148 lines
7 KiB
HTML
148 lines
7 KiB
HTML
<!DOCTYPE html>
|
|
<html>
|
|
<!-- Created by GNU Texinfo 7.1, https://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<!-- This manual documents Guile version 3.0.10.
|
|
|
|
Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
|
|
Inc.
|
|
|
|
Copyright (C) 2021 Maxime Devos
|
|
|
|
Copyright (C) 2024 Tomas Volf
|
|
|
|
|
|
Permission is granted to copy, distribute and/or modify this document
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
|
any later version published by the Free Software Foundation; with no
|
|
Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
|
|
copy of the license is included in the section entitled "GNU Free
|
|
Documentation License." -->
|
|
<title>Stack Layout (Guile Reference Manual)</title>
|
|
|
|
<meta name="description" content="Stack Layout (Guile Reference Manual)">
|
|
<meta name="keywords" content="Stack Layout (Guile Reference Manual)">
|
|
<meta name="resource-type" content="document">
|
|
<meta name="distribution" content="global">
|
|
<meta name="Generator" content=".texi2any-real">
|
|
<meta name="viewport" content="width=device-width,initial-scale=1">
|
|
|
|
<link href="index.html" rel="start" title="Top">
|
|
<link href="Concept-Index.html" rel="index" title="Concept Index">
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|
<link href="A-Virtual-Machine-for-Guile.html" rel="up" title="A Virtual Machine for Guile">
|
|
<link href="Variables-and-the-VM.html" rel="next" title="Variables and the VM">
|
|
<link href="VM-Concepts.html" rel="prev" title="VM Concepts">
|
|
<style type="text/css">
|
|
<!--
|
|
a.copiable-link {visibility: hidden; text-decoration: none; line-height: 0em}
|
|
div.example {margin-left: 3.2em}
|
|
span:hover a.copiable-link {visibility: visible}
|
|
-->
|
|
</style>
|
|
<link rel="stylesheet" type="text/css" href="https://www.gnu.org/software/gnulib/manual.css">
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en">
|
|
<div class="subsection-level-extent" id="Stack-Layout">
|
|
<div class="nav-panel">
|
|
<p>
|
|
Next: <a href="Variables-and-the-VM.html" accesskey="n" rel="next">Variables and the VM</a>, Previous: <a href="VM-Concepts.html" accesskey="p" rel="prev">VM Concepts</a>, Up: <a href="A-Virtual-Machine-for-Guile.html" accesskey="u" rel="up">A Virtual Machine for Guile</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
<hr>
|
|
<h4 class="subsection" id="Stack-Layout-1"><span>9.3.3 Stack Layout<a class="copiable-link" href="#Stack-Layout-1"> ¶</a></span></h4>
|
|
|
|
<p>The stack of Guile’s virtual machine is composed of <em class="dfn">frames</em>. Each
|
|
frame corresponds to the application of one compiled procedure, and
|
|
contains storage space for arguments, local variables, and some
|
|
bookkeeping information (such as what to do after the frame is
|
|
finished).
|
|
</p>
|
|
<p>While the compiler is free to do whatever it wants to, as long as the
|
|
semantics of a computation are preserved, in practice every time you
|
|
call a function, a new frame is created. (The notable exception of
|
|
course is the tail call case, see <a class="pxref" href="Tail-Calls.html">Tail calls</a>.)
|
|
</p>
|
|
<p>The structure of the top stack frame is as follows:
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example-preformatted"> | ...previous frame locals... |
|
|
+==============================+ <- fp + 3
|
|
| Dynamic link |
|
|
+------------------------------+
|
|
| Virtual return address (vRA) |
|
|
+------------------------------+
|
|
| Machine return address (mRA) |
|
|
+==============================+ <- fp
|
|
| Local 0 |
|
|
+------------------------------+
|
|
| Local 1 |
|
|
+------------------------------+
|
|
| ... |
|
|
+------------------------------+
|
|
| Local N-1 |
|
|
\------------------------------/ <- sp
|
|
</pre></div>
|
|
|
|
<p>In the above drawing, the stack grows downward. At the beginning of a
|
|
function call, the procedure being applied is in local 0, followed by
|
|
the arguments from local 1. After the procedure checks that it is being
|
|
passed a compatible set of arguments, the procedure allocates some
|
|
additional space in the frame to hold variables local to the function.
|
|
</p>
|
|
<p>Note that once a value in a local variable slot is no longer needed,
|
|
Guile is free to re-use that slot. This applies to the slots that were
|
|
initially used for the callee and arguments, too. For this reason,
|
|
backtraces in Guile aren’t always able to show all of the arguments: it
|
|
could be that the slot corresponding to that argument was re-used by
|
|
some other variable.
|
|
</p>
|
|
<p>The <em class="dfn">virtual return address</em> is the <code class="code">ip</code> that was in effect
|
|
before this program was applied. When we return from this activation
|
|
frame, we will jump back to this <code class="code">ip</code>. Likewise, the <em class="dfn">dynamic
|
|
link</em> is the offset of the <code class="code">fp</code> that was in effect before this
|
|
program was applied, relative to the current <code class="code">fp</code>.
|
|
</p>
|
|
<p>There are two return addresses: the virtual return address (vRA), and
|
|
the machine return address (mRA). The vRA is always present and
|
|
indicates a bytecode address. The mRA is only present when a call is
|
|
made from a function with machine code (e.g. a function that has been
|
|
JIT-compiled).
|
|
</p>
|
|
<p>To prepare for a non-tail application, Guile’s VM will emit code that
|
|
shuffles the function to apply and its arguments into appropriate stack
|
|
slots, with three free slots below them. The call then initializes
|
|
those free slots to hold the machine return address (or NULL), the
|
|
virtual return address, and the offset to the previous frame pointer
|
|
(<code class="code">fp</code>). It then gets the <code class="code">ip</code> for the function being called
|
|
and adjusts <code class="code">fp</code> to point to the new call frame.
|
|
</p>
|
|
<p>In this way, the dynamic link links the current frame to the previous
|
|
frame. Computing a stack trace involves traversing these frames.
|
|
</p>
|
|
<p>Each stack local in Guile is 64 bits wide, even on 32-bit architectures.
|
|
This allows Guile to preserve its uniform treatment of stack locals
|
|
while allowing for unboxed arithmetic on 64-bit integers and
|
|
floating-point numbers. See <a class="xref" href="Instruction-Set.html">Instruction Set</a>, for more on unboxed
|
|
arithmetic.
|
|
</p>
|
|
<p>As an implementation detail, we actually store the dynamic link as an
|
|
offset and not an absolute value because the stack can move at runtime
|
|
as it expands or during partial continuation calls. If it were an
|
|
absolute value, we would have to walk the frames, relocating frame
|
|
pointers.
|
|
</p>
|
|
</div>
|
|
<hr>
|
|
<div class="nav-panel">
|
|
<p>
|
|
Next: <a href="Variables-and-the-VM.html">Variables and the VM</a>, Previous: <a href="VM-Concepts.html">VM Concepts</a>, Up: <a href="A-Virtual-Machine-for-Guile.html">A Virtual Machine for Guile</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|