libffi/README

   1 This directory contains the libffi package, which is not part of GCC but
   2 shipped with GCC as convenience.
   3
   4 Status
   5 ======
   6
   7 libffi-2.00 has not been released yet! This is a development snapshot!
   8
   9 libffi-1.20 was released on October 5, 1998. Check the libffi web
  10 page for updates: <URL:http://sources.redhat.com/libffi/>.
  11
  12
  13 What is libffi?
  14 ===============
  15
  16 Compilers for high level languages generate code that follow certain
  17 conventions. These conventions are necessary, in part, for separate
  18 compilation to work. One such convention is the "calling
  19 convention". The "calling convention" is essentially a set of
  20 assumptions made by the compiler about where function arguments will
  21 be found on entry to a function. A "calling convention" also specifies
  22 where the return value for a function is found.
  23
  24 Some programs may not know at the time of compilation what arguments
  25 are to be passed to a function. For instance, an interpreter may be
  26 told at run-time about the number and types of arguments used to call
  27 a given function. Libffi can be used in such programs to provide a
  28 bridge from the interpreter program to compiled code.
  29
  30 The libffi library provides a portable, high level programming
  31 interface to various calling conventions. This allows a programmer to
  32 call any function specified by a call interface description at run
  33 time.
  34
  35 Ffi stands for Foreign Function Interface. A foreign function
  36 interface is the popular name for the interface that allows code
  37 written in one language to call code written in another language. The
  38 libffi library really only provides the lowest, machine dependent
  39 layer of a fully featured foreign function interface. A layer must
  40 exist above libffi that handles type conversions for values passed
  41 between the two languages.
  42
  43
  44 Supported Platforms and Prerequisites
  45 =====================================
  46
  47 Libffi 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
  63 Libffi has been tested with the egcs 1.0.2 gcc compiler. Chances are
  64 that other versions will work.  Libffi has also been built and tested
  65 with the SGI compiler tools.
  66
  67 On PowerPC, the tests failed (see the note below).
  68
  69 You must use GNU make to build libffi. SGI's make will not work.
  70 Sun's probably won't either.
  71
  72 If you port libffi to another platform, please let me know! I assume
  73 that some will be easy (x86 NetBSD), and others will be more difficult
  74 (HP).
  75
  76
  77 Installing 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
  83 First you must configure the distribution for your particular
  84 system. 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
  86 distribution.
  87
  88 You may want to tell configure where to install the libffi library and
  89 header files. To do that, use the --prefix configure switch.  Libffi
  90 will install under /usr/local by default.
  91
  92 If you want to enable extra run-time debugging checks use the the
  93 --enable-debug configure switch. This is useful when your program dies
  94 mysteriously while using libffi.
  95
  96 Another useful configure switch is --enable-purify-safety. Using this
  97 will add some extra code which will suppress certain warnings when you
  98 are using Purify with libffi. Only use this switch when using
  99 Purify, as it will slow down the library.
 100
 101 Configure has many other options. Use "configure --help" to see them all.
 102
 103 Once configure has finished, type "make". Note that you must be using
 104 GNU make. SGI's make will not work.  Sun's probably won't either.
 105 You can ftp GNU make from prep.ai.mit.edu:/pub/gnu.
 106
 107 To ensure that libffi is working as advertised, type "make test".
 108
 109 To install the library and header files, type "make install".
 110
 111
 112 Using libffi
 113 ============
 114
 115         The Basics
 116         ----------
 117
 118 Libffi assumes that you have a pointer to the function you wish to
 119 call and that you know the number and types of arguments to pass it,
 120 as well as the return type of the function.
 121
 122 The first thing you must do is create an ffi_cif object that matches
 123 the signature of the function you wish to call. The cif in ffi_cif
 124 stands for Call InterFace. To prepare a call interface object, use the
 125 following function:
 126
 127 ffi_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
 156 ffi_prep_cif will return a status code that you are responsible
 157 for 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
 165 Before making the call, the VALUES vector should be initialized
 166 with pointers to the appropriate argument values.
