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* Added a "contents"-like list of questions at the beginning of the file
* Use stylsheets. Really, people, work with me here. * Stop using those silly <dl> and <dt> and whatever else tags * Close tags llvm-svn: 9760
This commit is contained in:
Misha Brukman
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docs/FAQ.html
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docs/FAQ.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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"http://www.w3.org/TR/html4/strict.dtd">
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<html>
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<head>
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<title>LLVM: Frequently Asked Questions</title>
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<style>
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@import url("llvm.css");
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.question { font-weight: bold }
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.answer { margin-left: 2em }
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</style>
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</head>
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<body>
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|
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<h1>
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<center>
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<div class="doc_title">
|
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LLVM: Frequently Asked Questions
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</center>
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</h1>
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</div>
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|
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<hr>
|
||||
|
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<!--=====================================================================-->
|
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<h2>
|
||||
<a name="license">Licenses</a>
|
||||
</h2>
|
||||
<!--=====================================================================-->
|
||||
|
||||
<dl compact>
|
||||
<dt> <b>Why are the LLVM source code and the front-end distributed
|
||||
under different licenses?</b>
|
||||
<dd>
|
||||
The C/C++ front-ends are based on GCC and must be distributed under
|
||||
the GPL. Our aim is to distribute LLVM source code under a <em>much
|
||||
less restrictive</em> license, in particular one that does not
|
||||
compel users who distribute tools based on modifying the source to
|
||||
redistribute the modified source code as well.
|
||||
<p>
|
||||
<dt><b>Does the University of Illinois Open Source License really qualify
|
||||
as an "open source" license?</b>
|
||||
<dd>Yes, the license is
|
||||
<a href="http://www.opensource.org/licenses/UoI-NCSA.php">certified</a>
|
||||
by the Open Source Initiative (OSI).
|
||||
<p>
|
||||
<dt> <b>Can I modify LLVM source code and redistribute the modified
|
||||
source?</b>
|
||||
<dd>
|
||||
Yes. The modified source distribution must retain the
|
||||
copyright notice and follow the three bulletted conditions listed in
|
||||
the <a href="http://llvm.cs.uiuc.edu/releases/1.0/LICENSE.TXT">LLVM license</a>.
|
||||
<p>
|
||||
<dt> <b>Can I modify LLVM source code and redistribute binaries or
|
||||
other tools based on it, without redistributing the source?</b>
|
||||
<dd>
|
||||
Yes, this is why we distribute LLVM under a less restrictive license
|
||||
than GPL, as explained in the first question above.
|
||||
<p>
|
||||
</dl>
|
||||
<hr>
|
||||
|
||||
<!--=====================================================================-->
|
||||
<h2>
|
||||
<a name="source">Source Code</a>
|
||||
</h2>
|
||||
<!--=====================================================================-->
|
||||
|
||||
<dl compact>
|
||||
<dt> <b>In what language is LLVM written?</b>
|
||||
<dd>
|
||||
All of the LLVM tools and libraries are written in C++ with extensive use
|
||||
of the STL.
|
||||
<p>
|
||||
|
||||
<dt><b>How portable is the LLVM source code?</b>
|
||||
<dd>
|
||||
The LLVM source code should be portable to most modern UNIX-like operating
|
||||
systems. Most of the code is written in standard C++ with operating
|
||||
system services abstracted to a support library. The tools required to
|
||||
build and test LLVM have been ported to a plethora of platforms.
|
||||
<p>
|
||||
Some porting problems may exist in the following areas:
|
||||
<ul>
|
||||
<li>The GCC front end code is not as portable as the LLVM suite, so it
|
||||
may not compile as well on unsupported platforms.
|
||||
|
||||
<p>
|
||||
|
||||
<li>The Python test classes are more UNIX-centric than they should be,
|
||||
so porting to non-UNIX like platforms (i.e. Windows, MacOS 9) will
|
||||
require some effort.
|
||||
<p>
|
||||
|
||||
<li>The LLVM build system relies heavily on UNIX shell tools, like the
|
||||
Bourne Shell and sed. Porting to systems without these tools (MacOS 9,
|
||||
Plan 9) will require more effort.
|
||||
</ul>
|
||||
</dl>
|
||||
|
||||
<hr>
|
||||
|
||||
<!--=====================================================================-->
|
||||
<h2>
|
||||
<a name="build">Build Problems</a>
|
||||
</h2>
|
||||
<!--=====================================================================-->
|
||||
|
||||
<dl compact>
|
||||
<dt><b>When I run configure, it finds the wrong C compiler.</b>
|
||||
<dd>
|
||||
The <tt>configure</tt> script attempts to locate first <tt>gcc</tt> and
|
||||
then <tt>cc</tt>, unless it finds compiler paths set in <tt>CC</tt> and
|
||||
<tt>CXX</tt> for the C and C++ compiler, respectively.
