libffi/README

   1 README for libffi-2.00
   2
   3 libffi-2.00 has not been released yet! This is a development snapshot!
   4
   5 libffi-1.20 was released on [SOME FUTURE DAY]. Check the libffi web
   6 page for updates: <URL:http://sourceware.cygnus.com/libffi/>.
   7
   8
   9 What is libffi?
  10 ===============
  11
  12 Compilers for high level languages generate code that follow certain
  13 conventions. These conventions are necessary, in part, for separate
  14 compilation to work. One such convention is the "calling
  15 convention". The "calling convention" is essentially a set of
  16 assumptions made by the compiler about where function arguments will
  17 be found on entry to a function. A "calling convention" also specifies
  18 where the return value for a function is found.
  19
  20 Some programs may not know at the time of compilation what arguments
  21 are to be passed to a function. For instance, an interpreter may be
  22 told at run-time about the number and types of arguments used to call
  23 a given function. Libffi can be used in such programs to provide a
  24 bridge from the interpreter program to compiled code.
  25
  26 The libffi library provides a portable, high level programming
  27 interface to various calling conventions. This allows a programmer to
  28 call any function specified by a call interface description at run
  29 time.
  30
  31 Ffi stands for Foreign Function Interface. A foreign function
  32 interface is the popular name for the interface that allows code
  33 written in one language to call code written in another language. The
  34 libffi library really only provides the lowest, machine dependent
  35 layer of a fully featured foreign function interface. A layer must
  36 exist above libffi that handles type conversions for values passed
  37 between the two languages.
  38
  39
  40 Supported Platforms and Prerequisites
  41 =====================================
  42
  43 Libffi has been ported to:
  44
  45         SunOS 4.1.3 & Solaris 2.x (Sparc v8)
  46
  47         Irix 5.3 & 6.2 (System V/o32 & n32)
  48
  49         Intel x86 - Linux (System V ABI)
  50
  51         Alpha - Linux and OSF/1
  52
  53         m68k - Linux (System V ABI)
  54
  55         PowerPC - Linux (System V ABI)
  56
  57         ARM - Linux (System V ABI)
  58
  59 Libffi has been tested with the egcs 1.0.2 gcc compiler. Chances are
  60 that other versions will work.  Libffi has also been built and tested
  61 with the SGI compiler tools.
  62
  63 On PowerPC, the tests failed (see the note below).
  64
  65 You must use GNU make to build libffi. SGI's make will not work.
  66 Sun's probably won't either.
  67
  68 If you port libffi to another platform, please let me know! I assume
  69 that some will be easy (x86 NetBSD), and others will be more difficult
  70 (HP, AIX).
  71
  72
  73 Installing libffi
  74 =================
  75
  76 [Note: before actually performing any of these installation steps,
  77  you may wish to read the "Platform Specific Notes" below.]
  78
  79 First you must configure the distribution for your particular
  80 system. Go to the directory you wish to build libffi in and run the
  81 "configure" program found in the root directory of the libffi source
  82 distribution.
  83
  84 You may want to tell configure where to install the libffi library and
  85 header files. To do that, use the --prefix configure switch.  Libffi
  86 will install under /usr/local by default.
  87
  88 If you want to enable extra run-time debugging checks use the the
  89 --enable-debug configure switch. This is useful when your program dies
  90 mysteriously while using libffi.
  91
  92 Another useful configure switch is --enable-purify-safety. Using this
  93 will add some extra code which will suppress certain warnings when you
  94 are using Purify with libffi. Only use this switch when using
  95 Purify, as it will slow down the library.
  96
  97 Configure has many other options. Use "configure --help" to see them all.
  98
  99 Once configure has finished, type "make". Note that you must be using
 100 GNU make. SGI's make will not work.  Sun's probably won't either.
 101 You can ftp GNU make from prep.ai.mit.edu:/pub/gnu.
 102
 103 To ensure that libffi is working as advertised, type "make test".
 104
 105 To install the library and header files, type "make install".
 106
 107
 108 Using libffi
 109 ============
 110
 111         The Basics
 112         ----------
 113
 114 Libffi assumes that you have a pointer to the function you wish to
 115 call and that you know the number and types of arguments to pass it,
 116 as well as the return type of the function.
 117
 118 The first thing you must do is create an ffi_cif object that matches
 119 the signature of the function you wish to call. The cif in ffi_cif
 120 stands for Call InterFace. To prepare a call interface object, use the
 121 following function:
 122
 123 ffi_status ffi_prep_cif(ffi_cif *cif, ffi_abi abi,
 124                         unsigned int nargs,
 125                         ffi_type *rtype, ffi_type **atypes);
 126
 127         CIF is a pointer to the call interface object you wish
 128                 to initialize.
