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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - libomp.so: Missing linking against libm.so when compiled by Clang on Linux systems"
href="https://bugs.llvm.org/show_bug.cgi?id=52115">52115</a>
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<th>Summary</th>
<td>libomp.so: Missing linking against libm.so when compiled by Clang on Linux systems
</td>
</tr>
<tr>
<th>Product</th>
<td>OpenMP
</td>
</tr>
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<th>Version</th>
<td>unspecified
</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>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Runtime Library
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>arfrever.fta@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Gentoo report: <a href="https://bugs.gentoo.org/816831">https://bugs.gentoo.org/816831</a>
As reported there, libomp.so compiled by Clang (instead of GCC) uses at least
fmaxl, which is defined in libm.so, but build system does not pass -lm to
consider linking against libm.so.
<span class="quote">> $ nm -D /usr/lib64/libomp.so | grep fmaxl
> U fmaxl
> $ readelf -d /usr/lib64/libomp.so | grep NEEDED
> 0x0000000000000001 (NEEDED) Shared library: [libpthread.so.0]
> 0x0000000000000001 (NEEDED) Shared library: [librt.so.1]
> 0x0000000000000001 (NEEDED) Shared library: [libdl.so.2]
> 0x0000000000000001 (NEEDED) Shared library: [libc.so.6]
> 0x0000000000000001 (NEEDED) Shared library: [ld-linux-x86-64.so.2]</span >
<a href="https://github.com/llvm/llvm-project/blob/37109974af4b33189a599735afa67ed57c27b8ab/openmp/runtime/cmake/LibompHandleFlags.cmake#L138-L144">https://github.com/llvm/llvm-project/blob/37109974af4b33189a599735afa67ed57c27b8ab/openmp/runtime/cmake/LibompHandleFlags.cmake#L138-L144</a>
contains:
<span class="quote">> if(${CMAKE_SYSTEM_NAME} MATCHES "DragonFly|FreeBSD")
> libomp_append(libflags_local "-Wl,--no-as-needed" LIBOMP_HAVE_AS_NEEDED_FLAG)
> libomp_append(libflags_local "-lm")
> libomp_append(libflags_local "-Wl,--as-needed" LIBOMP_HAVE_AS_NEEDED_FLAG)
> elseif(${CMAKE_SYSTEM_NAME} MATCHES "NetBSD")
> libomp_append(libflags_local -lm)
> endif()</span >
I do not know why this code uses --no-as-needed to forcefully link against
libm.so on DragonFly and FreeBSD, but I am not asking to use --no-as-needed on
Linux.
Probable solutions:
Linux-specific solution:
libomp_append(libflags_local "-Wl,--as-needed" LIBOMP_HAVE_AS_NEEDED_FLAG)
- elseif(${CMAKE_SYSTEM_NAME} MATCHES "NetBSD")
+ elseif(${CMAKE_SYSTEM_NAME} MATCHES "Linux|NetBSD")
libomp_append(libflags_local -lm)
More generic solution:
libomp_append(libflags_local "-Wl,--as-needed" LIBOMP_HAVE_AS_NEEDED_FLAG)
- elseif(${CMAKE_SYSTEM_NAME} MATCHES "NetBSD")
+ else()
libomp_append(libflags_local -lm)</pre>
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