|
||||
|
||||
If <tt>configure</tt> finds the wrong compiler, either adjust your
|
||||
<tt>PATH</tt> environment variable or set <tt>CC</tt> and <tt>CXX</tt>
|
||||
explicitly.
|
||||
<p>
|
||||
|
||||
<dt><b>I compile the code, and I get some error about /localhome</b>.
|
||||
<dd>
|
||||
There are several possible causes for this. The first is that you
|
||||
didn't set a pathname properly when using <tt>configure</tt>, and it
|
||||
defaulted to a pathname that we use on our research machines.
|
||||
<p>
|
||||
Another possibility is that we hardcoded a path in our Makefiles. If
|
||||
you see this, please email the LLVM bug mailing list with the name of
|
||||
the offending Makefile and a description of what is wrong with it.
|
||||
|
||||
<dt><b>The <tt>configure</tt> script finds the right C compiler, but it
|
||||
uses the LLVM linker from a previous build. What do I do?</b>
|
||||
<dd>
|
||||
The <tt>configure</tt> script uses the <tt>PATH</tt> to find
|
||||
executables, so if it's grabbing the wrong linker/assembler/etc, there
|
||||
are two ways to fix it:
|
||||
<ol>
|
||||
<li>Adjust your <tt>PATH</tt> environment variable so that the
|
||||
correct program appears first in the <tt>PATH</tt>. This may work,
|
||||
but may not be convenient when you want them <i>first</i> in your
|
||||
path for other work.
|
||||
<p>
|
||||
<li><a href="#license">License</a>
|
||||
<ol>
|
||||
<li>Why are the LLVM source code and the front-end distributed under different
|
||||
licenses?</li>
|
||||
<li>Does the University of Illinois Open Source License really qualify as an
|
||||
"open source" license?</li>
|
||||
<li>Can I modify LLVM source code and redistribute the modified source?</li>
|
||||
<li>Can I modify LLVM source code and redistribute binaries or other tools
|
||||
based on it, without redistributing the source?</li>
|
||||
</ol></li>
|
||||
|
||||
<li>Run <tt>configure</tt> with an alternative <tt>PATH</tt> that
|
||||
is correct. In a Borne compatible shell, the syntax would be:
|
||||
<p>
|
||||
<tt>PATH=<the path without the bad program> ./configure ...</tt>
|
||||
<p>
|
||||
This is still somewhat inconvenient, but it allows
|
||||
<tt>configure</tt> to do its work without having to adjust your
|
||||
<tt>PATH</tt> permanently.
|
||||
<li><a href="#source">Source code</a>
|
||||
<ol>
|
||||
<li>In what language is LLVM written?</li>
|
||||
<li>How portable is the LLVM source code?</li>
|
||||
</ol></li>
|
||||
|
||||
<li><a href="#build">Build Problems</a>
|
||||
<ol>
|
||||
<li>When I run configure, it finds the wrong C compiler.</li>
|
||||
<li>I compile the code, and I get some error about <tt>/localhome</tt>.</li>
|
||||
<li>The <tt>configure</tt> script finds the right C compiler, but it uses the
|
||||
LLVM linker from a previous build. What do I do?</li>
|
||||
<li>When creating a dynamic library, I get a strange GLIBC error.</li>
|
||||
<li>I've updated my source tree from CVS, and now my build is trying to use a
|
||||
file/directory that doesn't exist.</li>
|
||||
<li>I've modified a Makefile in my source tree, but my build tree keeps using
|
||||
the old version. What do I do?</li>
|
||||
<li>I've upgraded to a new version of LLVM, and I get strange build
|
||||
errors.</li>
|
||||
<li>I've built LLVM and am testing it, but the tests freeze.</li>
|
||||
<li>Why do test results differ when I perform different types of builds?</li>
|
||||
</ol></li>
|
||||
</ol>
|
||||
|
||||
<dt><b>When creating a dynamic library, I get a strange GLIBC error.</b>
|
||||
<dd>
|
||||
Under some operating systems (i.e. Linux), libtool does not work correctly
|
||||
if GCC was compiled with the --disable-shared option. To work around this,
|
||||
install your own version of GCC that has shared libraries enabled by
|
||||
default.
