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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Undefined symbol with CFI and __attribute__((__used__))"
href="https://bugs.llvm.org/show_bug.cgi?id=49251">49251</a>
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<th>Summary</th>
<td>Undefined symbol with CFI and __attribute__((__used__))
</td>
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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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>new bugs
</td>
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<th>Assignee</th>
<td>tejohnson@google.com
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<th>Reporter</th>
<td>samitolvanen@google.com
</td>
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<th>CC</th>
<td>htmldeveloper@gmail.com, i@maskray.me, llvm-bugs@lists.llvm.org, ndesaulniers@google.com, peter@pcc.me.uk
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<p>
<div>
<pre>Commit rG3c4c205060c9 ("[WPD][lld] Test handling of vtable definition from
shared libraries") breaks my Linux kernel build with ThinLTO and CFI, because
the compiler now generates an undefined symbol in a kernel module for a static
function with __attribute__((__used__)).
A stand-alone reproducer:
$ cat test.c
static __attribute__((__used__)) f1() {}
f2() {}
$ clang -flto=thin -fsanitize=cfi -fvisibility=default -O2 -c -o test.o test.c
...
$ ld.lld -r -o test.lto.o test.o
$ readelf --symbols test.lto.o | grep f1
9: 0000000000000000 1 FUNC GLOBAL HIDDEN 4
f1$0c315d2ea609b3d583650e385e8cf855
11: 0000000000000000 0 NOTYPE GLOBAL DEFAULT UND f1
Before this commit, the undefined symbol wasn't generated:
$ readelf --symbols test.lto.o | grep f1
9: 0000000000000000 1 FUNC GLOBAL HIDDEN 4
f1$0c315d2ea609b3d583650e385e8cf855</pre>
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