 129
 130         ABI is an enum that specifies the calling convention
 131                 to use for the call. FFI_DEFAULT_ABI defaults
 132                 to the system's native calling convention. Other
 133                 ABI's may be used with care. They are system
 134                 specific.
 135
 136         NARGS is the number of arguments this function accepts.
 137                 libffi does not yet support vararg functions.
 138
 139         RTYPE is a pointer to an ffi_type structure that represents
 140                 the return type of the function. Ffi_type objects
 141                 describe the types of values. libffi provides
 142                 ffi_type objects for many of the native C types:
 143                 signed int, unsigned int, signed char, unsigned char,
 144                 etc. There is also a pointer ffi_type object and
 145                 a void ffi_type. Use &ffi_type_void for functions that
 146                 don't return values.
 147
 148         ATYPES is a vector of ffi_type pointers. ARGS must be NARGS long.
 149                 If NARGS is 0, this is ignored.
 150
 151
 152 ffi_prep_cif will return a status code that you are responsible
 153 for checking. It will be one of the following:
 154
 155         FFI_OK - All is good.
 156
 157         FFI_BAD_TYPEDEF - One of the ffi_type objects that ffi_prep_cif
 158                 came across is bad.
 159
 160
 161 Before making the call, the VALUES vector should be initialized
 162 with pointers to the appropriate argument values.
 163
 164 To call the the function using the initialized ffi_cif, use the
 165 ffi_call function:
 166
 167 void ffi_call(ffi_cif *cif, void *fn, void *rvalue, void **avalues);
 168
 169         CIF is a pointer to the ffi_cif initialized specifically
 170                 for this function.
 171
 172         FN is a pointer to the function you want to call.
 173
 174         RVALUE is a pointer to a chunk of memory that is to hold the
 175                 result of the function call. Currently, it must be
 176                 at least one word in size (except for the n32 version
 177                 under Irix 6.x, which must be a pointer to an 8 byte
 178                 aligned value (a long long). It must also be at least
 179                 word aligned (depending on the return type, and the
 180                 system's alignment requirements). If RTYPE is
 181                 &ffi_type_void, this is ignored. If RVALUE is NULL,
 182                 the return value is discarded.
 183
 184         AVALUES is a vector of void* that point to the memory locations
 185                 holding the argument values for a call.
 186                 If NARGS is 0, this is ignored.
 187
 188
 189 If you are expecting a return value from FN it will have been stored
 190 at RVALUE.
 191
 192
 193
 194         An Example
 195         ----------
 196
 197 Here is a trivial example that calls puts() a few times.
 198
 199     #include <stdio.h>
 200     #include <ffi.h>
 201
 202     int main()
 203     {
 204       ffi_cif cif;
 205       ffi_type *args[1];
 206       void *values[1];
 207       char *s;
 208       int rc;
 209
 210       /* Initialize the argument info vectors */
 211       args[0] = &ffi_type_uint;
 212       values[0] = &s;
 213
 214       /* Initialize the cif */
 215       if (ffi_prep_cif(&cif, FFI_DEFAULT_ABI, 1,
 216                        &ffi_type_uint, args) == FFI_OK)
 217         {
 218           s = "Hello World!";
 219           ffi_call(&cif, puts, &rc, values);
 220           /* rc now holds the result of the call to puts */
 221
 222           /* values holds a pointer to the function's arg, so to
 223              call puts() again all we need to do is change the
 224              value of s */
 225           s = "This is cool!";
 226           ffi_call(&cif, puts, &rc, values);
 227         }
 228
 229       return 0;
 230     }
 231
 232
 233
 234         Aggregate Types
 235         ---------------
 236
 237 Although libffi has no special support for unions or bit-fields, it is
 238 perfectly happy passing structures back and forth. You must first
 239 describe the structure to libffi by creating a new ffi_type object
 240 for it. Here is the definition of ffi_type:
 241
 242     typedef struct _ffi_type
 243     {
 244       unsigned size;
 245       short alignment;
 246       short type;
 247       struct _ffi_type **elements;
 248     } ffi_type;
 249
 250 All structures must have type set to FFI_TYPE_STRUCT.  You may set
 251 size and alignment to 0. These will be calculated and reset to the
 252 appropriate values by ffi_prep_cif().
 253
 254 elements is a NULL terminated array of pointers to ffi_type objects
 255 that describe the type of the structure elements. These may, in turn,
 256 be structure elements.