|
||||
<p>
|
||||
<!-- *********************************************************************** -->
|
||||
<div class="doc_section">
|
||||
<a name="license">License</a>
|
||||
</div>
|
||||
<!-- *********************************************************************** -->
|
||||
|
||||
<dt><b>I've updated my source tree from CVS, and now my build is trying to
|
||||
use a file/directory that doesn't exist.</b>
|
||||
<dd>
|
||||
You need to re-run configure in your object directory. When new Makefiles
|
||||
are added to the source tree, they have to be copied over to the object
|
||||
tree in order to be used by the build.
|
||||
<p>
|
||||
<div class="question">
|
||||
<p>Why are the LLVM source code and the front-end distributed under different
|
||||
licenses?</p>
|
||||
</div>
|
||||
|
||||
<dt><b>I've modified a Makefile in my source tree, but my build tree keeps
|
||||
using the old version. What do I do?</b>
|
||||
<dd>
|
||||
If the Makefile already exists in your object tree, you can just run the
|
||||
following command in the top level directory of your object tree:
|
||||
<p>
|
||||
<tt>./config.status <relative path to Makefile></tt>
|
||||
<p>
|
||||
If the Makefile is new, you will have to modify the configure script to copy
|
||||
it over.
|
||||
<p>
|
||||
<div class="answer">
|
||||
<p>The C/C++ front-ends are based on GCC and must be distributed under the GPL.
|
||||
Our aim is to distribute LLVM source code under a <em>much less restrictive</em>
|
||||
license, in particular one that does not compel users who distribute tools based
|
||||
on modifying the source to redistribute the modified source code as well.</p>
|
||||
</div>
|
||||
|
||||
<dt><b>I've upgraded to a new version of LLVM, and I get strange build
|
||||
errors.</b>
|
||||
<dd>
|
||||
Sometimes changes to the LLVM source code alters how the build system
|
||||
works. Changes in libtool, autoconf, or header file dependencies are
|
||||
especially prone to this sort of problem.
|
||||
<p>
|
||||
The best thing to try is to remove the old files and re-build. In most
|
||||
<div class="question">
|
||||
<p>Does the University of Illinois Open Source License really qualify as an
|
||||
"open source" license?</p>
|
||||
</div>
|
||||
|
||||
<div class="answer">
|
||||
<p>Yes, the license is <a
|
||||
href="http://www.opensource.org/licenses/UoI-NCSA.php">certified</a> by the Open
|
||||
Source Initiative (OSI).</p>
|
||||
</div>
|
||||
|
||||
<div class="question">
|
||||
<p>Can I modify LLVM source code and redistribute the modified source?</p>
|
||||
</div>
|
||||
|
||||
<div class="answer">
|
||||
<p>Yes. The modified source distribution must retain the copyright notice and
|
||||
follow the three bulletted conditions listed in the <a
|
||||
href="http://llvm.cs.uiuc.edu/releases/1.0/LICENSE.TXT">LLVM license</a>.</p>
|
||||
</div>
|
||||
|
||||
<div class="question">
|
||||
<p>Can I modify LLVM source code and redistribute binaries or other tools based
|
||||
on it, without redistributing the source?</p>
|
||||
</div>
|
||||
|
||||
<div class="answer">
|
||||
<p>Yes, this is why we distribute LLVM under a less restrictive license than
|
||||
GPL, as explained in the first question above.</p>
|
||||
</div>
|
||||
|
||||
<!-- *********************************************************************** -->
|
||||
<div class="doc_section">
|
||||
<a name="source">Source Code</a>
|
||||
</div>
|
||||
<!-- *********************************************************************** -->
|
||||
|
||||
<div class="question">
|
||||
<p>In what language is LLVM written?</p>
|
||||
</div>
|
||||
|
||||
<div class="answer">
|
||||
<p>All of the LLVM tools and libraries are written in C++ with extensive use of
|
||||
the STL.</p>
|
||||
</div>
|
||||
|
||||
<div class="question">
|
||||
<p>How portable is the LLVM source code?</p>
|
||||
</div>
|
||||
|
||||
<div class="answer">
|
||||
<p>The LLVM source code should be portable to most modern UNIX-like operating
|
||||
systems. Most of the code is written in standard C++ with operating system
|
||||
services abstracted to a support library. The tools required to build and test
|
||||
LLVM have been ported to a plethora of platforms.</p>
|
||||
|
||||
<p>Some porting problems may exist in the following areas:</p>
|
||||
|
||||
<ul>
|
||||
|
||||
<li>The GCC front end code is not as portable as the LLVM suite, so it may not
|
||||
compile as well on unsupported platforms.</li>
|
||||
|
||||
<li>The Python test classes are more UNIX-centric than they should be, so
|
||||
porting to non-UNIX like platforms (i.e. Windows, MacOS 9) will require some
|
||||
effort.</li>
|
||||
|
