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Data Bank Register management, part 5
Update documentation. Add some information about OMF relocation data as well. Fix bug in B=K handling.
This commit is contained in:
Andy McFadden
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0929077fda
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2a2aadffec
@ -1335,7 +1335,7 @@ namespace SourceGen {
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int bank;
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if (curVal == DbrValue.USE_PBR) {
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bank = mAnattribs[offset].Address >> 16;
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bank = mAnattribs[offset].Address & 0x00ff0000;
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} else {
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Debug.Assert(curVal >= 0 && curVal < 256);
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bank = curVal << 16;
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@ -301,6 +301,57 @@ address chunk, the first chunk that includes that address is used, as
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it is with the <code>JMP $1000</code> at the start of the file.</p>
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<h2><a name="reloc-data">OMF Relocation Dictionaries</a></h2>
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<p>65816 code can be tricky to disassemble for a number of reasons.
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24-bit addresses are formed from 16-bit data-access operands by combining
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with the Data Bank Register, which often requires a bit of manual
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intervention. But the problems go beyond that. Consider the following
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bit of source code for the Apple IIgs:</p>
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<pre>
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rsrcmsg pea rsrcmsg2|-16
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pea rsrcmsg2
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_WriteCString
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lda #buffer
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sta pArcRead+$04
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lda #buffer|-16
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sta pArcRead+$06
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</pre>
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<p>In both cases we're referencing a 24-bit address as two 16-bit values.
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Without context, the disassembler will treat the PEA instruction as two
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independent 16-bit addresses, and the immediate values as constants:</p>
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<pre>
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.dbank $02
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02/317c: f4 02 00 L2317C pea L20002 & $ffff
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02/317f: f4 54 32 pea L23254 & $ffff
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02/3182: a2 0c 20 ldx #WriteCString
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02/3185: 22 00 00 e1 jsl Toolbox
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02/3189: a9 00 00 L23189 lda #$0000
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02/318c: 8d 78 3f sta L23F78 & $ffff
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02/318f: a9 03 00 lda #$0003
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02/3192: 8d 7a 3f sta L23F78 & $ffff +2
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</pre>
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<p>Worse yet, those <code>STA</code> instruction operands would have been
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shown as hex values or incorrect labels if the DBR had been set incorrectly.
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However, if we have the relocation data, we know the full
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address from which the addresses were formed, and we can tell when
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immediate values are addresses rather than constants. And we can do this
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even without setting the DBR.</p>
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<pre>
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02/317c: f4 02 00 L2317C pea L23254 >> 16
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02/317f: f4 54 32 pea L23254 & $ffff
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02/3182: a2 0c 20 ldx #WriteCString
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02/3185: 22 00 00 e1 jsl Toolbox
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02/3189: a9 00 00 L23189 lda #L30000 & $ffff
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02/318c: 8d 78 3f sta L23F78 & $ffff
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02/318f: a9 03 00 lda #L30000 >> 16
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02/3192: 8d 7a 3f sta L23F78 & $ffff +2
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</pre>
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<p>This feature is still considered "experimental". There are some
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issues with it, e.g. the cross-reference table may show an incorrect
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offset.</p>
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<h2><a name="debug">Debug Menu Options</a></h2>
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<p>The DEBUG menu is hidden by default in release builds, but can be
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@ -305,6 +305,28 @@ not associated with a file offset. If you delete it, you can get it
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back by using Edit > Edit Header Comment.</p>
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<h2><a name="data-bank">Edit Data Bank (65816 only)</a></h2>
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<p>Sets the Data Bank Register (DBR) value for 65816 code. This is used
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when matching 16-bit address operands with labels. The new value is
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in effect from the line where it's declared to the end of the file, even
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across bank boundaries.
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If you leave the text field blank, the directive will be removed.</p>
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<p>A hexadecimal value from $00 to $ff can be entered directly. As
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with other address inputs, a leading '$' is not required. Entering
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"K" will set the DBR to the current address, and will automatically
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update if you change the address to a different bank.</p>
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<p>The pop-up menu has a list of all banks that hold code or data.