 257
 258 The following example initializes a ffi_type object representing the
 259 tm struct from Linux's time.h:
 260
 261                                     struct tm {
 262                                         int tm_sec;
 263                                         int tm_min;
 264                                         int tm_hour;
 265                                         int tm_mday;
 266                                         int tm_mon;
 267                                         int tm_year;
 268                                         int tm_wday;
 269                                         int tm_yday;
 270                                         int tm_isdst;
 271                                         /* Those are for future use. */
 272                                         long int __tm_gmtoff__;
 273                                         __const char *__tm_zone__;
 274                                     };
 275
 276     {
 277       ffi_type tm_type;
 278       ffi_type *tm_type_elements[12];
 279       int i;
 280
 281       tm_type.size = tm_type.alignment = 0;
 282       tm_type.elements = &tm_type_elements;
 283
 284       for (i = 0; i < 9; i++)
 285           tm_type_elements[i] = &ffi_type_sint;
 286
 287       tm_type_elements[9] = &ffi_type_slong;
 288       tm_type_elements[10] = &ffi_type_pointer;
 289       tm_type_elements[11] = NULL;
 290
 291       /* tm_type can now be used to represent tm argument types and
 292          return types for ffi_prep_cif() */
 293     }
 294
 295
 296
 297 Platform Specific Notes
 298 =======================
 299
 300         Intel x86
 301         ---------
 302
 303 There are no known problems with the x86 port.
 304
 305         Sun Sparc - SunOS 4.1.3 & Solaris 2.x
 306         -------------------------------------
 307
 308 There's a bug in the structure passing code for sparc processors.
 309 Struct arguments that are passed in value actually end up being passed
 310 by reference. This will be fixed Real Soon Now.
 311
 312 "long long" values are not supported yet.
 313
 314 You must use GNU Make to build libffi on Sun platforms.
 315
 316         MIPS - Irix 5.3 & 6.x
 317         ---------------------
 318
 319 Irix 6.2 and better supports three different calling conventions: o32,
 320 n32 and n64. Currently, libffi only supports both o32 and n32 under
 321 Irix 6.x, but only o32 under Irix 5.3. Libffi will automatically be
 322 configured for whichever calling convention it was built for.
 323
 324 By default, the configure script will try to build libffi with the GNU
 325 development tools. To build libffi with the SGI development tools, set
 326 the environment variable CC to either "cc -32" or "cc -n32" before
 327 running configure under Irix 6.x (depending on whether you want an o32
 328 or n32 library), or just "cc" for Irix 5.3.
 329
 330 With the n32 calling convention, when returning structures smaller
 331 than 16 bytes, be sure to provide an RVALUE that is 8 byte aligned.
 332 Here's one way of forcing this:
 333
 334         double struct_storage[2];
 335         my_small_struct *s = (my_small_struct *) struct_storage;
 336         /* Use s for RVALUE */
 337
 338 If you don't do this you are liable to get spurious bus errors.
 339
 340 "long long" values are not supported yet.
 341
 342 You must use GNU Make to build libffi on SGI platforms.
 343
 344         ARM - System V ABI
 345         ------------------
 346
 347 The ARM port was performed on a NetWinder running ARM Linux ELF
 348 (2.0.31) and gcc 2.8.1.
 349
 350
 351
 352         PowerPC System V ABI
 353         --------------------
 354
 355 There are two `System V ABI's which libffi implements for PowerPC.
 356 They differ only in how small structures are returned from functions.
 357
 358 In the FFI_SYSV version, structures that are 8 bytes or smaller are
 359 returned in registers.  This is what GCC does when it is configured
 360 for solaris, and is what the System V ABI I have (dated September
 361 1995) says.
 362
 363 In the FFI_GCC_SYSV version, all structures are returned the same way:
 364 by passing a pointer as the first argument to the function.  This is
 365 what GCC does when it is configured for linux or a generic sysv
 366 target.
 367
 368 EGCS 1.0.1 (and probably other versions of EGCS/GCC) also has a
 369 inconsistency with the SysV ABI: When a procedure is called with many
 370 floating-point arguments, some of them get put on the stack.  They are
 371 all supposed to be stored in double-precision format, even if they are
 372 only single-precision, but EGCS stores single-precision arguments as
 373 single-precision anyway.  This causes one test to fail (the `many
 374 arguments' test).
