens PLC. To achieve this i'm using Snap7. Snap7 ( is a communication library.
I've managed to get it work on my linux desktop but when i try to cross-compile the snap7 library i get some errors
The error is generated when linking all of the object files.
g++ -shared -fPIC -o ../bin/mips-openwrt-linux-g++/ #"filelist.txt" -L. -lpthread -lrt -O3
/usr/bin/ld: ../temp/mips-openwrt-linux/sys_snap_msgsock.o: Relocations in generic ELF (EM: 8)
./temp/mips-openwrt-linux/sys_snap_msgsock.o: could not read symbols: File in wrong format
collect2: error: ld returned 1 exit status
make: *** [../bin/mips-openwrt-linux-g++/] Error 1
If i'm correct i think it's using the wrong linker, it should use the linker of the toolchain located at: openwrt/staging_dir/toolchain-mips_34kc_gcc-4.8-linaro_uClibc-
I've also tried to compile the software with mips-openwrt-linux-g++.
Now another error is given:
mips-openwrt-linux-g++ -shared -fPIC -o ../bin/mips-openwrt-linux-g++/ #"filelist.txt" -L. -lpthread -lrt -O3
openwrt/staging_dir/toolchain-mips_34kc_gcc-4.8-linaro_uClibc- ../temp/mips-openwrt-linux/sys_snap_msgsock.o: relocation R_MIPS_26 against `close' can not be used when making a shared object; recompile with -fPIC
../temp/mips-openwrt-linux/sys_snap_msgsock.o: could not read symbols: Bad value
collect2: error: ld returned 1 exit status
make: *** [../bin/mips-openwrt-linux-g++/] Error 1
I hope someone is familiar with this error and can help me out.
Thanks in advance.
There are some pre-compiled binaries. In the makefiles i changed the CC to my g++ directory. There is no LD flag so i cannot set my linker over there.
Can you cross compile and run a "hello world" program?
What is the output of file ../temp/mips-openwrt-linux/sys_snap_msgsock.o?

create position independent object file from LLVM bit code

I have a llvm module that i've dumped as bitcode file with llvm::WriteBitcodeToFile. I want to turn this bitcode file into an native dynamically loadable library that contains the functions in the module.
How do i do this? i tried using llc for this, but this produces code that apparently is not relocatable, since after doing the following steps:
llc -enable-pie -cppgen=functions -filetype=asm executableModule -o em.s
then, assemblying with gnu as into an object file:
as -o mylib.o em.s
finally, trying to produce a shared library with:
gcc -shared -o -fPIC mylib.o
fails with the error:
/usr/bin/ld: error: mylib.o: requires dynamic R_X86_64_PC32 reloc against '' which may overflow at runtime; recompile with -fPIC
collect2: ld returned 1 exit status
You need to setup relocation model. Something like -llc -relocation-model=pic. Do not use PIE, because it's for executables, not for libraries. Also, -cppgen does not make any sense here, it's for cpp backend only.