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To make them easier to identify, each is shown with the label on the
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first address in the bank, if any.</p>
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<p>While you can override automatically-generated data bank change
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directives, you can't remove them individually. You can disable
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automatic generation by un-checking "smart PLB handling" in the project
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properties.</p>
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<p>Because the directive is frequently associated with <code>PLB</code>
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instructions, double-clicking on a <code>PLB</code> opcode in the
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code list will open the editor.</p>
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<h2><a name="note">Edit Note</a></h2>
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<p>Notes are similar to long comments, in that they can be arbitrarily
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long and span multiple lines. However, because they're never included
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@ -35,6 +35,7 @@ and 65816 code. The official web site is
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<li><a href="intro.html#sgconcepts">SourceGen Concepts</a></li>
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<li><a href="intro.html#about-symbols">All About Symbols</a>
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<ul>
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<li><a href="intro.html#connecting-operands">Connecting Operands With Labels</a></li>
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<li><a href="intro.html#internal-address-symbols">Internal Address Symbols</a></li>
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<li><a href="intro.html#external-address-symbols">External Address Symbols</a></li>
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<li><a href="intro.html#unique-local-global">Unique vs. Non-Unique and Local vs. Global</a></li>
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@ -83,6 +84,7 @@ and 65816 code. The official web site is
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<li><a href="editors.html#data-operand">Edit Data Operand</a></li>
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<li><a href="editors.html#comment">Edit Comment</a></li>
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<li><a href="editors.html#long-comment">Edit Long Comment</a></li>
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<li><a href="editors.html#data-bank">Edit Data Bank (65816 only)</a></li>
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<li><a href="editors.html#note">Edit Note</a></li>
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<li><a href="editors.html#project-symbol">Edit Project Symbol</a></li>
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<li><a href="editors.html#lvtable">Edit Local Variable Table</a></li>
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@ -151,6 +153,7 @@ and 65816 code. The official web site is
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<li><a href="advanced.html#extension-scripts">Extension Scripts</a></li>
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<li><a href="advanced.html#multi-bin">Working With Multiple Binaries</a></li>
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<li><a href="advanced.html#overlap">Overlapping Address Spaces</a></li>
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<li><a href="advanced.html#reloc-data">OMF Relocation Dictionaries</a></li>
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<li><a href="advanced.html#debug">Debug Menu Options</a></li>
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</ul></li>
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@ -131,8 +131,8 @@ space, but it's not contiguous -- a branch that extends past the end will
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wrap around to the start of the 64KiB "bank". For 16-bit instruction
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operands, the bank is identified for instruction and data addresses
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by the program bank register and the data bank register, respectively.
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The disassembler can't generally know the contents of the data bank
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register, which makes life a bit more interesting.</p>
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The disassembler can't always discern the value of the data bank
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register through static analysis, so some user input may be required.</p>
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<p>The 6502 has an 8-bit processor status register ("P") with a bunch of flags
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in it. Some of the flags determine whether a conditional branch is taken
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@ -447,6 +447,35 @@ differently from those outside a project. We refer to these as internal
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and external addresses, respectively.</p>
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<h3><a name="connecting-operands">Connecting Operands with Labels</a></h3>
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<p>Suppose you have the following code:</p>
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<pre>
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LDA $1234
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JSR $2345
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</pre>
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<p>If we put that in a source file, it will assemble correctly.
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However, if those addresses are part of the file, the code may break if
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changes are made and things assemble to different addresses. It would
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be better to generate code that references labels, e.g.:</p>
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<pre>
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LDA my_data
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JSR nifty_func
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</pre>
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<p>SourceGen tries to establish labels for address operands automatically.
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How this works depends on whether the operand's address is inside the file or
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external, and whether there are existing labels at or near the target
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address. The details are explored in the next few sections.</p>
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<p>On the 65816 this process is trickier, because addresses are 24 bits
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instead of 16. For a control-transfer instruction like <code>JSR</code>,
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the high 8 bits come from the Program Bank Register (K). For a data-access
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instruction like <code>LDA</code>, the high 8 bits come from the Data
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Bank Register (B). The PBR value is determined by the address in which
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the code is executing, so it's easy to determine. The DBR value can be
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set arbitrarily. Sometimes it's easy to figure out, sometimes it has
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to be specified manually.</p>
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<h3><a name="internal-address-symbols">Internal Address Symbols</a></h3>
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<p>Symbols that represent an address inside the file being disassembled
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@ -889,6 +918,8 @@ code generator figure out the implementation details.</p>
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<li>.RWID - specifies the width of the accumulator and index registers
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(65816 only). Note this doesn't change the actual width, just tells
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the assembler that the width has changed.</li>
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<li>.DBANK - specifies what value the Data Bank Register holds
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(65816 only). Used when matching operands to labels.</li>
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<li>.JUNK - indicates that the data in a range of bytes is irrelevant.
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(When generating sources, this will become .FILL or .BULK
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depending on the contents of the memory region and the assembler's
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@ -105,9 +105,10 @@ files and libraries contain unresolved references and are not supported.</p>
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execute on an Apple IIgs. To be functional, the sources must be
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assembled by a program capable of generating OMF output, such as Merlin.</p>
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<p>The relocation dictionaries from the executable are included in the
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project file, and can be used to guide the disassembler's analysis. The
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"use reloc data" setting in the project properties controls this feature.</p>
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<p>The <a href="advanced.html#reloc-data">relocation dictionaries</a> from
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the executable are included in the project file, and can be used to guide
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the disassembler's analysis. The "use reloc data" setting in the project
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properties controls this feature.</p>
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<p>A full explanation of the structure of OMF is beyond the scope of this
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manual. For more information on OMF, see Appendix F of the GS/OS Reference
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@ -22,7 +22,7 @@ limitations under the License.
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xmlns:local="clr-namespace:SourceGen.WpfGui"
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xmlns:system="clr-namespace:System;assembly=mscorlib"
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mc:Ignorable="d"
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Title="Set Data Bank"
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Title="Edit Data Bank Register"
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SizeToContent="WidthAndHeight" ResizeMode="NoResize"
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ShowInTaskbar="False" WindowStartupLocation="CenterOwner"
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ContentRendered="Window_ContentRendered">
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