 167
 168 To call the the function using the initialized ffi_cif, use the
 169 ffi_call function:
 170
 171 void 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
 193 If you are expecting a return value from FN it will have been stored
 194 at RVALUE.
 195
 196
 197
 198         An Example
 199         ----------
 200
 201 Here 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
 241 Although libffi has no special support for unions or bit-fields, it is
 242 perfectly happy passing structures back and forth. You must first
 243 describe the structure to libffi by creating a new ffi_type object
 244 for 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
 254 All structures must have type set to FFI_TYPE_STRUCT.  You may set
 255 size and alignment to 0. These will be calculated and reset to the
 256 appropriate values by ffi_prep_cif().
 257
 258 elements is a NULL terminated array of pointers to ffi_type objects
 259 that describe the type of the structure elements. These may, in turn,
 260 be structure elements.
 261
 262 The following example initializes a ffi_type object representing the
 263 tm 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
 301 Platform Specific Notes
 302 =======================
 303
 304         Intel x86
 305         ---------
 306
 307 There are no known problems with the x86 port.
 308
 309         Sun SPARC - SunOS 4.1.3 & Solaris 2.x
 310         -------------------------------------
 311
 312 You must use GNU Make to build libffi on Sun platforms.
 313
 314         MIPS - Irix 5.3 & 6.x
 315         ---------------------
 316
 317 Irix 6.2 and better supports three different calling conventions: o32,
 318 n32 and n64. Currently, libffi only supports both o32 and n32 under
 319 Irix 6.x, but only o32 under Irix 5.3. Libffi will automatically be
 320 configured for whichever calling convention it was built for.
 321
 322 By default, the configure script will try to build libffi with the GNU
 323 development tools. To build libffi with the SGI development tools, set
 324 the environment variable CC to either "cc -32" or "cc -n32" before
 325 running configure under Irix 6.x (depending on whether you want an o32
 326 or n32 library), or just "cc" for Irix 5.3.
 327
 328 With the n32 calling convention, when returning structures smaller
 329 than 16 bytes, be sure to provide an RVALUE that is 8 byte aligned.
 330 Here'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
 336 If you don't do this you are liable to get spurious bus errors.
 337
 338 "long long" values are not supported yet.
 339
 340 You must use GNU Make to build libffi on SGI platforms.
 341
 342         ARM - System V ABI
 343         ------------------
 344
 345 The 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
 353 There are two `System V ABI's which libffi implements for PowerPC.
 354 They differ only in how small structures are returned from functions.
 355
 356 In the FFI_SYSV version, structures that are 8 bytes or smaller are
 357 returned in registers.  This is what GCC does when it is configured
 358 for solaris, and is what the System V ABI I have (dated September
 359 1995) says.
 360
 361 In the FFI_GCC_SYSV version, all structures are returned the same way:
 362 by passing a pointer as the first argument to the function.  This is
 363 what GCC does when it is configured for linux or a generic sysv
 364 target.
 365
 366 EGCS 1.0.1 (and probably other versions of EGCS/GCC) also has a
 367 inconsistency with the SysV ABI: When a procedure is called with many
 368 floating-point arguments, some of them get put on the stack.  They are
 369 all supposed to be stored in double-precision format, even if they are
 370 only single-precision, but EGCS stores single-precision arguments as
 371 single-precision anyway.  This causes one test to fail (the `many
 372 arguments' test).
 373
 374
 375 History
 376 =======
 377
 378 1.20 Oct-5-98
 379         Raffaele Sena produces ARM port.
 380
 381 1.19 Oct-5-98
 382         Fixed x86 long double and long long return support.
 383         m68k bug fixes from Andreas Schwab.
