<html>
<head>
<base href="https://bugs.llvm.org/">
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - lld + ThinLTO + fprofile-generate causes duplicate symbol errors"
href="https://bugs.llvm.org/show_bug.cgi?id=37422">37422</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>lld + ThinLTO + fprofile-generate causes duplicate symbol errors
</td>
</tr>
<tr>
<th>Product</th>
<td>tools
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>lto
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>pirama@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Filing issue reported in llvm-dev thread
<a href="http://lists.llvm.org/pipermail/llvm-dev/2018-May/123131.html">http://lists.llvm.org/pipermail/llvm-dev/2018-May/123131.html</a>.
The duplicate symbol errors are for __llvm_profile_filename and
__llvm_profile_raw_version. IIUC, these are supposed to be weak symbols but
Thin LTO seems to break this in some way. This does't happen with gold or no
LTO or full LTO.
$ cat > a.c
extern int foo();
int main() {
return foo();
}
$ cat > b.c
int foo() {
return 0;
}
$ clang a.c -fprofile-generate -flto=thin -c
$ clang b.c -fprofile-generate -flto=thin -c
$ clang a.o b.o -fprofile-generate -flto=thin -fuse-ld=lld
ld.lld: error: duplicate symbol: __llvm_profile_filename
<span class="quote">>>> defined at a.c
>>> lto.tmp:(__llvm_profile_filename)
>>> defined at b.c
>>> lto.tmp:(.rodata.__llvm_profile_filename+0x0)</span >
ld.lld: error: duplicate symbol: __llvm_profile_raw_version
<span class="quote">>>> defined at a.c
>>> lto.tmp:(__llvm_profile_raw_version)
>>> defined at b.c
>>> lto.tmp:(.rodata.__llvm_profile_raw_version+0x0)</span >
clang-7: error: linker command failed with exit code 1 (use -v to see
invocation)
Teresa Johnson>> From adding save-temps, it looks like lld and gold are giving
different resolutions to the symbols, which is presumably creating this issue:
Peter Collingbourne>> The problem is that ThinLTO is not dropping the
non-prevailing definitions, and they end up being emitted into the object file
for b.o.
$ ../ra/bin/llvm-dis -o - b.o0.0.preopt.bc | grep __llvm_prof
$__llvm_profile_raw_version = comdat any
$__llvm_profile_filename = comdat any
@__llvm_profile_raw_version = constant i64 72057594037927940, comdat
@__llvm_profile_filename = constant [19 x i8] c"default_%m.profraw\00", comdat
lld ignores comdats in LTO object files because it expects all comdats to have
already been resolved. So we see this error.
We are supposed to drop non-prevailing symbols here, but for some reason we do
it only for weak symbols. That's not correct in ELF where comdat symbols can be
both strong and non-prevailing.
<a href="http://llvm-cs.pcc.me.uk/lib/LTO/LTO.cpp#290">http://llvm-cs.pcc.me.uk/lib/LTO/LTO.cpp#290</a>
This patch fixes the reproducer but it leads to other test failures that would
need to be looked at.
diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
index 7e8b9b3c6390..ee11d07d6b8e 100644
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -287,7 +287,7 @@ static void thinLTOResolveWeakForLinkerGUID(
recordNewLinkage) {
for (auto &S : GVSummaryList) {
GlobalValue::LinkageTypes OriginalLinkage = S->linkage();
- if (!GlobalValue::isWeakForLinker(OriginalLinkage))
+ if (GlobalValue::isLocalLinkage(OriginalLinkage))
continue;
// We need to emit only one of these. The prevailing module will keep it,
// but turned into a weak, while the others will drop it when possible.
diff --git a/llvm/lib/Transforms/IPO/FunctionImport.cpp
b/llvm/lib/Transforms/IPO/FunctionImport.cpp
index 246d75caefa2..61790c9fc435 100644
--- a/llvm/lib/Transforms/IPO/FunctionImport.cpp
+++ b/llvm/lib/Transforms/IPO/FunctionImport.cpp
@@ -765,7 +765,7 @@ void llvm::thinLTOResolveWeakForLinkerModule(
return;
}
- if (!GlobalValue::isWeakForLinker(GV.getLinkage()))
+ if (GlobalValue::isLocalLinkage(GV.getLinkage()))
return;
// Check for a non-prevailing def that has interposable linkage
// (e.g. non-odr weak or linkonce). In that case we can't simply</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>