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diff --git a/doc/.svn/text-base/libffi.info.svn-base b/doc/.svn/text-base/libffi.info.svn-base new file mode 100644 index 0000000..87dee8a --- /dev/null +++ b/doc/.svn/text-base/libffi.info.svn-base @@ -0,0 +1,533 @@ +This is doc/libffi.info, produced by makeinfo version 4.12 from +./doc/libffi.texi. + +This manual is for Libffi, a portable foreign-function interface +library. + + Copyright (C) 2008 Red Hat, Inc. + + Permission is granted to copy, distribute and/or modify this + document under the terms of the GNU General Public License as + published by the Free Software Foundation; either version 2, or + (at your option) any later version. A copy of the license is + included in the section entitled "GNU General Public License". + + +INFO-DIR-SECTION +START-INFO-DIR-ENTRY +* libffi: (libffi). Portable foreign-function interface library. +END-INFO-DIR-ENTRY + + +File: libffi.info, Node: Top, Next: Introduction, Up: (dir) + +libffi +****** + +This manual is for Libffi, a portable foreign-function interface +library. + + Copyright (C) 2008 Red Hat, Inc. + + Permission is granted to copy, distribute and/or modify this + document under the terms of the GNU General Public License as + published by the Free Software Foundation; either version 2, or + (at your option) any later version. A copy of the license is + included in the section entitled "GNU General Public License". + + +* Menu: + +* Introduction:: What is libffi? +* Using libffi:: How to use libffi. +* Missing Features:: Things libffi can't do. +* Index:: Index. + + +File: libffi.info, Node: Introduction, Next: Using libffi, Prev: Top, Up: Top + +1 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 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. The calling convention is also sometimes called the "ABI" or +"Application Binary Interface". + + 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. + + +File: libffi.info, Node: Using libffi, Next: Missing Features, Prev: Introduction, Up: Top + +2 Using libffi +************** + +* Menu: + +* The Basics:: The basic libffi API. +* Simple Example:: A simple example. +* Types:: libffi type descriptions. +* Multiple ABIs:: Different passing styles on one platform. +* The Closure API:: Writing a generic function. + + +File: libffi.info, Node: The Basics, Next: Simple Example, Up: Using libffi + +2.1 The Basics +============== + +`Libffi' assumes that you have a pointer to the function you wish to +call and that you know the number and types of arguments to pass it, as +well as the return type of the function. + + The first thing you must do is create an `ffi_cif' object that +matches the signature of the function you wish to call. This is a +separate step because it is common to make multiple calls using a +single `ffi_cif'. The "cif" in `ffi_cif' stands for Call InterFace. +To prepare a call interface object, use the function `ffi_prep_cif'. + + -- Function: ffi_status ffi_prep_cif (ffi_cif *CIF, ffi_abi ABI, + unsigned int NARGS, ffi_type *RTYPE, ffi_type **ARGTYPES) + This initializes CIF according to the given parameters. + + ABI is the ABI to use; normally `FFI_DEFAULT_ABI' is what you + want. *note Multiple ABIs:: for more information. + + NARGS is the number of arguments that this function accepts. + `libffi' does not yet handle varargs functions; see *note Missing + Features:: for more information. + + RTYPE is a pointer to an `ffi_type' structure that describes the + return type of the function. *Note Types::. + + ARGTYPES is a vector of `ffi_type' pointers. ARGTYPES must have + NARGS elements. If NARGS is 0, this argument is ignored. + + `ffi_prep_cif' returns a `libffi' status code, of type + `ffi_status'. This will be either `FFI_OK' if everything worked + properly; `FFI_BAD_TYPEDEF' if one of the `ffi_type' objects is + incorrect; or `FFI_BAD_ABI' if the ABI parameter is invalid. + + To call a function using an initialized `ffi_cif', use the +`ffi_call' function: + + -- Function: void ffi_call (ffi_cif *CIF, void *FN, void *RVALUE, void + **AVALUES) + This calls the function FN according to the description given in + CIF. CIF must have already been prepared using `ffi_prep_cif'. + + RVALUE is a pointer to a chunk of memory that will hold the result + of the function call. This must be large enough to hold the + result and must be suitably aligned; it is the caller's + responsibility to ensure this. If CIF declares that the function + returns `void' (using `ffi_type_void'), then RVALUE is ignored. + If RVALUE is `NULL', then the return value is discarded. + + AVALUES is a vector of `void *' pointers that point to the memory + locations holding the argument values for a call. If CIF declares + that the function has no arguments (i.e., NARGS was 0), then + AVALUES is ignored. + + +File: libffi.info, Node: Simple Example, Next: Types, Prev: The Basics, Up: Using libffi + +2.2 Simple Example +================== + +Here is a trivial example that calls `puts' a few times. + + #include <stdio.h> + #include <ffi.h> + + int main() + { + ffi_cif cif; + ffi_type *args[1]; + void *values[1]; + char *s; + int rc; + + /* Initialize the argument info vectors */ + args[0] = &ffi_type_pointer; + values[0] = &s; + + /* Initialize the cif */ + if (ffi_prep_cif(&cif, FFI_DEFAULT_ABI, 1, + &ffi_type_uint, args) == FFI_OK) + { + s = "Hello World!"; + ffi_call(&cif, puts, &rc, values); + /* rc now holds the result of the call to puts */ + + /* values holds a pointer to the function's arg, so to + call puts() again all we need to do is change the + value of s */ + s = "This is cool!"; + ffi_call(&cif, puts, &rc, values); + } + + return 0; + } + + +File: libffi.info, Node: Types, Next: Multiple ABIs, Prev: Simple Example, Up: Using libffi + +2.3 Types +========= + +* Menu: + +* Primitive Types:: Built-in types. +* Structures:: Structure types. +* Type Example:: Structure type example. + + +File: libffi.info, Node: Primitive Types, Next: Structures, Up: Types + +2.3.1 Primitive Types +--------------------- + +`Libffi' provides a number of built-in type descriptors that can be +used to describe argument and return types: + +`ffi_type_void' + The type `void'. This cannot be used for argument types, only for + return values. + +`ffi_type_uint8' + An unsigned, 8-bit integer type. + +`ffi_type_sint8' + A signed, 8-bit integer type. + +`ffi_type_uint16' + An unsigned, 16-bit integer type. + +`ffi_type_sint16' + A signed, 16-bit integer type. + +`ffi_type_uint32' + An unsigned, 32-bit integer type. + +`ffi_type_sint32' + A signed, 32-bit integer type. + +`ffi_type_uint64' + An unsigned, 64-bit integer type. + +`ffi_type_sint64' + A signed, 64-bit integer type. + +`ffi_type_float' + The C `float' type. + +`ffi_type_double' + The C `double' type. + +`ffi_type_uchar' + The C `unsigned char' type. + +`ffi_type_schar' + The C `signed char' type. (Note that there is not an exact + equivalent to the C `char' type in `libffi'; ordinarily you should + either use `ffi_type_schar' or `ffi_type_uchar' depending on + whether `char' is signed.) + +`ffi_type_ushort' + The C `unsigned short' type. + +`ffi_type_sshort' + The C `short' type. + +`ffi_type_uint' + The C `unsigned int' type. + +`ffi_type_sint' + The C `int' type. + +`ffi_type_ulong' + The C `unsigned long' type. + +`ffi_type_slong' + The C `long' type. + +`ffi_type_longdouble' + On platforms that have a C `long double' type, this is defined. + On other platforms, it is not. + +`ffi_type_pointer' + A generic `void *' pointer. You should use this for all pointers, + regardless of their real type. + + Each of these is of type `ffi_type', so you must take the address +when passing to `ffi_prep_cif'. + + +File: