Linux Shared Library (DLL) & -rpath,'$ORIGIN'
The Argument -rpath,'$ORIGIN'Needs to be prefixed with "-Wl," for most Linux OS (or "-R<path>" for Solaris, -brtl for AIX and "-Wl,+b<path>" for HPUX). It is to pass linker options to your linker through gcc or g++. It is significant if you need to build a binary that depends on other dynamic library. "rpath" means runtime path (to load dependent dynamic library). And the very useful variable that we frequently used is "$ORIGIN" which means the path where your (link) target binary is loaded.
# assuming your target lib is libb.so and it depends on liba.so# and their deployment structure is like:<install_root>|libb.so|<sub_dir>|liba.so# then you should supply below argument to your gcc or g++:# the double '$' is necessary if it is written in makefile (as escaping char)# -Wl,-rpath,'$$ORIGIN/<sub_dir>'# or, without single quote, you can write it like:# -Wl,-rpath,\$$ORIGIN/<sub_dir># and -shared and -fPIC is usually need to build dynamic linkable librarygcc -o libb.so -shared -fPIC -L. -la -Wl,-rpath,\$$ORIGIN/<sub_dir> libb.c
Check RPATH with 'readelf':
# -d means dynamicreadelf -d <dll_name># output looks like:#Tag Type Name/Value# 0x0000000000000001 (NEEDED) Shared library: # 0x0000000000000001 (NEEDED) Shared library: # 0x0000000000000001 (NEEDED) Shared library: # 0x0000000000000001 (NEEDED) Shared library: # 0x0000000000000001 (NEEDED) Shared library: # 0x000000000000000f (RPATH) Library rpath: [$ORIGIN/libb]# 0x000000000000000c (INIT) 0x7d8# 0x000000000000000d (FINI) 0xa88# 0x000000006ffffef5 (GNU_HASH) 0x158# 0x0000000000000005 (STRTAB) 0x3c8# 0x0000000000000006 (SYMTAB) 0x1a0# 0x000000000000000a (STRSZ) 479 (bytes)# 0x000000000000000b (SYMENT) 24 (bytes)# 0x0000000000000003 (PLTGOT) 0x200e28# 0x0000000000000002 (PLTRELSZ) 216 (bytes)# 0x0000000000000014 (PLTREL) RELA# 0x0000000000000017 (JMPREL) 0x700# 0x0000000000000007 (RELA) 0x628# 0x0000000000000008 (RELASZ) 216 (bytes)# 0x0000000000000009 (RELAENT) 24 (bytes)# 0x000000006ffffffe (VERNEED) 0x5d8# 0x000000006fffffff (VERNEEDNUM) 2# 0x000000006ffffff0 (VERSYM) 0x5a8# 0x000000006ffffff9 (RELACOUNT) 3# 0x0000000000000000 (NULL) 0x0
Sample
// liba.h#ifndef LIBA_GPGH7YWD_H#define LIBA_GPGH7YWD_Hnamespace dlltest {void foo();class A {public: A();};} /* dlltest */#endif /* end of include guard: LIBA_GPGH7YWD_H */// liba.cpp#include <iostream>#include "liba.h"namespace dlltest {void foo() { std::cout << "liba:foo" << std::endl;}A::A() { foo();}}// libb.h#ifndef LIBB_5NC56UVQ_H#define LIBB_5NC56UVQ_H#include "liba.h"namespace dlltest {void goo();class B : public A {public: B();};}#endif /* end of include guard: LIBB_5NC56UVQ_H */// libb.cpp#include <iostream>#include "libb.h"namespace dlltest {void goo() { std::cout << "libb:goo" << std::endl;}B::B() { goo();}}// libc1.h: // you never want to name it libc.so because it is // the name of standard C library#ifndef LIBC_1Y6MU09S_H#define LIBC_1Y6MU09S_H#include "libb.h"extern "C" void hoo();extern "C" void hoo2();namespace dlltest {class C : public B {public: C();};}#endif /* end of include guard: LIBC_1Y6MU09S_H */// libc1.cpp#include <iostream>#include "libc1.h"void hoo() { std::cout << "libc:hoo" << std::endl;}void hoo2() { dlltest::C c;}namespace dlltest {C::C() { hoo();}}
// main.cpp// implicit dll dependency#include "libc1.h"using namespace dlltest;int main(int argc, const char *argv[]){ C c; return 0;}
// main2.cpp// load dll with dlopen#include <stdio.h>#include <stdlib.h>#include <dlfcn.h>typedef void(*FP)();int main(int argc, char **argv) {void *handle;char *error;handle = dlopen ("./libc1.so", RTLD_LAZY);if (!handle) { fprintf (stderr, "%s\n", dlerror()); exit(1);}dlerror(); /* Clear any existing error */FP fp = (FP)dlsym(handle, "hoo2");if ((error = dlerror()) != NULL){ fprintf (stderr, "%s\n", error); exit(1);}(*fp)();dlclose(handle);return 0;}
