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/Modules/_ctypes/libffi_osx/README

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  1This directory contains the libffi package, which is not part of GCC but
  2shipped with GCC as convenience.
  3
  4Status
  5======
  6
  7libffi-2.00 has not been released yet! This is a development snapshot!
  8
  9libffi-1.20 was released on October 5, 1998. Check the libffi web
 10page for updates: <URL:http://sources.redhat.com/libffi/>.
 11
 12
 13What is libffi?
 14===============
 15
 16Compilers for high level languages generate code that follow certain
 17conventions. These conventions are necessary, in part, for separate
 18compilation to work. One such convention is the "calling
 19convention". The "calling convention" is essentially a set of
 20assumptions made by the compiler about where function arguments will
 21be found on entry to a function. A "calling convention" also specifies
 22where the return value for a function is found.
 23
 24Some programs may not know at the time of compilation what arguments
 25are to be passed to a function. For instance, an interpreter may be
 26told at run-time about the number and types of arguments used to call
 27a given function. Libffi can be used in such programs to provide a
 28bridge from the interpreter program to compiled code.
 29
 30The libffi library provides a portable, high level programming
 31interface to various calling conventions. This allows a programmer to
 32call any function specified by a call interface description at run
 33time.  
 34
 35Ffi stands for Foreign Function Interface. A foreign function
 36interface is the popular name for the interface that allows code
 37written in one language to call code written in another language. The
 38libffi library really only provides the lowest, machine dependent
 39layer of a fully featured foreign function interface. A layer must
 40exist above libffi that handles type conversions for values passed
 41between the two languages.
 42
 43
 44Supported Platforms and Prerequisites
 45=====================================
 46
 47Libffi has been ported to:
 48
 49	SunOS 4.1.3 & Solaris 2.x (SPARC-V8, SPARC-V9)
 50
 51	Irix 5.3 & 6.2 (System V/o32 & n32)
 52
 53	Intel x86 - Linux (System V ABI)
 54
 55	Alpha - Linux and OSF/1
 56
 57	m68k - Linux (System V ABI)
 58
 59	PowerPC - Linux (System V ABI, Darwin, AIX)
 60
 61	ARM - Linux (System V ABI)
 62
 63Libffi has been tested with the egcs 1.0.2 gcc compiler. Chances are
 64that other versions will work.  Libffi has also been built and tested
 65with the SGI compiler tools.
 66
 67On PowerPC, the tests failed (see the note below).
 68
 69You must use GNU make to build libffi. SGI's make will not work.
 70Sun's probably won't either.
 71	
 72If you port libffi to another platform, please let me know! I assume
 73that some will be easy (x86 NetBSD), and others will be more difficult
 74(HP).
 75
 76
 77Installing libffi
 78=================
 79
 80[Note: before actually performing any of these installation steps,
 81 you may wish to read the "Platform Specific Notes" below.]
 82
 83First you must configure the distribution for your particular
 84system. Go to the directory you wish to build libffi in and run the
 85"configure" program found in the root directory of the libffi source
 86distribution.
 87
 88You may want to tell configure where to install the libffi library and
 89header files. To do that, use the --prefix configure switch.  Libffi
 90will install under /usr/local by default. 
 91
 92If you want to enable extra run-time debugging checks use the the
 93--enable-debug configure switch. This is useful when your program dies
 94mysteriously while using libffi. 
 95
 96Another useful configure switch is --enable-purify-safety. Using this
 97will add some extra code which will suppress certain warnings when you
 98are using Purify with libffi. Only use this switch when using 
 99Purify, as it will slow down the library.
100
101Configure has many other options. Use "configure --help" to see them all.
102
103Once configure has finished, type "make". Note that you must be using
104GNU make. SGI's make will not work.  Sun's probably won't either.
105You can ftp GNU make from prep.ai.mit.edu:/pub/gnu.
106
107To ensure that libffi is working as advertised, type "make test".
108
109To install the library and header files, type "make install".
110
111
112Using libffi
113============
114
115	The Basics
116	----------
117
118Libffi assumes that you have a pointer to the function you wish to
119call and that you know the number and types of arguments to pass it,
120as well as the return type of the function.