libffi.info, Node: Structures, Next: Type Example, Prev: Primitive Types, Up: Types + +2.3.2 Structures +---------------- + +Although `libffi' has no special support for unions or bit-fields, it +is perfectly happy passing structures back and forth. You must first +describe the structure to `libffi' by creating a new `ffi_type' object +for it. + + -- ffi_type: + The `ffi_type' has the following members: + `size_t size' + This is set by `libffi'; you should initialize it to zero. + + `unsigned short alignment' + This is set by `libffi'; you should initialize it to zero. + + `unsigned short type' + For a structure, this should be set to `FFI_TYPE_STRUCT'. + + `ffi_type **elements' + This is a `NULL'-terminated array of pointers to `ffi_type' + objects. There is one element per field of the struct. + + +File: libffi.info, Node: Type Example, Prev: Structures, Up: Types + +2.3.3 Type Example +------------------ + +The following example initializes a `ffi_type' object representing the +`tm' struct from Linux's `time.h'. + + Here is how the struct is defined: + + struct tm { + int tm_sec; + int tm_min; + int tm_hour; + int tm_mday; + int tm_mon; + int tm_year; + int tm_wday; + int tm_yday; + int tm_isdst; + /* Those are for future use. */ + long int __tm_gmtoff__; + __const char *__tm_zone__; + }; + + Here is the corresponding code to describe this struct to `libffi': + + { + ffi_type tm_type; + ffi_type *tm_type_elements[12]; + int i; + + tm_type.size = tm_type.alignment = 0; + tm_type.elements = &tm_type_elements; + + for (i = 0; i < 9; i++) + tm_type_elements[i] = &ffi_type_sint; + + tm_type_elements[9] = &ffi_type_slong; + tm_type_elements[10] = &ffi_type_pointer; + tm_type_elements[11] = NULL; + + /* tm_type can now be used to represent tm argument types and + return types for ffi_prep_cif() */ + } + + +File: libffi.info, Node: Multiple ABIs, Next: The Closure API, Prev: Types, Up: Using libffi + +2.4 Multiple ABIs +================= + +A given platform may provide multiple different ABIs at once. For +instance, the x86 platform has both `stdcall' and `fastcall' functions. + + `libffi' provides some support for this. However, this is +necessarily platform-specific. + + +File: libffi.info, Node: The Closure API, Prev: Multiple ABIs, Up: Using libffi + +2.5 The Closure API +=================== + +`libffi' also provides a way to write a generic function - a function +that can accept and decode any combination of arguments. This can be +useful when writing an interpreter, or to provide wrappers for +arbitrary functions. + + This facility is called the "closure API". Closures are not +supported on all platforms; you can check the `FFI_CLOSURES' define to +determine whether they are supported on the current platform. + + Because closures work by assembling a tiny function at runtime, they +require special allocation on platforms that have a non-executable +heap. Memory management for closures is handled by a pair of functions: + + -- Function: void *ffi_closure_alloc (size_t SIZE, void **CODE) + Allocate a chunk of memory holding SIZE bytes. This returns a + pointer to the writable address, and sets *CODE to the + corresponding executable address. + + SIZE should be sufficient to hold a `ffi_closure' object. + + -- Function: void ffi_closure_free (void *WRITABLE) + Free memory allocated using `ffi_closure_alloc'. The argument is + the writable address that was returned. + + Once you have allocated the memory for a closure, you must construct +a `ffi_cif' describing the function call. Finally you can prepare the +closure function: + + -- Function: ffi_status ffi_prep_closure_loc (ffi_closure *CLOSURE, + ffi_cif *CIF, void (*FUN) (ffi_cif *CIF, void *RET, void + **ARGS, void *USER_DATA), void *USER_DATA, void *CODELOC) + Prepare a closure function. + + CLOSURE is the address of a `ffi_closure' object; this