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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 --- - powerpc64 -fPIC missing required nop"
href="http://llvm.org/bugs/show_bug.cgi?id=17354">17354</a>
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</tr>
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<th>Summary</th>
<td>powerpc64 -fPIC missing required nop
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Backend: PowerPC
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>nlewycky@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>hfinkel@anl.gov, llvmbugs@cs.uiuc.edu
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Repro with "clang -target powerpc64-pc-linux-gnu test.ii -fPIC -S -o -",
testcase:
struct CS {
int a_;
};
CS func();
static CS glb[1] = {
func()
};
CS func() {
CS cs;
cs.a_ = 0;
return cs;
}
Clang generates the same assembly with and without -fPIC. GCC adds a 'nop'
after the call to func. Clang's asm does this:
[...]
.cfi_def_cfa_register r31
addis 3, 2, _ZL3glb@toc@ha
addi 3, 3, _ZL3glb@toc@l
bl _Z4funcv
addi 1, 1, 128
ld 0, 16(1)
ld 31, -8(1)
mtlr 0
blr
[...]
while GCC -fPIC emits:
[...]
cmpw 7,10,9
bne 7,.L3
addis 9,2,_ZL3glb@toc@ha
addi 9,9,_ZL3glb@toc@l
mr 3,9
bl _Z4funcv
nop
.L3:
addi 1,31,128
.cfi_def_cfa 1, 0
ld 0,16(1)
[...]
The linker (binutils gold 2.23.52.20130305) complains "other.cc:4: error: call
lacks nop, can't restore toc; recompile with -fPIC" when trying to link a final
program, after having built the code in the testcase into a .so.</pre>
</div>
</p>
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