121
122The first thing you must do is create an ffi_cif object that matches
123the signature of the function you wish to call. The cif in ffi_cif
124stands for Call InterFace. To prepare a call interface object, use the
125following function:
126
127ffi_status ffi_prep_cif(ffi_cif *cif, ffi_abi abi,
128			unsigned int nargs, 
129			ffi_type *rtype, ffi_type **atypes);
130
131	CIF is a pointer to the call interface object you wish
132		to initialize.
133
134	ABI is an enum that specifies the calling convention 
135		to use for the call. FFI_DEFAULT_ABI defaults
136		to the system's native calling convention. Other
137		ABI's may be used with care. They are system
138		specific.
139
140	NARGS is the number of arguments this function accepts.	
141		libffi does not yet support vararg functions.
142
143	RTYPE is a pointer to an ffi_type structure that represents
144		the return type of the function. Ffi_type objects
145		describe the types of values. libffi provides
146		ffi_type objects for many of the native C types:
147		signed int, unsigned int, signed char, unsigned char,
148		etc. There is also a pointer ffi_type object and
149		a void ffi_type. Use &ffi_type_void for functions that 
150		don't return values.
151
152	ATYPES is a vector of ffi_type pointers. ARGS must be NARGS long.
153		If NARGS is 0, this is ignored.
154
155
156ffi_prep_cif will return a status code that you are responsible 
157for checking. It will be one of the following:
158
159	FFI_OK - All is good.
160
161	FFI_BAD_TYPEDEF - One of the ffi_type objects that ffi_prep_cif
162		came across is bad.
163
164
165Before making the call, the VALUES vector should be initialized 
166with pointers to the appropriate argument values.
167
168To call the the function using the initialized ffi_cif, use the
169ffi_call function:
170
171void ffi_call(ffi_cif *cif, void *fn, void *rvalue, void **avalues);
172
173	CIF is a pointer to the ffi_cif initialized specifically
174		for this function.
175
176	FN is a pointer to the function you want to call.
177
178	RVALUE is a pointer to a chunk of memory that is to hold the
179		result of the function call. Currently, it must be
180		at least one word in size (except for the n32 version
181		under Irix 6.x, which must be a pointer to an 8 byte 
182		aligned value (a long long). It must also be at least 
183		word aligned (depending on the return type, and the
184		system's alignment requirements). If RTYPE is 
185		&ffi_type_void, this is ignored. If RVALUE is NULL, 
186		the return value is discarded.
187
188	AVALUES is a vector of void* that point to the memory locations
189		holding the argument values for a call.
190		If NARGS is 0, this is ignored.
191
192
193If you are expecting a return value from FN it will have been stored
194at RVALUE.
195
196
197
198	An Example
199	----------
200
201Here is a trivial example that calls puts() a few times.
202
203    #include <stdio.h>
204    #include <ffi.h>
205    
206    int main()
207    {
208      ffi_cif cif;
209      ffi_type *args[1];
210      void *values[1];
211      char *s;
212      int rc;
213      
214      /* Initialize the argument info vectors */    
215      args[0] = &ffi_type_uint;
216      values[0] = &s;
217      
218      /* Initialize the cif */
219      if (ffi_prep_cif(&cif, FFI_DEFAULT_ABI, 1, 
220    		       &ffi_type_uint, args) == FFI_OK)
221        {
222          s = "Hello World!";
223          ffi_call(&cif, puts, &rc, values);
224          /* rc now holds the result of the call to puts */
225          
226          /* values holds a pointer to the function's arg, so to 
227	     call puts() again all we need to do is change the 
228             value of s */
229          s = "This is cool!";
230          ffi_call(&cif, puts, &rc, values);
231        }
232      
233      return 0;
234    }
235
236
237
238	Aggregate Types
239	---------------
240
241Although libffi has no special support for unions or bit-fields, it is
242perfectly happy passing structures back and forth. You must first
243describe the structure to libffi by creating a new ffi_type object
244for it. Here is the definition of ffi_type:
245
246    typedef struct _ffi_type
247    {
248      unsigned size;
249      short alignment;
250      short type;
251      struct _ffi_type **elements;
252    } ffi_type;
253    
254All structures must have type set to FFI_TYPE_STRUCT.  You may set
255size and alignment to 0. These will be calculated and reset to the
256appropriate values by ffi_prep_cif().