 384         Patch for DU assembler compatibility for the Alpha from Richard
 385         Henderson.
 386
 387 1.18 Apr-17-98
 388         Bug fixes and MIPS configuration changes.
 389
 390 1.17 Feb-24-98
 391         Bug fixes and m68k port from Andreas Schwab. PowerPC port from
 392         Geoffrey Keating. Various bug x86, Sparc and MIPS bug fixes.
 393
 394 1.16 Feb-11-98
 395         Richard Henderson produces Alpha port.
 396
 397 1.15 Dec-4-97
 398         Fixed an n32 ABI bug. New libtool, auto* support.
 399
 400 1.14 May-13-97
 401         libtool is now used to generate shared and static libraries.
 402         Fixed a minor portability problem reported by Russ McManus
 403         <mcmanr@eq.gs.com>.
 404
 405 1.13 Dec-2-96
 406         Added --enable-purify-safety to keep Purify from complaining
 407         about certain low level code.
 408         Sparc fix for calling functions with < 6 args.
 409         Linux x86 a.out fix.
 410
 411 1.12 Nov-22-96
 412         Added missing ffi_type_void, needed for supporting void return
 413         types. Fixed test case for non MIPS machines. Cygnus Support
 414         is now Cygnus Solutions.
 415
 416 1.11 Oct-30-96
 417         Added notes about GNU make.
 418
 419 1.10 Oct-29-96
 420         Added configuration fix for non GNU compilers.
 421
 422 1.09 Oct-29-96
 423         Added --enable-debug configure switch. Clean-ups based on LCLint
 424         feedback. ffi_mips.h is always installed. Many configuration
 425         fixes. Fixed ffitest.c for sparc builds.
 426
 427 1.08 Oct-15-96
 428         Fixed n32 problem. Many clean-ups.
 429
 430 1.07 Oct-14-96
 431         Gordon Irlam rewrites v8.S again. Bug fixes.
 432
 433 1.06 Oct-14-96
 434         Gordon Irlam improved the sparc port.
 435
 436 1.05 Oct-14-96
 437         Interface changes based on feedback.
 438
 439 1.04 Oct-11-96
 440         Sparc port complete (modulo struct passing bug).
 441
 442 1.03 Oct-10-96
 443         Passing struct args, and returning struct values works for
 444         all architectures/calling conventions. Expanded tests.
 445
 446 1.02 Oct-9-96
 447         Added SGI n32 support. Fixed bugs in both o32 and Linux support.
 448         Added "make test".
 449
 450 1.01 Oct-8-96
 451         Fixed float passing bug in mips version. Restructured some
 452         of the code. Builds cleanly with SGI tools.
 453
 454 1.00 Oct-7-96
 455         First release. No public announcement.
 456
 457
 458 Authors & Credits
 459 =================
 460
 461 libffi was written by Anthony Green <green@cygnus.com>.
 462
 463 Portions of libffi were derived from Gianni Mariani's free gencall
 464 library for Silicon Graphics machines.
 465
 466 The closure mechanism was designed and implemented by Kresten Krab
 467 Thorup.
 468
 469 The Sparc port was derived from code contributed by the fine folks at
 470 Visible Decisions Inc <http://www.vdi.com>. Further enhancements were
 471 made by Gordon Irlam at Cygnus Solutions <http://www.cygnus.com>.
 472
 473 The Alpha port was written by Richard Henderson at Cygnus Solutions.
 474
 475 Andreas Schwab ported libffi to m68k Linux and provided a number of
 476 bug fixes.
 477
 478 Geoffrey Keating ported libffi to the PowerPC.
 479
 480 Raffaele Sena ported libffi to the ARM.
 481
 482 Jesper Skov and Andrew Haley both did more than their fair share of
 483 stepping through the code and tracking down bugs.
 484
 485 Thanks also to Tom Tromey for bug fixes and configuration help.
 486
 487 Thanks to Jim Blandy, who provided some useful feedback on the libffi
 488 interface.
 489
 490 If you have a problem, or have found a bug, please send a note to
 491 green@cygnus.com.