This directory contains support code for the Squeak FFI (foreign
function interface) primitives.  You should not even be here reading
this unless (i) the configure script refuses to include FFI support in
your build, or (ii) you want to try to make your FFI calls go lots
faster by avoiding the use of libffi.

About the FFI primitives
------------------------

Squeak can dynamically construct callouts to C code at runtime via one
of two mechanisms, `apicall' and `cdecl'.  The `cdecl' method
constructs a `call interface description' (a data structure
representing a function's signature) which is used by libffi [1] to
construct and invoke a call to the foreign function.  This method is
portable but horribly slow.  The `apicall' method constructs a stack
frame on-the-fly which is used to invoke the foreign function
directly.

The `apicall' method is MUCH faster than `cdecl' (more than FOUR times
faster) but relies on horribly platform-dependent code.

Support for the `apicall' method is now available for a few platforms
on Unix:

  - PowerPC and x86 using the SVr4 ABI (found on most GNU/Linux and
    BSD-like systems, with the notable exception of Darwin/MacOSX)

  - PowerPC using the Darwin ABI (similar to Mach)

Testing your FFI support
------------------------

First run the script `ffi-test-config' (no arguments) which will look
to see if your platform has support for the `apicall' method.  If it
prints `any-libffi' then you must either install libffi [1] before you
can use the FFI primitives or implement the missing support [2].  If
it prints anything else then it has found what it thinks is suitable
support for your platform [3].

To run the test suite, just type `make' [4].  This will build a program
called `main' that tries quite hard to break the FFI support code.  If
it fails using the built-in support code then you've found a bug in
either the support code or the test code [5].  If you want to try
again with libffi, then type:

	make clean
	make CPU=any ABI=libffi LIB=-lffi
	./main

If it fails again you've found a bug either in libffi (send bug
reports to the relevant mailing list, not me) or in the test code.

To tidy up afterwards, type `make clean'.

Notes
-----

[1] libffi is now part of gcc.  If you need to install it, download
    just the contents of the top-level `gcc' directory and the
    `libffi' subdirectory.  Then `cd' to `libffi' and type:

	./configure
	make
	sudo make install

    If it breaks, you get to keep the pieces.


[2] Figure out your canonical cpu and abi (os) name.  Write a bunch of
    C code to create a stack frame in `${cpu}-${abi}.c' and the
    assembler `trampoline' that pused it and jumps to the destination
    function in the file `${cpu}-${abi}-asm.S'.  This will allow the
    configure script to find and use your support.
    
[3] If it doesn't find support code for your platform and you think it
    should (based on the cpu-abi variants available) then add your
    canonical host/os names to the tests in ffi-test-config.  If the
    resulting program works, make similar changes in `acinclude.m4' so
    that the support is included in the Squeak VM.  Then mail the
    modified files to me [5].

[4] By default the Makefile will try to figure this out for itself
    using rules similar to those in the configure script.  You must be
    using GNU make for this to work.

[5] Send bug reports and support code for new platforms to:
	ian.piumarta@squeakland.org
