re PR libffi/41908 (closures fail for some structure arguments containing floats)

[gcc.git] / libffi / README

This directory contains the libffi package, which is not part of GCC but
shipped with GCC as convenience.

Status
======

libffi-3.0.8 was released on December 19, 2008. Check the libffi web
page for updates: <URL:http://sourceware.org/libffi/>.


What is libffi?
===============

Compilers for high level languages generate code that follow certain
conventions. These conventions are necessary, in part, for separate
compilation to work. One such convention is the "calling
convention". The "calling convention" is essentially a set of
assumptions made by the compiler about where function arguments will
be found on entry to a function. A "calling convention" also specifies
where the return value for a function is found.

Some programs may not know at the time of compilation what arguments
are to be passed to a function. For instance, an interpreter may be
told at run-time about the number and types of arguments used to call
a given function. Libffi can be used in such programs to provide a
bridge from the interpreter program to compiled code.

The libffi library provides a portable, high level programming
interface to various calling conventions. This allows a programmer to
call any function specified by a call interface description at run
time.  

FFI stands for Foreign Function Interface.  A foreign function
interface is the popular name for the interface that allows code
written in one language to call code written in another language. The
libffi library really only provides the lowest, machine dependent
layer of a fully featured foreign function interface. A layer must
exist above libffi that handles type conversions for values passed
between the two languages.


Supported Platforms
===================

Libffi has been ported to many different platforms, although this
release was only tested on:

     arm oabi linux
     arm eabi linux
     hppa linux
     mips o32 linux (little endian)
     powerpc darwin
     powerpc freebsd
     powerpc64 linux
     sparc solaris
     sparc64 freebsd
     sparc64 solaris
     x86 cygwin
     x86 darwin
     x86 freebsd
     x86 linux
     x86 openbsd
     x86 solaris
     x86-64 mingw
     x86-64 darwin
     x86-64 linux
     x86-64 OS X
     x86-64 freebsd
     x86-64 solaris
     
Please send additional platform test results to
libffi-discuss@sourceware.org.

Installing libffi
=================

[Note: before actually performing any of these installation steps,
 you may wish to read the "Platform Specific Notes" below.]

First you must configure the distribution for your particular
system. Go to the directory you wish to build libffi in and run the
"configure" program found in the root directory of the libffi source
distribution.

You may want to tell configure where to install the libffi library and
header files. To do that, use the --prefix configure switch.  Libffi
will install under /usr/local by default. 

If you want to enable extra run-time debugging checks use the the
--enable-debug configure switch. This is useful when your program dies
mysteriously while using libffi. 

Another useful configure switch is --enable-purify-safety. Using this
will add some extra code which will suppress certain warnings when you
are using Purify with libffi. Only use this switch when using 
Purify, as it will slow down the library.

Configure has many other options. Use "configure --help" to see them all.

Once configure has finished, type "make". Note that you must be using
GNU make.  You can ftp GNU make from prep.ai.mit.edu:/pub/gnu.

To ensure that libffi is working as advertised, type "make check".
This will require that you have DejaGNU installed.

To install the library and header files, type "make install".


Platform Specific Notes
=======================

	MIPS - Irix 5.3 & 6.x
	---------------------

Irix 6.2 and better supports three different calling conventions: o32,
n32 and n64. Currently, libffi only supports both o32 and n32 under
Irix 6.x, but only o32 under Irix 5.3. Libffi will automatically be
configured for whichever calling convention it was built for.

By default, the configure script will try to build libffi with the GNU
development tools. To build libffi with the SGI development tools, set
the environment variable CC to either "cc -32" or "cc -n32" before
running configure under Irix 6.x (depending on whether you want an o32
or n32 library), or just "cc" for Irix 5.3.

With the n32 calling convention, when returning structures smaller
than 16 bytes, be sure to provide an RVALUE that is 8 byte aligned.
Here's one way of forcing this:

	double struct_storage[2];
	my_small_struct *s = (my_small_struct *) struct_storage;  
	/* Use s for RVALUE */

If you don't do this you are liable to get spurious bus errors. 

"long long" values are not supported yet.

You must use GNU Make to build libffi on SGI platforms.


	PowerPC System V ABI
	--------------------

There are two `System V ABI's which libffi implements for PowerPC.
They differ only in how small structures are returned from functions.

In the FFI_SYSV version, structures that are 8 bytes or smaller are
returned in registers.  This is what GCC does when it is configured
for solaris, and is what the System V ABI I have (dated September
1995) says.

In the FFI_GCC_SYSV version, all structures are returned the same way:
by passing a pointer as the first argument to the function.  This is
what GCC does when it is configured for linux or a generic sysv
target.

EGCS 1.0.1 (and probably other versions of EGCS/GCC) also has a
inconsistency with the SysV ABI: When a procedure is called with many
floating-point arguments, some of them get put on the stack.  They are
all supposed to be stored in double-precision format, even if they are
only single-precision, but EGCS stores single-precision arguments as
single-precision anyway.  This causes one test to fail (the `many
arguments' test).