// makefile# Dynamic loading shared library# dynamic libraries could be independent on each other when built# but, in this case, executable binary depends on all of themdll: dir g++ -fPIC -shared -o bin/liba.so liba.cpp g++ -fPIC -shared -o bin/libb.so libb.cpp g++ -fPIC -shared -o bin/libc1.so libc1.cpp g++ -o bin/dlink main.cpp -Lbin -lc1 -lb -la -Wl,-rpath,\$$ORIGIN# libc1.so is loaded by dlopen in main2.cpp# libc1.so implicitly depends on libb.so, without RPATH libc1 # doesn't know where to find it# libb.so implicitly depends on liba.so, without RPATH libb doesn't # know where to find it# need to link libb.so and liba.so to demo, so demo will load libb# and liba when it needs themdlopen: dir2 g++ -fPIC -shared -o bin/liba.so liba.cpp g++ -fPIC -shared -o bin/libb/libb.so libb.cpp g++ -fPIC -shared -o bin/libc1.so libc1.cpp g++ -o bin/dldemo main2.cpp -Lbin/libb -Lbin -la -lb -ldl -Wl,-rpath,\$$ORIGIN -Wl,-rpath,\$$ORIGIN/libb# alternative to dlopen case:# add libb dependency explicitly when build libc1:# -Lbin/libb and -lb is essential because you want libc1 know libb# has the symbols it needs and -rpath tells libc1 where to find libb# but liba's search path is not built into libb, it's needed to # build the dependency into dldemo# otherwise,update the rpath of libb(for liba) should also work, check dlopen3dlopen2: dir2 g++ -fPIC -shared -o bin/liba.so liba.cpp g++ -fPIC -shared -o bin/libb/libb.so libb.cpp g++ -fPIC -shared -o bin/libc1.so libc1.cpp -Lbin/libb -lb -Wl,-rpath,\$$ORIGIN/libb g++ -o bin/dldemo main2.cpp -Lbin -la -ldl -Wl,-rpath,\$$ORIGIN# second alternative to dlopen case:# dldemo implicitly depends on none of 3 libs, but you still need to tell it where to# find libc1 with -rpath. otherwise, if you specify correct path to libc1.so when # dlopen (and start the program in correct working diretory if you use indirect # file path in dlopen), then -rpath is not needed # libc1 implicitly depends on libb and libc1 know where to find libb with -rpath setup# libb implicitly depends on liba and libb know where to find liba with -rpath setupdlopen3: dir2 g++ -fPIC -shared -o bin/liba.so liba.cpp g++ -fPIC -shared -o bin/libb/libb.so libb.cpp -Lbin -la -Wl,-rpath,\$$ORIGIN/.. g++ -fPIC -shared -o bin/libc1.so libc1.cpp -Lbin/libb -lb -Wl,-rpath,\$$ORIGIN/libb #g++ -o bin/dldemo main2.cpp -ldl -Wl,-rpath,\$$ORIGIN g++ -o bin/dldemo main2.cpp -ldl# demostrate how to use -rpath to organize libraries into separate foldersstrc1: dir2 g++ -fPIC -shared -o bin/liba.so liba.cpp g++ -fPIC -shared -o bin/libb/libb.so libb.cpp g++ -fPIC -shared -o bin/libc1.so libc1.cpp g++ -o bin/strc1 main.cpp -Lbin -lc1 -la -Lbin/libb -lb \ -Wl,-rpath,\$$ORIGIN -Wl,-rpath,\$$ORIGIN/libb# mix static lib with dynamic libmix1: dir g++ -fPIC -shared -o bin/liba.so liba.cpp g++ -fPIC -c libb.cpp g++ -fPIC -shared -o bin/libc1.so libc1.cpp libb.o g++ -o bin/mix1 main.cpp -Lbin -lc1 -la -Wl,-rpath,\$$ORIGIN rm *.o# static link:# if you build 'dll' before 'mix2' without clean, you can find the below -lc1# will link dynamic lib libc1.so instead of static lib libc1.a# the conclusion is shared lib link is default behaviormix2: dir clean g++ -fPIC -shared -o bin/liba.so liba.cpp g++ -fPIC -shared -o bin/libb.so libb.cpp g++ -c libc1.cpp ar -cvq bin/libc1.a libc1.o g++ -o bin/mix2 main.cpp -Lbin -lc1 -lb -la -Wl,-rpath,\$$ORIGIN rm *.odir: if [ ! -d bin ]; then mkdir bin; fidir2: if [ ! -d bin/libb ]; then mkdir -p bin/libb; ficlean: rm -rf bin/*
For more information:
[*]check 'man ld'
[*]RPATH on Wiki
[*]Shared Library Search Path
[*]use ldd command to check dependency of a binary
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