First, you should generally use -fPIC flag when building shared libraries. Not using it “works” on 32-bit Linux, but would fail on 64-bit one with an error similar to: /usr/bin/ld: /tmp/ccUUrz9c.o: relocation R_X86_64_32 against `.rodata’ can not be used when making a shared object; recompile with -fPIC Second, your program will work as you expect … Read more
The dynamic linker actually searches several places to find each dynamic library. These include (from man ld.so): Paths given by the environment variable LD_LIBRARY_PATH Paths baked into the binary load the library under the DT_RUNPATH entry The cache file /etc/ld.so.cache /lib and /usr/lib If you want to get the path for a specific shared library, … Read more
That’s bug no 961964 of MATLAB known since R2012b (8.0). MATLAB dynamically loads some libs with static TLS (thread local storage, e.g. see gcc compiler flag -ftls-model). Loading too many such libs => no space left. Until now mathwork’s only workaround is to load the important(!) libs first by using them early (they suggest to … Read more
I needed a solution to this because I have a scriptable system that has no filesystem (using blobs from a database) and needs to load binary plugins to support some scripts. This is the solution I came up with which works on FreeBSD but may not be portable. void *dlblob(const void *blob, size_t len) { … Read more
In Linux/ELF you can pass the -export-dynamic option to the linker (-rdynamic on the compiler driver gcc) so symbols from the executable are exported to shared objects. You’d have a dummy print implementation in your library, which would be shadowed by the implementation on your executable, since the executable is usually searched before shared objects … Read more
You can define an on-load function for a linux library using the .init mechanism. This is the same as specifying the load-time entry point for a binary (e.g. using something other than main as the entry point for a program). When linking using ld directly you use the: -init <function name> or if you’re using … Read more
Update 2: see Andrew G Morgan’s slightly more complicated solution which does work for any GLIBC (that solution is also used in libc.so.6 itself (since forever), which is why you can run it as ./libc.so.6 (it prints version info when invoked that way)). Update 1: this no longer works with newer GLIBC versions: ./a.out: error … Read more