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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW " title="NEW --- - [x86 assembler] no error diagnostic for out-of-range jrcxz/jecxz/jcxz" href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D24072&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=pF93YEPyB-J_PERP4DUZOJDzFVX5ZQ57vQk33wu0vio&m=H1fHg4b5rnP8m_DFsQaLV0J8R8Bk_1z6HooBzjQ4aEE&s=7QeaXFnTn0sNXJEcvO1zuV0eMkXGfLh9a8o-Z8uFi3w&e=">24072</a>
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<th>Summary</th>
<td>[x86 assembler] no error diagnostic for out-of-range jrcxz/jecxz/jcxz
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Windows NT
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>charles_li@playstation.sony.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>X86 instructions jrcxz/jecxz/jcxz performs short jumps if rcx/ecx/cx register
is 0
The maximum relative offset for a forward short jump is 127 Bytes (0x7F).
The maximum relative offset for a backward short jump is 128 Bytes (0x80).
Gnu assembler warns when the distance of the jump exceeds the maximum but
llvm-as does not.
Here are 3 examples:
/*******************************************************************/
<span class="quote">> cat jecxz.s</span >
.balign 256
jecxz foo
.balign 256
foo:
<span class="quote">> clang jecxz.s –c</span >
(no error)
<span class="quote">> gcc jecxz.s -c</span >
jecxz.s: Assembler messages:
jecxz.s:2: Error: value of 253 too large for field of 1 bytes at 2
/*******************************************************************/
<span class="quote">> cat jrcxz.s</span >
.balign 256
jrcxz foo
.balign 256
foo:
<span class="quote">> clang jrcxz.s -c -m64</span >
(no error)
<span class="quote">> gcc jrcxz.s -c -m64</span >
jrcxz.s: Assembler messages:
jrcxz.s:2: Error: value of 254 too large for field of 1 bytes at 1
/*******************************************************************/
<span class="quote">> cat jcxz.s</span >
.balign 256
jcxz foo
.balign 256
foo:
<span class="quote">> clang jcxz.s -c -m32</span >
(no error)
<span class="quote">> gcc jcxz.s -c -m32</span >
jcxz.s: Assembler messages:
jcxz.s:2: Error: value of 253 too large for field of 1 bytes at 2
/*******************************************************************/</pre>
</div>
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