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@ -48,8 +48,12 @@ void f() {}
This empty function will be mangled to <code>_Z1fv</code>. The This empty function will be mangled to <code>_Z1fv</code>. The
<code>1f</code> signifies the name (we will look at this in more <code>1f</code> signifies the name (we will look at this in more
detail later in this lesson) and the <code>v</code> signifies the detail later in this lesson) and the <code>v</code> signifies the
function type (which we will visit in more detail in a future function type.
lesson). </p>
<p>
We will see the <code>v</code> function type a lot in the rest of
this guide. It stands for a function that takes no arguments and
returns <code>void</code>.
</p> </p>
<div class="quiz-section"> <div class="quiz-section">
<p> <p>
@ -79,9 +83,31 @@ void f() {}
</div> </div>
</section> </section>
<section data-step="1" class="step"> <section data-step="1" class="step">
<p></p> <p>
For names, there are two cases to consider for now. Either the name
is in the global scope, or it is in a namespace.
</p>
<p>For global names, we just prefix the name with its length.</p>
<pre class="code">
void hello_world() {}
</pre>
<p>
This will therefore get mangled as <code>_Z11hello_worldv</code>.
The length of <code>hello_world</code> is 11, so we concatenate
<code>11</code> and <code>hello_world</code>. This entire thing is
then appended to the previously mentioned prefix <code>_Z</code> and
then we add the type, which is just <code>v</code> here, at the end.
</p>
<div class="quiz-section"> <div class="quiz-section">
<form data-challenge="2" data-answer="meow"> <p>What is the mangling of the following identifier?</p>
<pre class="code">
void meow() {}
</pre>
<form
data-challenge="2"
data-answer="_Z4meowv"
data-hint="Remember the prefix and function type"
>
<input class="quiz-input" /> <input class="quiz-input" />
<button <button
data-challenge-submit="2" data-challenge-submit="2"
@ -94,6 +120,109 @@ void f() {}
</form> </form>
</div> </div>
</section> </section>
<section data-step="2" class="step">
<p>
Functions that are declared in a namespace get a bit more
complicated. They are referred to as <i>nested names</i>, because
they are <i>nested</i> in a namespace. They can also be nested in
multiple namespaces, the encoding is the same.
</p>
<p>
Nested names start with an <code>N</code> and end with an
<code>E</code>. Between those two letters, the hierarchy of the
namespace is represented by putting on namespace name after another,
with the function name last. Every name has the leading length and
then the name itself, just like with global names.
</p>
<pre class="code">
namespace outer {
void inner() {}
}
</pre>
<p>
That means that this function will be mangled as
<code>_ZN5outer5innerEv</code>. We can decode this into the
following structure
</p>
<ul>
<li><code>_Z</code>: Prefix</li>
<li><code>N</code>: Start of nested name</li>
<li>
<code>5outer</code>: Outer namespace, name prefixed by length
</li>
<li>
<code>5inner</code>: Inner function, name prefixed by length
</li>
<li><code>E</code>: End of nested name</li>
<li><code>v</code>: Function type</li>
</ul>
<p>Nested namespaces follow the same structure.</p>
<pre class="code">
namespace a {
namespace b {
namespace c {
void inner() {}
}
}
}
</pre>
<p>
This function will mangle as <code>_ZN1a1b1c5innerEv</code>. We get
all the concatinated names as <code>1a1b1c5inner</code>, with the
previously mentioned characters around them.
</p>
<div class="quiz-section">
<p>What is the mangling of the following identifier?</p>
<pre class="code">
namespace cats {
namespace like {
void meow() {}
}
}
</pre>
<form
data-challenge="3"
data-answer="_ZN4cats4like4meowEv"
data-hint="Remember the prefix and function type, and don't forget to wrap it in the nested start and end"
>
<input class="quiz-input" />
<button
data-challenge-submit="3"
class="submit-challenge"
type="submit"
>
Answer
</button>
<div class="error"></div>
</form>
</div>
</section>
<section data-step="3" class="step">
<p>
Good job! You have successfully answered all the question and now
know the basic makeup of an Itanium-mangled C++ symbol.
</p>
<p>
In the next lesson, we will use this knowledge to look at basic
function types beyond <code>v</code>. Mangling function types is
important for function overloading, but I don't want to overload you
with information, so feel free to take a break and let the previous
knowledge sink in.
</p>
<p>
If you want to try out more code and look at its mangling, I
recommend using Compiler Explorer on
<a href="https://godbolt.org">godbolt.org</a>. Under "Output", you
can uncheck the box to demangle identifiers to see the mangled
identifiers for any C++ code you enter on the left.
</p>
<div class="center">
<a href="/lesson-2.html" class="action-button">
Lesson 2: something that has not been written yet.
</a>
</div>
</section>
</div> </div>
</main> </main>
<script> <script>