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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - PowerPC64: function calls missing relocations in PIC codegen when the callee is defined in same CU."
href="https://bugs.llvm.org/show_bug.cgi?id=39080">39080</a>
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<th>Summary</th>
<td>PowerPC64: function calls missing relocations in PIC codegen when the callee is defined in same CU.
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>Other
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: PowerPC
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>sfertile@ca.ibm.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>When compiling a file for a shared object (-fpic and not -fPIE) we need to emit
a relocation for calls where the callee is interposable. When the callee is
defined in the same translation unit we fail to do this.
eg:
test.c:
__attribute__((noinline))
int defined(int i) {
return i;
}
int a = 55;
int caller(void) {
return defined (a);
}
clang -O2 -c -fpic test.c
objdump -Dr test.o | less
0000000000000000 <defined>:
0: 20 00 80 4e blr
...
0000000000000010 <caller>:
10: 00 00 4c 3c addis r2,r12,0
10: R_PPC64_REL16_HA .TOC.
14: 00 00 42 38 addi r2,r2,0
14: R_PPC64_REL16_LO .TOC.+0x4
18: a6 02 08 7c mflr r0
1c: 10 00 01 f8 std r0,16(r1)
20: e1 ff 21 f8 stdu r1,-32(r1)
24: 00 00 62 3c addis r3,r2,0
24: R_PPC64_TOC16_HA .toc
28: 00 00 63 e8 ld r3,0(r3)
28: R_PPC64_TOC16_LO_DS .toc
2c: 02 00 63 e8 lwa r3,0(r3)
30: d1 ff ff 4b bl 0 <defined>
34: 00 00 00 60 nop
38: 20 00 21 38 addi r1,r1,32
3c: 10 00 01 e8 ld r0,16(r1)
40: a6 03 08 7c mtlr r0
44: 20 00 80 4e blr
Instead of having a relocation to defined, the bl instruction already has the
offset immediate encoded in it `4bffffd1` = `bl -0x30`. This means the linker
will never create a plt stub for the call and if the dynamic linker resolves a
different definition of `defined` at runtime some calls will be redirect to
that definition while others will still call this definition.
It can be worked around by using the `--function-sections` option as we emit
the relocation in that case:
20: 01 00 00 48 bl 20 <caller+0x20>
20: R_PPC64_REL24 defined</pre>
</div>
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