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1 .Dd February 15, 2008
2 .Dt ffi_call 3
3 .Sh NAME
4 .Nm ffi_call
5 .Nd Invoke a foreign function.
6 .Sh SYNOPSIS
7 .In ffi.h
8 .Ft void
9 .Fo ffi_call
10 .Fa "ffi_cif *cif"
11 .Fa "void (*fn)(void)"
12 .Fa "void *rvalue"
13 .Fa "void **avalue"
14 .Fc
15 .Sh DESCRIPTION
16 The
17 .Nm ffi_call
18 function provides a simple mechanism for invoking a function without
19 requiring knowledge of the function's interface at compile time.
20 .Fa fn
21 is called with the values retrieved from the pointers in the
22 .Fa avalue
23 array. The return value from
24 .Fa fn
25 is placed in storage pointed to by
26 .Fa rvalue .
27 .Fa cif
28 contains information describing the data types, sizes and alignments of the
29 arguments to and return value from
30 .Fa fn ,
31 and must be initialized with
32 .Nm ffi_prep_cif
33 before it is used with
34 .Nm ffi_call .
35 .Pp
36 .Fa rvalue
37 must point to storage that is sizeof(ffi_arg) or larger for non-floating point
38 types. For smaller-sized return value types, the
39 .Nm ffi_arg
40 or
41 .Nm ffi_sarg
42 integral type must be used to hold
43 the return value.
44 .Sh EXAMPLES
45 .Bd -literal
46 #include <ffi.h>
47 #include <stdio.h>
48
49 unsigned char
50 foo(unsigned int, float);
51
52 int
53 main(int argc, const char **argv)
54 {
55 ffi_cif cif;
56 ffi_type *arg_types[2];
57 void *arg_values[2];
58 ffi_status status;
59
60 // Because the return value from foo() is smaller than sizeof(long), it
61 // must be passed as ffi_arg or ffi_sarg.
62 ffi_arg result;
63
64 // Specify the data type of each argument. Available types are defined
65 // in <ffi/ffi.h>.
66 arg_types[0] = &ffi_type_uint;
67 arg_types[1] = &ffi_type_float;
68
69 // Prepare the ffi_cif structure.
70 if ((status = ffi_prep_cif(&cif, FFI_DEFAULT_ABI,
71 2, &ffi_type_uint8, arg_types)) != FFI_OK)
72 {
73 // Handle the ffi_status error.
74 }
75
76 // Specify the values of each argument.
77 unsigned int arg1 = 42;
78 float arg2 = 5.1;
79
80 arg_values[0] = &arg1;
81 arg_values[1] = &arg2;
82
83 // Invoke the function.
84 ffi_call(&cif, FFI_FN(foo), &result, arg_values);
85
86 // The ffi_arg 'result' now contains the unsigned char returned from foo(),
87 // which can be accessed by a typecast.
88 printf("result is %hhu", (unsigned char)result);
89
90 return 0;
91 }
92
93 // The target function.
94 unsigned char
95 foo(unsigned int x, float y)
96 {
97 unsigned char result = x - y;
98 return result;
99 }
100 .Ed
101 .Sh SEE ALSO
102 .Xr ffi 3 ,
103 .Xr ffi_prep_cif 3