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+.Dd February 15, 2008
+.Dt ffi_call 3
+.Sh NAME
+.Nm ffi_call
+.Nd Invoke a foreign function.
+.Sh SYNOPSIS
+.In ffi.h
+.Ft void
+.Fo ffi_call
+.Fa "ffi_cif *cif"
+.Fa "void (*fn)(void)"
+.Fa "void *rvalue"
+.Fa "void **avalue"
+.Fc
+.Sh DESCRIPTION
+The
+.Nm ffi_call
+function provides a simple mechanism for invoking a function without
+requiring knowledge of the function's interface at compile time.
+.Fa fn
+is called with the values retrieved from the pointers in the
+.Fa avalue
+array. The return value from
+.Fa fn
+is placed in storage pointed to by
+.Fa rvalue .
+.Fa cif
+contains information describing the data types, sizes and alignments of the
+arguments to and return value from
+.Fa fn ,
+and must be initialized with
+.Nm ffi_prep_cif
+before it is used with
+.Nm ffi_call .
+.Pp
+.Fa rvalue
+must point to storage that is sizeof(long) or larger. For smaller
+return value sizes, the
+.Nm ffi_arg
+or
+.Nm ffi_sarg
+integral type must be used to hold
+the return value.
+.Sh EXAMPLES
+.Bd -literal
+#include <ffi/ffi.h>
+#include <stdio.h>
+
+unsigned char
+foo(unsigned int, float);
+
+int
+main(int argc, const char **argv)
+{
+    ffi_cif cif;
+    ffi_type *arg_types[2];
+    void *arg_values[2];
+    ffi_status status;
+
+    // Because the return value from foo() is smaller than sizeof(long), it
+    // must be passed as ffi_arg or ffi_sarg.
+    ffi_arg result;
+
+    // Specify the data type of each argument. Available types are defined
+    // in <ffi/ffi.h>.
+    arg_types[0] = &ffi_type_uint;
+    arg_types[1] = &ffi_type_float;
+
+    // Prepare the ffi_cif structure.
+    if ((status = ffi_prep_cif(&cif, FFI_DEFAULT_ABI,
+        2, &ffi_type_uint8, arg_types)) != FFI_OK)
+    {
+        // Handle the ffi_status error.
+    }
+
+    // Specify the values of each argument.
+    unsigned int arg1 = 42;
+    float arg2 = 5.1;
+
+    arg_values[0] = &arg1;
+    arg_values[1] = &arg2;
+
+    // Invoke the function.
+    ffi_call(&cif, FFI_FN(foo), &result, arg_values);
+
+    // The ffi_arg 'result' now contains the unsigned char returned from foo(),
+    // which can be accessed by a typecast.
+    printf("result is %hhu", (unsigned char)result);
+
+    return 0;
+}
+
+// The target function.
+unsigned char
+foo(unsigned int x, float y)
+{
+    unsigned char result = x - y;
+    return result;
+}
+.Ed
+.Sh SEE ALSO
+.Xr ffi 3 ,
+.Xr ffi_prep_cif 3