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
The problem with g++ -o myApp -lfoo -lbar -lfoo is that there is no guarantee, that two passes over libfoo and one pass over libbar are enough. The approach with Wl,–start-group … -Wl,–end-group is better, because more robust. Consider the following scenario (all symbols are in different object-files): myApp needs symbol fooA defined in libfoo. … Read more
You’ll need to pass the -static to the linker, but only for particular libraries you want. e.g.: g++ -o main main.cpp -Wl,-Bstatic -lmath -Wl,-Bdynamic
key function is defined as the first non-inline, virtual function declared in the class. The official gcc wiki about it is here.
global directive is NASM specific. It is for exporting symbols in your code to where it points in the object code generated. Here you mark _start symbol global so its name is added in the object code (a.o). The linker (ld) can read that symbol in the object code and its value so it knows … Read more
ar In Linux, ar is the GNU general purpose archiver. (There are non-GNU variants of ar in other Unix-like OSes). With the option c ar c… archive-name file… It creates an archive containing copies of file…. The archive-name conventionally but not necessarily has the extension .a (for archive). Each file… may be any kind of … Read more
From man gcc: -Xlinker option Pass option as an option to the linker. You can use this to supply system-specific linker options which GCC does not know how to recognize. If you want to pass an option that takes a separate argument, you must use -Xlinker twice, once for the option and once for the … Read more
I am able to reproduce this on an Ubuntu 10.10 system (GNU ld (GNU Binutils for Ubuntu) 2.20.51-system.20100908), and I think I have your answer. First, some methodology. After confirming this happens to me in a small VM (512MB ram, 2GB swap), from here I decided the easiest thing to do would be to strace … Read more
Use –whole-archive linker option. Libraries that come after it in the command line will not have unreferenced symbols discarded. You can resume normal linking behaviour by adding –no-whole-archive after these libraries. In your example, the command will be: g++ -o program main.o -Wl,–whole-archive /path/to/libmylib.a In general, it will be: g++ -o program main.o \ -Wl,–whole-archive … Read more
Why is it, that ld MUST be able to locate liba.so when linking test? Because to me it doesn’t seem like ld is doing much else than confirming liba.so‘s existence. For instance, running readelf –dynamic ./test only lists libb.so as needed, so I guess the dynamic linker must discover the libb.so -> liba.so dependency on … Read more