||||
<li>The LLVM build system relies heavily on UNIX shell tools, like the Bourne
|
||||
Shell and sed. Porting to systems without these tools (MacOS 9, Plan 9) will
|
||||
require more effort.</li>
|
||||
|
||||
</ul>
|
||||
|
||||
</div>
|
||||
|
||||
<!-- *********************************************************************** -->
|
||||
<div class="doc_section">
|
||||
<a name="build">Build Problems</a>
|
||||
</div>
|
||||
<!-- *********************************************************************** -->
|
||||
|
||||
<div class="question">
|
||||
<p>When I run configure, it finds the wrong C compiler.</p>
|
||||
</div>
|
||||
|
||||
<div class="answer">
|
||||
|
||||
<p>The <tt>configure</tt> script attempts to locate first <tt>gcc</tt> and then
|
||||
<tt>cc</tt>, unless it finds compiler paths set in <tt>CC</tt> and <tt>CXX</tt>
|
||||
for the C and C++ compiler, respectively.</p>
|
||||
|
||||
<p>If <tt>configure</tt> finds the wrong compiler, either adjust your
|
||||
<tt>PATH</tt> environment variable or set <tt>CC</tt> and <tt>CXX</tt>
|
||||
explicitly.</p>
|
||||
|
||||
</div>
|
||||
|
||||
<div class="question">
|
||||
<p>I compile the code, and I get some error about <tt>/localhome</tt>.</p>
|
||||
</div>
|
||||
|
||||
<div class="answer">
|
||||
|
||||
<p>There are several possible causes for this. The first is that you didn't set
|
||||
a pathname properly when using <tt>configure</tt>, and it defaulted to a
|
||||
pathname that we use on our research machines.</p>
|
||||
|
||||
<p>Another possibility is that we hardcoded a path in our Makefiles. If you see
|
||||
this, please email the LLVM bug mailing list with the name of the offending
|
||||
Makefile and a description of what is wrong with it.</p>
|
||||
|
||||
</div>
|
||||
|
||||
<div class="question">
|
||||
<p>The <tt>configure</tt> script finds the right C compiler, but it uses the
|
||||
LLVM linker from a previous build. What do I do?</p>
|
||||
</div>
|
||||
|
||||
<div class="answer">
|
||||
<p>The <tt>configure</tt> script uses the <tt>PATH</tt> to find executables, so
|
||||
if it's grabbing the wrong linker/assembler/etc, there are two ways to fix
|
||||
it:</p>
|
||||
|
||||
<ol>
|
||||
|
||||
<li><p>Adjust your <tt>PATH</tt> environment variable so that the correct
|
||||
program appears first in the <tt>PATH</tt>. This may work, but may not be
|
||||
convenient when you want them <i>first</i> in your path for other
|
||||
work.</p></li>
|
||||
|
||||
<li><p>Run <tt>configure</tt> with an alternative <tt>PATH</tt> that is
|
||||
correct. In a Borne compatible shell, the syntax would be:</p>
|
||||
|
||||
<p><tt>PATH=<the path without the bad program> ./configure ...</tt></p>
|
||||
|
||||
<p>This is still somewhat inconvenient, but it allows <tt>configure</tt>
|
||||
to do its work without having to adjust your <tt>PATH</tt>
|
||||
permanently.</p></li>
|
||||
|
||||
</ol>
|
||||
|
||||
</div>
|
||||
|
||||
<div class="question">
|
||||
<p>When creating a dynamic library, I get a strange GLIBC error.</p>
|
||||
</div>
|
||||
|
||||
<div class="answer">
|
||||
<p>Under some operating systems (i.e. Linux), libtool does not work correctly if
|
||||
GCC was compiled with the --disable-shared option. To work around this, install
|
||||
your own version of GCC that has shared libraries enabled by default.</p>
|
||||
</div>
|
||||
|
||||
<div class="question">
|
||||
<p>I've updated my source tree from CVS, and now my build is trying to use a
|
||||
file/directory that doesn't exist.</p>
|
||||
</div>
|
||||
|
||||
<div class="answer">
|
||||
<p>You need to re-run configure in your object directory. When new Makefiles
|
||||
are added to the source tree, they have to be copied over to the object tree in
|
||||
order to be used by the build.</p>
|
||||
</div>
|
||||
|
||||
<div class="question">
|
||||
<p>I've modified a Makefile in my source tree, but my build tree keeps using the
|
||||
old version. What do I do?</p>
|
||||
</div>
|
||||
|
||||
<div class="answer">
|
||||
|
||||
<p>If the Makefile already exists in your object tree, you
|
||||
can just run the following command in the top level directory of your object
|
||||
tree:</p>
|
||||
|
||||
<p><tt>./config.status <relative path to Makefile></tt><p>
|
||||
|
||||
<p>If the Makefile is new, you will have to modify the configure script to copy
|
||||
it over.</p>
|
||||
|
||||
</div>
|
||||
|
||||
<div class="question">
|
||||
<p>I've upgraded to a new version of LLVM, and I get strange build errors.</p>
|
||||
</div>
|
||||
|
||||
<div class="answer">
|
||||
|
||||
<p>Sometimes, changes to the LLVM source code alters how the build system works.