257
258elements is a NULL terminated array of pointers to ffi_type objects
259that describe the type of the structure elements. These may, in turn,
260be structure elements.
261
262The following example initializes a ffi_type object representing the
263tm struct from Linux's time.h:
264
265				    struct tm {
266					int tm_sec;
267					int tm_min;
268					int tm_hour;
269					int tm_mday;
270					int tm_mon;
271					int tm_year;
272					int tm_wday;
273					int tm_yday;
274					int tm_isdst;
275					/* Those are for future use. */
276					long int __tm_gmtoff__;
277					__const char *__tm_zone__;
278				    };
279
280    {
281      ffi_type tm_type;
282      ffi_type *tm_type_elements[12];
283      int i;
284
285      tm_type.size = tm_type.alignment = 0;
286      tm_type.elements = &tm_type_elements;
287    
288      for (i = 0; i < 9; i++)
289          tm_type_elements[i] = &ffi_type_sint;
290
291      tm_type_elements[9] = &ffi_type_slong;
292      tm_type_elements[10] = &ffi_type_pointer;
293      tm_type_elements[11] = NULL;
294
295      /* tm_type can now be used to represent tm argument types and
296	 return types for ffi_prep_cif() */
297    }
298
299
300
301Platform Specific Notes
302=======================
303
304	Intel x86
305	---------
306
307There are no known problems with the x86 port.
308
309	Sun SPARC - SunOS 4.1.3 & Solaris 2.x
310	-------------------------------------
311
312You must use GNU Make to build libffi on Sun platforms.
313
314	MIPS - Irix 5.3 & 6.x
315	---------------------
316
317Irix 6.2 and better supports three different calling conventions: o32,
318n32 and n64. Currently, libffi only supports both o32 and n32 under
319Irix 6.x, but only o32 under Irix 5.3. Libffi will automatically be
320configured for whichever calling convention it was built for.
321
322By default, the configure script will try to build libffi with the GNU
323development tools. To build libffi with the SGI development tools, set
324the environment variable CC to either "cc -32" or "cc -n32" before
325running configure under Irix 6.x (depending on whether you want an o32
326or n32 library), or just "cc" for Irix 5.3.
327
328With the n32 calling convention, when returning structures smaller
329than 16 bytes, be sure to provide an RVALUE that is 8 byte aligned.
330Here's one way of forcing this:
331
332	double struct_storage[2];
333	my_small_struct *s = (my_small_struct *) struct_storage;  
334	/* Use s for RVALUE */
335
336If you don't do this you are liable to get spurious bus errors. 
337
338"long long" values are not supported yet.
339
340You must use GNU Make to build libffi on SGI platforms.
341
342	ARM - System V ABI
343	------------------
344
345The ARM port was performed on a NetWinder running ARM Linux ELF
346(2.0.31) and gcc 2.8.1.
347
348
349
350	PowerPC System V ABI
351	--------------------
352
353There are two `System V ABI's which libffi implements for PowerPC.
354They differ only in how small structures are returned from functions.
355
356In the FFI_SYSV version, structures that are 8 bytes or smaller are
357returned in registers.  This is what GCC does when it is configured
358for solaris, and is what the System V ABI I have (dated September
3591995) says.
360
361In the FFI_GCC_SYSV version, all structures are returned the same way:
362by passing a pointer as the first argument to the function.  This is
363what GCC does when it is configured for linux or a generic sysv
364target.
365
366EGCS 1.0.1 (and probably other versions of EGCS/GCC) also has a
367inconsistency with the SysV ABI: When a procedure is called with many
368floating-point arguments, some of them get put on the stack.  They are
369all supposed to be stored in double-precision format, even if they are
370only single-precision, but EGCS stores single-precision arguments as
371single-precision anyway.  This causes one test to fail (the `many
372arguments' test).
373
374
375What's With The Crazy Comments?