History
=======

3.0.7 Nov-11-08
        Fix for ppc FreeBSD.
	(thanks to Andreas Tobler)

3.0.6 Jul-17-08
        Fix for closures on sh.
	Mark the sh/sh64 stack as non-executable.
	(both thanks to Kaz Kojima)

3.0.5 Apr-3-08
        Fix libffi.pc file.
	Fix #define ARM for IcedTea users.
	Fix x86 closure bug.

3.0.4 Feb-24-08
        Fix x86 OpenBSD configury.

3.0.3 Feb-22-08
        Enable x86 OpenBSD thanks to Thomas Heller, and
	x86-64 FreeBSD thanks to Björn König and Andreas Tobler.
	Clean up test instruction in README.

3.0.2 Feb-21-08
        Improved x86 FreeBSD support.
	Thanks to Björn König.

3.0.1 Feb-15-08
        Fix instruction cache flushing bug on MIPS.
	Thanks to David Daney.

3.0.0 Feb-15-08
        Many changes, mostly thanks to the GCC project.
	Cygnus Solutions is now Red Hat.

  [10 years go by...]

1.20 Oct-5-98
	Raffaele Sena produces ARM port.

1.19 Oct-5-98
	Fixed x86 long double and long long return support.
	m68k bug fixes from Andreas Schwab.
	Patch for DU assembler compatibility for the Alpha from Richard
	Henderson.

1.18 Apr-17-98
	Bug fixes and MIPS configuration changes.

1.17 Feb-24-98
	Bug fixes and m68k port from Andreas Schwab. PowerPC port from
	Geoffrey Keating. Various bug x86, Sparc and MIPS bug fixes.

1.16 Feb-11-98
	Richard Henderson produces Alpha port.

1.15 Dec-4-97
	Fixed an n32 ABI bug. New libtool, auto* support.

1.14 May-13-97
	libtool is now used to generate shared and static libraries.
	Fixed a minor portability problem reported by Russ McManus
	<mcmanr@eq.gs.com>.

1.13 Dec-2-96
	Added --enable-purify-safety to keep Purify from complaining
	about certain low level code.
	Sparc fix for calling functions with < 6 args.
	Linux x86 a.out fix.

1.12 Nov-22-96
	Added missing ffi_type_void, needed for supporting void return 
	types. Fixed test case for non MIPS machines. Cygnus Support 
	is now Cygnus Solutions. 

1.11 Oct-30-96
	Added notes about GNU make.

1.10 Oct-29-96
	Added configuration fix for non GNU compilers.

1.09 Oct-29-96
	Added --enable-debug configure switch. Clean-ups based on LCLint 
	feedback. ffi_mips.h is always installed. Many configuration 
	fixes. Fixed ffitest.c for sparc builds.

1.08 Oct-15-96
	Fixed n32 problem. Many clean-ups.

1.07 Oct-14-96
	Gordon Irlam rewrites v8.S again. Bug fixes.

1.06 Oct-14-96
	Gordon Irlam improved the sparc port. 

1.05 Oct-14-96
	Interface changes based on feedback.

1.04 Oct-11-96
	Sparc port complete (modulo struct passing bug).

1.03 Oct-10-96
	Passing struct args, and returning struct values works for
	all architectures/calling conventions. Expanded tests.

1.02 Oct-9-96
	Added SGI n32 support. Fixed bugs in both o32 and Linux support.
	Added "make test".

1.01 Oct-8-96
	Fixed float passing bug in mips version. Restructured some
	of the code. Builds cleanly with SGI tools.

1.00 Oct-7-96
	First release. No public announcement.


Authors & Credits
=================

libffi was originally written by Anthony Green <green@redhat.com>.

The developers of the GNU Compiler Collection project have made
innumerable valuable contributions.  See the ChangeLog file for
details.

Some of the ideas behind libffi were inspired by Gianni Mariani's free
gencall library for Silicon Graphics machines.

The closure mechanism was designed and implemented by Kresten Krab
Thorup.

Major processor architecture ports were contributed by the following
developers:

alpha		Richard Henderson
arm		Raffaele Sena
cris		Simon Posnjak, Hans-Peter Nilsson
frv		Anthony Green
ia64		Hans Boehm
m32r		Kazuhiro Inaoka
m68k		Andreas Schwab
mips		Anthony Green, Casey Marshall
mips64		David Daney
pa		Randolph Chung, Dave Anglin, Andreas Tobler
powerpc		Geoffrey Keating, Andreas Tobler, 
			 David Edelsohn, John Hornkvist
powerpc64	Jakub Jelinek
s390		Gerhard Tonn, Ulrich Weigand
sh		Kaz Kojima
sh64		Kaz Kojima
sparc		Anthony Green, Gordon Irlam
x86		Anthony Green, Jon Beniston
x86-64		Bo Thorsen

Jesper Skov and Andrew Haley both did more than their fair share of
stepping through the code and tracking down bugs.

Thanks also to Tom Tromey for bug fixes, documentation and
configuration help.

Thanks to Jim Blandy, who provided some useful feedback on the libffi
interface.

Andreas Tobler has done a tremendous amount of work on the testsuite.

Alex Oliva solved the executable page problem for SElinux.

The list above is almost certainly incomplete and inaccurate.  I'm
happy to make corrections or additions upon request.

If you have a problem, or have found a bug, please send a note to
green@redhat.com.