|
||||
Changes in libtool, autoconf, or header file dependencies are especially prone
|
||||
to this sort of problem.</p>
|
||||
|
||||
<p>The best thing to try is to remove the old files and re-build. In most
|
||||
cases, this takes care of the problem. To do this, just type <tt>make
|
||||
clean</tt> and then <tt>make</tt> in the directory that fails to build.
|
||||
<p>
|
||||
clean</tt> and then <tt>make</tt> in the directory that fails to build.</p>
|
||||
|
||||
<dt><b>I've built LLVM and am testing it, but the tests freeze.</b>
|
||||
<dd>
|
||||
This is most likely occurring because you built a profile or release
|
||||
(optimized) build of LLVM and have not specified the same information on
|
||||
the <tt>gmake</tt> command line.
|
||||
<p>
|
||||
For example, if you built LLVM with the command:
|
||||
<p>
|
||||
<tt>gmake ENABLE_PROFILING=1</tt>
|
||||
<p>
|
||||
...then you must run the tests with the following commands:
|
||||
<p>
|
||||
<tt>cd llvm/test<br>gmake ENABLE_PROFILING=1</tt>
|
||||
<p>
|
||||
</div>
|
||||
|
||||
<div class="question">
|
||||
<p>I've built LLVM and am testing it, but the tests freeze.</p>
|
||||
</div>
|
||||
|
||||
<div class="answer">
|
||||
|
||||
<p>This is most likely occurring because you built a profile or release
|
||||
(optimized) build of LLVM and have not specified the same information on the
|
||||
<tt>gmake</tt> command line.</p>
|
||||
|
||||
<p>For example, if you built LLVM with the command:</p>
|
||||
|
||||
<p><tt>gmake ENABLE_PROFILING=1</tt>
|
||||
|
||||
<p>...then you must run the tests with the following commands:</p>
|
||||
|
||||
<p><tt>cd llvm/test<br>gmake ENABLE_PROFILING=1</tt></p>
|
||||
|
||||
</div>
|
||||
|
||||
<div class="question">
|
||||
<p>Why do test results differ when I perform different types of builds?</p>
|
||||
</div>
|
||||
|
||||
<div class="answer">
|
||||
|
||||
<p>The LLVM test suite is dependent upon several features of the LLVM tools and
|
||||
libraries.</p>
|
||||
|
||||
<p>First, the debugging assertions in code are not enabled in optimized or
|
||||
profiling builds. Hence, tests that used to fail may pass.</p>
|
||||
|
||||
<p>Second, some tests may rely upon debugging options or behavior that is only
|
||||
available in the debug build. These tests will fail in an optimized or profile
|
||||
build.</p>
|
||||
|
||||
</div>
|
||||
|
||||
<!-- *********************************************************************** -->
|
||||
|
||||
<dt><b>Why do test results differ when I perform different types of
|
||||
builds?</b>
|
||||
<dd>
|
||||
The LLVM test suite is dependent upon several features of the LLVM tools
|
||||
and libraries.
|
||||
<p>
|
||||
First, the debugging assertions in code are not enabled in optimized or
|
||||
profiling builds. Hence, tests that used to fail may pass.
|
||||
<p>
|
||||
Second, some tests may rely upon debugging options or behavior that is
|
||||
only available in the debug build. These tests will fail in an optimized
|
||||
or profile build.
|
||||
</dl>
|
||||
<hr>
|
||||
|
||||
<div class="doc_footer">
|
||||
<a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a>
|
||||
<br>
|
||||
Last modified: $Date$
|
||||
</div>
|
||||
|
||||
</body>
|
||||
</html>
|
||||
|
||||
Loading…
Reference in New Issue
Block a user