Fun with platform linker inconsistencies (AIX vs. Linux)

Imagine we have three source files, to be built into a pair of shared libs (one with a dependency on the other) and an exe as in:

// s1.C
extern "C" void foo(void){}

// s2.C
extern "C" void foo(void) ;
extern "C" void bar(void){foo();}

// m.C
extern "C" void foo(void) ;
extern "C" void bar(void) ;

int main()
{
   bar() ;
   foo() ;
   return 0 ;
}

On Linux, we can compile and link these with command line of the following sort

# g++ -shared s1.C -o libs1.so -fpic
# g++ -shared s2.C -o libs2.so -fpic -L. -ls1
# g++ -L. -ls2 m.C -Wl,-rpath-link,`pwd` -Wl,-rpath,`pwd`

Notice that we’ve not explicitly linked to libs1.so on Linux, even though we are using a symbol from it explictly. The linker picks up dependencies from other things that you choose to link to.

On AIX the equivalent commands to create a pair of shared libraries and link the exe to it fails at that exe link

# xlC -q64 -qmkshrobj s1.C -o shr1.o
# ar -X64 -crv libs1.a shr1.o
# xlC -q64 -qmkshrobj s2.C -o shr2.o -L. -ls1
# ar -X64 -crv libs2.a shr2.o
# xlC -q64 -L. -ls2 m.C
ld: 0711-317 ERROR: Undefined symbol: .foo
ld: 0711-345 Use the -bloadmap or -bnoquiet option to obtain more information.

You’ve got to add -ls1 to those link flags to get the exe to find its dependencies. I wonder which of these two link time behaviours is more common?

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