is the + writable address returned by `ffi_closure_alloc'. + + CIF is the `ffi_cif' describing the function parameters. + + USER_DATA is an arbitrary datum that is passed, uninterpreted, to + your closure function. + + CODELOC is the executable address returned by `ffi_closure_alloc'. + + FUN is the function which will be called when the closure is + invoked. It is called with the arguments: + CIF + The `ffi_cif' passed to `ffi_prep_closure_loc'. + + RET + A pointer to the memory used for the function's return value. + FUN must fill this, unless the function is declared as + returning `void'. + + ARGS + A vector of pointers to memory holding the arguments to the + function. + + USER_DATA + The same USER_DATA that was passed to `ffi_prep_closure_loc'. + + `ffi_prep_closure_loc' will return `FFI_OK' if everything went ok, + and something else on error. + + After calling `ffi_prep_closure_loc', you can cast CODELOC to the + appropriate pointer-to-function type. + + You may see old code referring to `ffi_prep_closure'. This function +is deprecated, as it cannot handle the need for separate writable and +executable addresses. + + +File: libffi.info, Node: Missing Features, Next: Index, Prev: Using libffi, Up: Top + +3 Missing Features +****************** + +`libffi' is missing a few features. We welcome patches to add support +for these. + + * There is no support for calling varargs functions. This may work + on some platforms, depending on how the ABI is defined, but it is + not reliable. + + * There is no support for bit fields in structures. + + * The closure API is + + * The "raw" API is undocumented. + + +File: libffi.info, Node: Index, Prev: Missing Features, Up: Top + +Index +***** + + +* Menu: + +* : Structures. (line 12) +* ABI: Introduction. (line 13) +* Application Binary Interface: Introduction. (line 13) +* calling convention: Introduction. (line 13) +* cif: The Basics. (line 14) +* closure API: The Closure API. (line 13) +* closures: The Closure API. (line 13) +* FFI: Introduction. (line 31) +* ffi_call: The Basics. (line 41) +* ffi_closure_alloca: The Closure API. (line 19) +* ffi_closure_free: The Closure API. (line 26) +* FFI_CLOSURES: The Closure API. (line 13) +* ffi_prep_cif: The Basics. (line 16) +* ffi_prep_closure_loc: The Closure API. (line 34) +* ffi_status <1>: The Closure API. (line 37) +* ffi_status: The Basics. (line 18) +* ffi_type: Structures. (line 11) +* ffi_type_double: Primitive Types. (line 41) +* ffi_type_float: Primitive Types. (line 38) +* ffi_type_longdouble: Primitive Types. (line 71) +* ffi_type_pointer: Primitive Types. (line 75) +* ffi_type_schar: Primitive Types. (line 47) +* ffi_type_sint: Primitive Types. (line 62) +* ffi_type_sint16: Primitive Types. (line 23) +* ffi_type_sint32: Primitive Types. (line 29) +* ffi_type_sint64: Primitive Types. (line 35) +* ffi_type_sint8: Primitive Types. (line 17) +* ffi_type_slong: Primitive Types. (line 68) +* ffi_type_sshort: Primitive Types. (line 56) +* ffi_type_uchar: Primitive Types. (line 44) +* ffi_type_uint: Primitive Types. (line 59) +* ffi_type_uint16: Primitive Types. (line 20) +* ffi_type_uint32: Primitive Types. (line 26) +* ffi_type_uint64: Primitive Types. (line 32) +* ffi_type_uint8: Primitive Types. (line 14) +* ffi_type_ulong: Primitive Types. (line 65) +* ffi_type_ushort: Primitive Types. (line 53) +* ffi_type_void: Primitive Types. (line 10) +* Foreign Function Interface: Introduction. (line 31) +* void <1>: The Closure API. (line 20) +* void: The Basics. (line 43) + + + +Tag Table: +Node: Top670 +Node: Introduction1406 +Node: Using libffi3042 +Node: The Basics3477 +Node: Simple Example6084 +Node: Types7111 +Node: Primitive Types7394 +Node: Structures9214 +Node: Type Example10074 +Node: Multiple ABIs11297 +Node: The Closure API11668 +Node: Missing Features14588 +Node: Index15081 + +End Tag Table |