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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - COFF line table debug info is wrong in the presence of __asm align 4"
href="http://llvm.org/bugs/show_bug.cgi?id=18679">18679</a>
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<th>Summary</th>
<td>COFF line table debug info is wrong in the presence of __asm align 4
</td>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>DebugInfo
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>timurrrr@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>See test/DebugInfo/COFF/asm.ll:
; 1 void g(void);
; 2
; 3 void f(void) {
; 4 __asm align 4;
; 5 g();
; 6 }
Generates this code:
+0: calll _g
+5: ret
There's the following problem at debug info generation time.
The debug line table format is something like:
...
<number of lines>
...
<pc><line>
<pc><line>
...
<pc><line>
...
For each instruction on a new source code line, WinCodeViewLineTables generates
a new entry in the debug info.
The problem is that "__asm align 4" doesn't generate any code in the result
binary.
So for the above example the table looks like this:
...
3
...
+0x0 4
+0x0 5
+0x5 6
...
If a stack trace includes 'f' calling 'g', the symbolizer looks up '+0x0' in
the debug info line table and gets line 4 as the result. Thus, the line number
in the symbolized stack trace is wrong.
Is there a way to know whether a particular instruction generates any bytes?
It'd be very handy to just skip processing of such an __asm block while
generating the debug info.</pre>
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