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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 - Debug info generates undefined reference for template value which causes linker failure"
href="https://bugs.llvm.org/show_bug.cgi?id=40307">40307</a>
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<th>Summary</th>
<td>Debug info generates undefined reference for template value which causes linker failure
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<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>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>DebugInfo
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>brock.wyma@intel.com
</td>
</tr>
<tr>
<th>CC</th>
<td>jdevlieghere@apple.com, keith.walker@arm.com, llvm-bugs@lists.llvm.org, paul_robinson@playstation.sony.com
</td>
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<p>
<div>
<pre>$ cat global-template-value.cpp
template <const char* U> struct One {
static const char string [4];
};
int main() {
One< One<nullptr>::string > one;
return 0;
}
The GNU compiler compiles/links this code and produces debug information for
the template value parameter "U" with no location:
$ g++ -g global-template-value.cpp
$ readelf -wi a.out
...
<2><6e>: Abbrev Number: 8 (DW_TAG_template_value_param)
<6f> DW_AT_name : U
<71> DW_AT_type : <0xaf>
...
With no debug information CLANG compiles/links the code with a helpful warning
message:
$ clang++ global-template-value.cpp
global-template-value.cpp:6:22: warning: instantiation of variable
'One<nullptr>::string' required here, but no definition is available
[-Wundefined-var-template]
One< One<nullptr>::string > one;
^
global-template-value.cpp:2:21: note: forward declaration of template entity is
here
static const char string [4];
^
global-template-value.cpp:6:22: note: add an explicit instantiation declaration
to
suppress this warning if 'One<nullptr>::string' is explicitly
instantiated
in another translation unit
One< One<nullptr>::string > one;
^
1 warning generated.
But when debug information is enabled CLANG fails to link:
$ clang++ -g global-template-value.cpp
...
/tmp/global-template-value-5c4370.o:(.debug_info+0x78): undefined reference to
`One<(char const*)0>::string'
clang-8: error: linker command failed with exit code 1 (use -v to see
invocation)
The linker failure is caused because of a global variable reference in the
debug metadata here:
!21 = !DITemplateValueParameter(name: "U", type: !22, value: [4 x i8]*
@_ZN3OneILPKc0EE6stringE)
Obviously if the global had been defined in the source then the debug
information would link correctly, but it seems more friendly to emit the
DW_TAG_template_value_param with no location like GCC does.</pre>
</div>
</p>
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