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<h2 class="chapter">1 What is libffi?</h2>
<p>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 <dfn>calling
convention</dfn>. 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 <dfn>ABI</dfn> or <dfn>Application Binary Interface</dfn>.
<a name="index-calling-convention-1"></a><a name="index-ABI-2"></a><a name="index-Application-Binary-Interface-3"></a>
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. ‘<samp><span class="samp">Libffi</span></samp>’ can be used in such programs to
provide a bridge from the interpreter program to compiled code.
<p>The ‘<samp><span class="samp">libffi</span></samp>’ 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.
<p><acronym>FFI</acronym> 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 ‘<samp><span class="samp">libffi</span></samp>’ library really only provides the lowest, machine
dependent layer of a fully featured foreign function interface. A
layer must exist above ‘<samp><span class="samp">libffi</span></samp>’ that handles type conversions for
values passed between the two languages.
<a name="index-FFI-4"></a><a name="index-Foreign-Function-Interface-5"></a>
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