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8c5509d69d
The tutorial was creating a new address region at +000002 without removing the previous one, which leaves the 16-bit file load address sitting at $1000 when it should be non-addressable. The text now shows the correct procedure. Some screen shots had to be recaptured to show the greyed-out address field. This doesn't change anything meaningful about the disassembly -- the PRG optimization hides the region start/end markers either way -- but it's more correct this way, and it's an opportunity to introduce the use of non-addressable regions for file headers.
226 lines
9.3 KiB
HTML
226 lines
9.3 KiB
HTML
<!DOCTYPE html>
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<html lang="en">
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<head>
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<title>Digging Deeper - SourceGen Tutorial</title>
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<body>
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<div id="masthead">
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<!--<div class="masthead-title" style="background-image: url('images/screenshot-mainwin.png');">-->
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<div class="masthead-title">
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6502bench
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</div>
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<!-- START: /incl-topnav.html active:#topnav-sgtutorial -->
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<div id="topnav">
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<nav>
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<a id="topnav-home" href=".././">HOME</a>
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<a id="topnav-sgtutorial" class="active" href="../sgtutorial">SourceGen Tutorial</a>
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<a id="topnav-menuicon" href="javascript:void(0);" class="icon" onclick="toggleSidenav()">
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<script>
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// Sidenav toggle function.
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//
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// Use a jQuery function to toggle the sidenav bar. The initial state
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// is undefined / inherited, so it will pop in and out as the screen
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// resizes around the "large" breakpoint.
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function toggleSidenav() {
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$("#sidenav").toggle("fast");
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}
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</div>
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<!-- START: incl-sidenav.html active:#sidenav-digging-deeper -->
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<div id="sidenav">
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<ul>
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<li id="sidenav-index"><a href="./">Introduction</a></li>
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<li id="sidenav-about-disasm"><a href="about-disasm.html">About Disassembly</a></li>
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<li id="sidenav-using-sourcegen"><a href="using-sourcegen.html">Using SourceGen</a>
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<ul>
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<li id="sidenav-moving-around"><a href="moving-around.html">Moving Around</a></li>
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<li id="sidenav-making-edits"><a href="making-edits.html">Making Edits</a></li>
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<li id="sidenav-labels-symbols"><a href="labels-symbols.html">Labels & Symbols</a></li>
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<li id="sidenav-editing-data"><a href="editing-data.html">Editing Data Operands</a></li>
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<li id="sidenav-generating-code"><a href="generating-code.html">Generating Code</a></li>
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</ul></li>
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<li id="sidenav-digging-deeper" class="active"><a href="digging-deeper.html">Digging Deeper</a>
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<ul>
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<li id="sidenav-string-formatting"><a href="string-formatting.html">String Formatting</a></li>
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<li id="sidenav-local-variables"><a href="local-variables.html">Local Variables</a></li>
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<li id="sidenav-inline-data"><a href="inline-data.html">Inline Data</a></li>
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<li id="sidenav-odds-ends"><a href="odds-ends.html">Odds & Ends</a></li>
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</ul></li>
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<ul>
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<li id="sidenav-address-tables"><a href="address-tables.html">Address Tables</a></li>
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<li id="sidenav-extension-scripts"><a href="extension-scripts.html">Extension Scripts</a></li>
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<li id="sidenav-visualizations"><a href="visualizations.html">Visualizations</a></li>
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</ul></li>
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<li id="sidenav-suggestions"><a href="suggestions.html">Suggestions</a></li>
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<div id="main">
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<h2>Digging Deeper</h2>
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<div class="grid-container">
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<div class="grid-item-text">
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<p>This tutorial will walk you through some of the fancier things SourceGen
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can do. We assume you've already finished the basic features tutorial,
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and know how to create projects and move around in them.</p>
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<p>Start a new project. Select <samp>Generic 6502</samp>. For the
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data file, navigate to the Examples directory, then from the Tutorial
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directory select "Tutorial2".</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t2-tutorial-top.png" alt="t2-tutorial-top"/>
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</div>
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<div class="grid-item-text">
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<p>Looking at the code list, the first thing you'll notice is that we
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immediately ran into a
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<code>BRK</code>, which is a pretty reliable sign that we're not in
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a code section. This particular file begins with <code>00 20</code>, which
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could be a load address (e.g. some C64 binaries look like this). So let's start
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with that assumption.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-text">
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<p>As discussed in the introductory material, SourceGen separates code
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from data by tracing all possible execution paths from declared entry
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points. The generic profiles mark the first byte of the file as an entry
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point, but that's wrong here. We want to change the entry point to
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be after the 16-bit load address, at offset +000002.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t2-1000-edit1.png" alt="t2-1000-edit1"/>
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</div>
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<div class="grid-item-text">
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<p>Click on the first line of code at address $1000, and select
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<samp>Actions > Remove Analyzer Tags</samp>
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(<kbd class="key">Ctrl+H</kbd> <kbd class="key">Ctrl+R</kbd>).
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This removes the "code start point" tag.
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Then, click on the <code>.addrs</code> line above it, and select
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<samp>Actions > Create / Edit Address Region</samp>. Down
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at the bottom, click <samp>Delete Region</samp>. This
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removes the default address region, replacing it with one that
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says "<code>NA</code>", meaning that the code is non-addressable.
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This is correct for the first two bytes, which will be
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read by the system loader but not actually loaded into memory.
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We still need to create a new address region at offset +000002.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t2-1000-edit2.png" alt="t2-1000-edit2"/>
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</div>
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<div class="grid-item-text">
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<p>Unfortunately the $20 is still auto-detected as being part
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of a string directive, which is making it hard to manipulate
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the next few bytes.
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Let's fix that by selecting <samp>Edit > Toggle Data Scan</samp>
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(<kbd class="key">Ctrl+D</kbd>). This turns off the feature that
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automatically generates string and <code>.FILL</code> directives,
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so now each uncategorized byte is on its own line.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t2-1000-fmt-word.png" alt="t2-1000-fmt-word"/>
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</div>
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<div class="grid-item-text">
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<p>You could select the first two lines and use
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<samp>Actions > Edit Operand</samp> to format them as a 16-bit
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little-endian hex value, but there's a shortcut: select the first
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line with data (offset +000000), then
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<samp>Actions > Format As Word</samp>
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(<kbd class="key">Ctrl+W</kbd>).
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It automatically grabbed the following byte and combined them.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t2-1000-setcode.png" alt="t2-1000-setcode"/>
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</div>
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<div class="grid-item-text">
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<p>Since we currently believe $2000 is the load address for everything
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that follows, click on the line with offset +000002, select
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<samp>Actions > Create/Edit Address Region</samp>, and enter "2000"
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for the address. Click <samp>OK</samp>.
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With that line still selected, use
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<samp>Actions > Tag Address As Code Start Point</samp>
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(<kbd class="key">Ctrl+H</kbd> <kbd class="key">Ctrl+C</kbd>) to
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tell the analyzer to start looking for code there.</p>
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</div>
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</div>
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<div class="grid-container">
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<div class="grid-item-image">
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<img src="images/t2-1000-ready.png" alt="t2-1000-ready"/>
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</div>
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<div class="grid-item-text">
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<p>That looks better, but the branch destination ($203D) is off the bottom of the
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screen (unless you have a really tall screen or small fonts) because of
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all the intervening data. Use <samp>Edit > Toggle Data Scan</samp>
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(<kbd class="key">Ctrl+D</kbd>)
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to turn the string-finder back on. Now it's easier to read.</p>
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</div>
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</div>
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</div> <!-- #main -->
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