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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Recent COFF dso_local changes break Firefox ThinLTO build"
href="https://bugs.llvm.org/show_bug.cgi?id=36686">36686</a>
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</tr>
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<th>Summary</th>
<td>Recent COFF dso_local changes break Firefox ThinLTO build
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</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>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>new bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>dmajor@mozilla.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, rafael@espindo.la
</td>
</tr></table>
<p>
<div>
<pre>Consider a library with a header that looks like this:
```
// MyLibrary.h
#ifdef BUILDING_MY_LIBRARY
#define MYAPI __declspec(dllexport)
#else
#define MYAPI __declspec(dllimport)
#endif
MYAPI MyFunc();
```
...and then in the same DLL where MyLibrary is implemented, there is also a
client of that library, which tries to dllimport MyFunc from its own DLL.
With link.exe we just get a warning LNK4049 and live with it. Same goes for
clang-cl with ThinLTO disabled, but when ThinLTO is enabled the build can't
continue.
------------------- Reproducer
$ cat a.cpp
__declspec(dllimport) int foo();
int main() { return foo(); }
$ cat b.cpp
__declspec(dllexport) int foo() { return 42; }
$ clang-cl -c -flto=thin a.cpp b.cpp
$ lld-link -nodefaultlib -entry:main a.obj b.obj
------------------- Before r325915/r325940:
lld-link: warning: lto.tmp: locally defined symbol imported: ?foo@@YAHXZ
(defined in lto.tmp)
------------------- After r325915/r325940:
GlobalValue with DLLImport Storage is dso_local!
i32 ()* @"\01?foo@@YAHXZ"
LLVM ERROR: Broken module found, compilation aborted!</pre>
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