376===============================
377
378You might notice a number of cryptic comments in the code, delimited
379by /*@ and @*/. These are annotations read by the program LCLint, a
380tool for statically checking C programs. You can read all about it at
381<http://larch-www.lcs.mit.edu:8001/larch/lclint/index.html>.
382
383
384History
385=======
386
3871.20 Oct-5-98
388	Raffaele Sena produces ARM port.
389
3901.19 Oct-5-98
391	Fixed x86 long double and long long return support.
392	m68k bug fixes from Andreas Schwab.
393	Patch for DU assembler compatibility for the Alpha from Richard
394	Henderson.
395
3961.18 Apr-17-98
397	Bug fixes and MIPS configuration changes.
398
3991.17 Feb-24-98
400	Bug fixes and m68k port from Andreas Schwab. PowerPC port from
401	Geoffrey Keating. Various bug x86, Sparc and MIPS bug fixes.
402
4031.16 Feb-11-98
404	Richard Henderson produces Alpha port.
405
4061.15 Dec-4-97
407	Fixed an n32 ABI bug. New libtool, auto* support.
408
4091.14 May-13-97
410	libtool is now used to generate shared and static libraries.
411	Fixed a minor portability problem reported by Russ McManus
412	<mcmanr@eq.gs.com>.
413
4141.13 Dec-2-96
415	Added --enable-purify-safety to keep Purify from complaining
416	about certain low level code.
417	Sparc fix for calling functions with < 6 args.
418	Linux x86 a.out fix.
419
4201.12 Nov-22-96
421	Added missing ffi_type_void, needed for supporting void return 
422	types. Fixed test case for non MIPS machines. Cygnus Support 
423	is now Cygnus Solutions. 
424
4251.11 Oct-30-96
426	Added notes about GNU make.
427
4281.10 Oct-29-96
429	Added configuration fix for non GNU compilers.
430
4311.09 Oct-29-96
432	Added --enable-debug configure switch. Clean-ups based on LCLint 
433	feedback. ffi_mips.h is always installed. Many configuration 
434	fixes. Fixed ffitest.c for sparc builds.
435
4361.08 Oct-15-96
437	Fixed n32 problem. Many clean-ups.
438
4391.07 Oct-14-96
440	Gordon Irlam rewrites v8.S again. Bug fixes.
441
4421.06 Oct-14-96
443	Gordon Irlam improved the sparc port. 
444
4451.05 Oct-14-96
446	Interface changes based on feedback.
447
4481.04 Oct-11-96
449	Sparc port complete (modulo struct passing bug).
450
4511.03 Oct-10-96
452	Passing struct args, and returning struct values works for
453	all architectures/calling conventions. Expanded tests.
454
4551.02 Oct-9-96
456	Added SGI n32 support. Fixed bugs in both o32 and Linux support.
457	Added "make test".
458
4591.01 Oct-8-96
460	Fixed float passing bug in mips version. Restructured some
461	of the code. Builds cleanly with SGI tools.
462
4631.00 Oct-7-96
464	First release. No public announcement.
465
466
467Authors & Credits
468=================
469
470libffi was written by Anthony Green <green@cygnus.com>.
471
472Portions of libffi were derived from Gianni Mariani's free gencall
473library for Silicon Graphics machines.
474
475The closure mechanism was designed and implemented by Kresten Krab
476Thorup.
477
478The Sparc port was derived from code contributed by the fine folks at
479Visible Decisions Inc <http://www.vdi.com>. Further enhancements were
480made by Gordon Irlam at Cygnus Solutions <http://www.cygnus.com>.
481
482The Alpha port was written by Richard Henderson at Cygnus Solutions.
483
484Andreas Schwab ported libffi to m68k Linux and provided a number of
485bug fixes.
486
487Geoffrey Keating ported libffi to the PowerPC.
488
489Raffaele Sena ported libffi to the ARM.
490
491Jesper Skov and Andrew Haley both did more than their fair share of
492stepping through the code and tracking down bugs.
493
494Thanks also to Tom Tromey for bug fixes and configuration help.
495
496Thanks to Jim Blandy, who provided some useful feedback on the libffi
497interface.
498
499If you have a problem, or have found a bug, please send a note to
500green@cygnus.com.