Yes, you should recompile OCaml with -fPIC. I ran into the same problem a
few months ago, and noticed this bit of information in the INSTALL file:

  On a Linux x86/64 bits host, to build the run-time system in PIC mode
  (enables putting the runtime in a shared library,
   at a small performance cost):
    ./configure -cc "gcc -fPIC" -aspp "gcc -c -fPIC"


On Wed, Nov 30, 2011 at 1:37 PM, Alex Rubinsteyn
<alex.rubinsteyn@gmail.com>wrote:

> Hi,
>
> I'd like to package up some OCaml code (along with C bindings) as a shared
> library. However, I'm encountering the following linker error:
>
> /usr/bin/ld: /usr/lib/ocaml/libasmrun.a(startup.o): relocation R_X86_64_32
> against `.rodata.str1.1' can not be used when making a shared object;
> recompile with -fPIC
> /usr/lib/ocaml/libasmrun.a: could not read symbols: Bad value
>
> Do I have to recompile OCaml with -fPIC to put the runtime inside a shared
> library?
>
>
>