 375
 376
 377 What's With The Crazy Comments?
 378 ===============================
 379
 380 You might notice a number of cryptic comments in the code, delimited
 381 by /*@ and @*/. These are annotations read by the program LCLint, a
 382 tool for statically checking C programs. You can read all about it at
 383 <http://larch-www.lcs.mit.edu:8001/larch/lclint/index.html>.
 384
 385
 386 History
 387 =======
 388
 389 1.20 Oct-5-98
 390         Raffaele Sena produces ARM port.
 391
 392 1.19 Oct-5-98
 393         Fixed x86 long double and long long return support.
 394         m68k bug fixes from Andreas Schwab.
 395         Patch for DU assembler compatibility for the Alpha from Richard
 396         Henderson.
 397
 398 1.18 Apr-17-98
 399         Bug fixes and MIPS configuration changes.
 400
 401 1.17 Feb-24-98
 402         Bug fixes and m68k port from Andreas Schwab. PowerPC port from
 403         Geoffrey Keating. Various bug x86, Sparc and MIPS bug fixes.
 404
 405 1.16 Feb-11-98
 406         Richard Henderson produces Alpha port.
 407
 408 1.15 Dec-4-97
 409         Fixed an n32 ABI bug. New libtool, auto* support.
 410
 411 1.14 May-13-97
 412         libtool is now used to generate shared and static libraries.
 413         Fixed a minor portability problem reported by Russ McManus
 414         <mcmanr@eq.gs.com>.
 415
 416 1.13 Dec-2-96
 417         Added --enable-purify-safety to keep Purify from complaining
 418         about certain low level code.
 419         Sparc fix for calling functions with < 6 args.
 420         Linux x86 a.out fix.
 421
 422 1.12 Nov-22-96
 423         Added missing ffi_type_void, needed for supporting void return
 424         types. Fixed test case for non MIPS machines. Cygnus Support
 425         is now Cygnus Solutions.
 426
 427 1.11 Oct-30-96
 428         Added notes about GNU make.
 429
 430 1.10 Oct-29-96
 431         Added configuration fix for non GNU compilers.
 432
 433 1.09 Oct-29-96
 434         Added --enable-debug configure switch. Clean-ups based on LCLint
 435         feedback. ffi_mips.h is always installed. Many configuration
 436         fixes. Fixed ffitest.c for sparc builds.
 437
 438 1.08 Oct-15-96
 439         Fixed n32 problem. Many clean-ups.
 440
 441 1.07 Oct-14-96
 442         Gordon Irlam rewrites v8.S again. Bug fixes.
 443
 444 1.06 Oct-14-96
 445         Gordon Irlam improved the sparc port.
 446
 447 1.05 Oct-14-96
 448         Interface changes based on feedback.
 449
 450 1.04 Oct-11-96
 451         Sparc port complete (modulo struct passing bug).
 452
 453 1.03 Oct-10-96
 454         Passing struct args, and returning struct values works for
 455         all architectures/calling conventions. Expanded tests.
 456
 457 1.02 Oct-9-96
 458         Added SGI n32 support. Fixed bugs in both o32 and Linux support.
 459         Added "make test".
 460
 461 1.01 Oct-8-96
 462         Fixed float passing bug in mips version. Restructured some
 463         of the code. Builds cleanly with SGI tools.
 464
 465 1.00 Oct-7-96
 466         First release. No public announcement.
 467
 468
 469 Authors & Credits
 470 =================
 471
 472 libffi was written by Anthony Green <green@cygnus.com>.
 473
 474 Portions of libffi were derived from Gianni Mariani's free gencall
 475 library for Silicon Graphics machines.
 476
 477 The closure mechanism was designed and implemented by Kresten Krab
 478 Thorup.
 479
 480 The Sparc port was derived from code contributed by the fine folks at
 481 Visible Decisions Inc <http://www.vdi.com>. Further enhancements were
 482 made by Gordon Irlam at Cygnus Solutions <http://www.cygnus.com>.
 483
 484 The Alpha port was written by Richard Henderson at Cygnus Solutions.
 485
 486 Andreas Schwab ported libffi to m68k Linux and provided a number of
 487 bug fixes.
 488
 489 Geoffrey Keating ported libffi to the PowerPC.
 490
 491 Raffaele Sena ported libffi to the ARM.
 492
 493 Jesper Skov and Andrew Haley both did more than their fair share of
 494 stepping through the code and tracking down bugs.
 495
 496 Thanks also to Tom Tromey for bug fixes and configuration help.
 497
 498 Thanks to Jim Blandy, who provided some useful feedback on the libffi
 499 interface.
 500
 501 If you have a problem, or have found a bug, please send a note to
 502 green@cygnus.com.