FFI question

Ian Piumarta ian.piumarta at inria.fr
Mon May 3 15:25:01 UTC 2004

On 03 May 2004, at 07:23, liste..squeak wrote:

> I have written a C++
> shared library and when I attempt to use it in squeak with
> FFI, I have the classical "Error : can't find function adress".
> Do you know whether it is possible to use C++ librarries with
> FFI in the same way that I can use C libraries ?

Are you taking into account the name mangling that C++ will perform on 
your function identifiers?

E.g., 'int foo(int)' will typically be associated with a symbol not 
entirely unlike '__Z3fooi', and you must supply this mangled name to 
the FFI rather than simply 'foo'.

If you have 'nm' then run it on your .o files to see the symbols that 
it really contains.  If you have 'c++filt' you can also pipe the output 
from 'nm' into it to obtain the original human-readable prototypes.  
(Some versions of 'nm' have an option to demangle the symbols 
implicitly before displaying them.)

Beware that different compilers (or even different versions of the same 
compiler) will mangle names differently.  There is no easy, portable 
way to predict how an indentifier might be mangled during compilation.  
Your code will likely not run on two different platforms (or the same 
platform with two different compilers).  For example, you might have 
several versions of c++filt (with numeric suffixes denoting different 
versions of the mangling scheme that each of them recognises).

Another approach would be to turn off mangling explicitly for all 
functions that you want to export to the FFI.  Declare their prototypes 
up-front inside an 'extern "C" { ... }' section, before defining them.  
This would be far more portable than attempting to predict how the C++ 
compiler will mangle your symbols.


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