ffi_call(3) [centos man page]
ffi_call(3) BSD Library Functions Manual ffi_call(3) NAME
ffi_call -- Invoke a foreign function. SYNOPSIS
#include <ffi.h> void ffi_call(ffi_cif *cif, void (*fn)(void), void *rvalue, void **avalue); DESCRIPTION
The ffi_call function provides a simple mechanism for invoking a function without requiring knowledge of the function's interface at compile time. fn is called with the values retrieved from the pointers in the avalue array. The return value from fn is placed in storage pointed to by rvalue. cif contains information describing the data types, sizes and alignments of the arguments to and return value from fn, and must be initialized with ffi_prep_cif before it is used with ffi_call. rvalue must point to storage that is sizeof(ffi_arg) or larger for non-floating point types. For smaller-sized return value types, the ffi_arg or ffi_sarg integral type must be used to hold the return value. EXAMPLES
#include <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; } SEE ALSO
ffi(3), ffi_prep_cif(3) February 15, 2008
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ffi_prep_closure(3) BSD Library Functions Manual ffi_prep_closure(3) NAME
ffi_prep_closure -- Prepare a ffi_closure for execution. SYNOPSIS
#include <ffi/ffi.h> ffi_status ffi_prep_closure(ffi_closure *closure, ffi_cif *cif, void (*fun)(ffi_cif*,void*,void**,void*), void *user_data); DESCRIPTION
closure is prepared to execute fun. cif contains information describing the data types, sizes and alignments of the arguments to and return value from the function that will be called from fun, and must be initialized with ffi_prep_cif before it is used with ffi_prep_closure. user_data may point to additional data to be used in fun. If no additional data is needed, user_data may be NULL. When closure is invoked, fun is called with cif, an array of pointers to arguments, a pointer to a return value, and user_data. Some architectures do not allow the execution of data by default. In such cases, it is necessary to manually alter the permissions of the page that contains closure prior to its execution. RETURN VALUES
Upon successful completion, ffi_prep_closure returns FFI_OK. If the ABI specified in cif does not refer to a valid ABI, FFI_BAD_ABI will be returned. Available ABIs are defined in <ffi/ppc-ffitarget.h> and <ffi/x86-ffitarget.h>. EXAMPLES
#define MACOSX // for fficonfig.h on Darwin #include <ffi/ffi.h> #include <sys/mman.h> // for mmap() unsigned char foo(unsigned int, float); static void foo_closure(ffi_cif*, void*, void**, void*); int main(int argc, const char **argv) { ffi_cif cif; ffi_closure *closure; ffi_type *arg_types[2]; ffi_arg result; ffi_status status; // 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; // Allocate a page to hold the closure with read and write permissions. if ((closure = mmap(NULL, sizeof(ffi_closure), PROT_READ | PROT_WRITE, MAP_ANON | MAP_PRIVATE, -1, 0)) == (void*)-1) { // Check errno and handle the error. } // 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. } // Prepare the ffi_closure structure. if ((status = ffi_prep_closure(closure, &cif, foo_closure, NULL)) != FFI_OK) { // Handle the ffi_status error. } // Ensure that the closure will execute on all architectures. if (mprotect(closure, sizeof(closure), PROT_READ | PROT_EXEC) == -1) { // Check errno and handle the error. } // The closure is now ready to be executed, and can be saved for later // execution if desired. // Invoke the closure. result = ((unsigned char(*)(float, unsigned int))closure)(42, 5.1); // Free the memory associated with the closure. if (munmap(closure, sizeof(closure)) == -1) { // Check errno and handle the error. } return 0; } // Invoking the closure transfers control to this function. static void foo_closure(ffi_cif* cif, void* result, void** args, void* userdata) { // Access the arguments to be sent to foo(). float arg1 = *(float*)args[0]; unsigned int arg2 = *(unsigned int*)args[1]; // Call foo() and save its return value. unsigned char ret_val = foo(arg1, arg2); // Copy the returned value into result. Because the return value of foo() // is smaller than sizeof(long), typecast it to ffi_arg. Use ffi_sarg // instead for signed types. *(ffi_arg*)result = (ffi_arg)ret_val; } // The closed-over function. unsigned char foo(unsigned int x, float y) { unsigned char result = x - y; return result; } SEE ALSO
ffi(3), ffi_prep_cif(3), mmap(2), munmap(2), mprotect(2) Darwin July 20, 2007 Darwin