## Ruby/DL

an interface to dynamic linking loader

## Ruby/DL

`Ruby/DL' provides an interface to the dynamic linking loader.

## Installing

>     $ ruby extconf.rb    # to create the Makefile
>     $ make               # to build the library 'dl.so'
>     $ make libtest.so    # to build the C library 'libtest.so' for the test script
>     $ make test          # to run the test script
>     $ make install       # to install the library
>     $ make clean         # to remove the created files without Makefile
>     $ make distclean     # to remove the all created files

## Functions and Classes

after loading the `dl' library, we get access to the module called `DL'. the DL module has the following constants, functions and classes.

## Constants

VERSION
MAJOR_VERSION
MINOR_VERSION
PATCH_VERSION
RTLD_GLOBAL
RTLD_LAZY
RTLD_NOW
MAX_ARG
MAX_CBARG
MAX_CBENT

## Functions

handle = dlopen(lib){|handle| ... }
  is quite equal to `Handle.new(lib)'
sym = set_callback(cbtype, entry){|args| ... }
sym = set_callback(cbtype, entry, proc)
  makes entry-th pre-defined function to call the proc or given block. the entry-th pre-defined function is specified by cbtype and entry. cbtype is a prototype of the callback. see also the section `Type specifiers' about cbtype.
sym = get_callback(cbtype, entry)
  returns the Proc object which is given by the above function `set_callback'.
ptr = malloc(size, [free = nil])
  allocates the size bytes, and returns the pointer as a PtrData object ptr.
ptr = strdup(str)
  returns a PtrData object ptr which represents the pointer to a new string which is a duplicate of the string str.
size = sizeof(type)
  returns the size of type. `sizeof("C") + sizeof("L")' is not equal to `sizeof("CL")'. the latter is assumed to returns the enough size of the structure `struct foo { char c; long l; }', but the size may not equal to `sizeof(foo)' of C.

## class Handle

handle = Handle.new(lib){|handle| ... }
  opens a library lib and returns a Handle object handle. if a block is given, the handle is automatically closed as the block ends.
Handle#close
  closes the handle opened by the above Handle.new(lib).
sym = Handle#sym(func, prototype = "0")
sym = Handle#[func, prototype = nil]
  obtains the pointer to a function called func and returns a Symbol object or a DataPtr object. prototype is a string which consists of type specifiers, it indicates the function's prototype. see also the section `Type specifiers'.

## class Symbol

sym = Symbol.new(addr, type = nil, name = nil)
  creates the Symbol object sym with the type type if type is not nil. addr is the address where the function is allocated. If type is nil, it returns a DataPtr object.
Symbol::char2type(char)
  takes a character char that represents a type and returns the type specifier of the C language.
str = Symbol#proto()
  returns the function prototype.
str = Symbol#name()
  Returns the function name.
str = Symbol#cproto()
str = Symbol#to_s()
  returns the prototype of the C language.
str = Symbol#inspect()
  returns the inspectable string.
r,rs = Symbol#call(arg1,arg2,...,argN)
r,rs = Symbol#[](arg1,arg2,...,argN)
  calls the function with parameters arg1, arg2, ..., argN. and the result consists of the return value r and parameters rs. rs is an array.
ptr = Symbol#to_ptr
  returns the corresponding PtrData object ptr.

## class PtrData

ptr = PtrData.new(addr, [free = nil])
  returns the PtrData object representing the pointer which indicates the address addr. GC frees the memory using the free function.
PtrData#free=(sym)
  if you specify a symbol object sym, GC frees the memory using the function represented by sym.
sym = PtrData#free
  returns a symbol object sym which is used when GC frees the memory. it usually configured by `PtrData#free=' or `PtrData.new'.
size = PtrData#size, PtrData#size=(size)
  gets and sets allocated size of the memory.
ary = PtrData#to_a(type, [size])
  returns an array of the type which specified with type. type must be one of 'S','P','I','L','D' and 'F'.
str = PtrData#to_s([len])
  returns a string which length is len. if len is omitted, the end of the string is '\0'.
ptr = PtrData#ptr,+@
  returns the pointed value as a PtrData object ptr.
ptr = PtrData#ref,-@
  returns the reference as a PtrData object ptr.
ptr = PtrData#+
  returns the PtrData object
ptr = PtrData#-
  returns the PtrData object
PtrData#struct!(type, *members)
  defines the data type to get access to a structure member with a symbol. (see also PtrData#[])
PtrData#union!(type, *members)
  defines the data type to get access to a union member with a symbol. (see also PtrData#[])
val = PtrData#[key], PtrData#[key, num = 0]
  if the key is a string or symbol, this method returns the value of the structure/union member which has the type defined by PtrData#{struct!,union!}. if the key is a integer value and this object represents the pointer ptr, it returns the value of `(ptr + key).to_s(num)'
PtrData#[key,num]=val, PtrData#[key]=val
  if the key is a string or symbol, this method substitute the value of the structure/union member with val. if the key is a integer value and val is a string, this method copies num bytes of val to the memory area ptr using memcpy(3).

## Type specifiers

the prototype consists of the following type specifiers, first element of prototype represents the type of return value, and remaining elements represent the type of each argument.

> C : a character (char)
> c : a pointer to a character (char *)
> H : a short integer (short)
> h : a pointer to a short integer (short *)
> I : an integer (char, short, int)
> i : a pointer to an integer (char *, short *, int *)
> L : a long integer (long)
> l : a pointer to a long integer (long *)
> F : a real (float)
> f : a pointer to a real (float *)
> D : a real (double)
> d : a pointer to a real (double *)
> S : an immutable string (const char *)
> s : a mutable string (char *)
> A : an array (const type[])
> a : a mutable array (type[])
> P : a pointer (void *)
> p : a mutable object (void *)
> 0 : void function (this must be a first character of the prototype)

the cbtype consists of type specifiers 0, I, L, D and P.
for example:

>     DL.set_callback('IPP',0){|ptr1,ptr2|
>       str1 = ptr1.ptr.to_s
>       str2 = ptr2.ptr.to_s
>       return str1 <=> str2
>     }

ttate@kt.jaist.ac.jp