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<div class="title">Overriding Malloc </div>  </div>
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<div class="textblock"><p>Overriding the standard <code>malloc</code> can be done either <em>dynamically</em> or <em>statically</em>.</p>
<h2>Dynamic override</h2>
<p>This is the recommended way to override the standard malloc interface.</p>
<h3>Linux, BSD</h3>
<p>On these systems we preload the mimalloc shared library so all calls to the standard <code>malloc</code> interface are resolved to the <em>mimalloc</em> library.</p>
<ul>
<li><code>env LD_PRELOAD=/usr/lib/libmimalloc.so myprogram</code></li>
</ul>
<p>You can set extra environment variables to check that mimalloc is running, like: </p><div class="fragment"><div class="line">env MIMALLOC_VERBOSE=1 LD_PRELOAD=/usr/lib/libmimalloc.so myprogram</div></div><!-- fragment --><p> or run with the debug version to get detailed statistics: </p><div class="fragment"><div class="line">env MIMALLOC_SHOW_STATS=1 LD_PRELOAD=/usr/lib/libmimalloc-debug.so myprogram</div></div><!-- fragment --><h3>MacOS</h3>
<p>On macOS we can also preload the mimalloc shared library so all calls to the standard <code>malloc</code> interface are resolved to the <em>mimalloc</em> library.</p>
<ul>
<li><code>env DYLD_FORCE_FLAT_NAMESPACE=1 DYLD_INSERT_LIBRARIES=/usr/lib/libmimalloc.dylib myprogram</code></li>
</ul>
<p>Note that certain security restrictions may apply when doing this from the <a href="https://stackoverflow.com/questions/43941322/dyld-insert-libraries-ignored-when-calling-application-through-bash">shell</a>.</p>
<p>Note: unfortunately, at this time, dynamic overriding on macOS seems broken but it is actively worked on to fix this (see issue <a href="https://github.com/microsoft/mimalloc/issues/50"><code>#50</code></a>).</p>
<h3>Windows</h3>
<p>Overriding on Windows is robust but requires that you link your program explicitly with the mimalloc DLL and use the C-runtime library as a DLL (using the <code>/MD</code> or <code>/MDd</code> switch). Moreover, you need to ensure the <code>mimalloc-redirect.dll</code> (or <code>mimalloc-redirect32.dll</code>) is available in the same folder as the main <code>mimalloc-override.dll</code> at runtime (as it is a dependency). The redirection DLL ensures that all calls to the C runtime malloc API get redirected to mimalloc (in <code>mimalloc-override.dll</code>).</p>
<p>To ensure the mimalloc DLL is loaded at run-time it is easiest to insert some call to the mimalloc API in the <code>main</code> function, like <code>mi_version()</code> (or use the <code>/INCLUDE:mi_version</code> switch on the linker). See the <code>mimalloc-override-test</code> project for an example on how to use this. For best performance on Windows with C++, it is highly recommended to also override the <code>new</code>/<code>delete</code> operations (by including <a href="https://github.com/microsoft/mimalloc/blob/master/include/mimalloc-new-delete.h"><code>mimalloc-new-delete.h</code></a> a single(!) source file in your project).</p>
<p>The environment variable <code>MIMALLOC_DISABLE_REDIRECT=1</code> can be used to disable dynamic overriding at run-time. Use <code>MIMALLOC_VERBOSE=1</code> to check if mimalloc was successfully redirected.</p>
<p>(Note: in principle, it is possible to patch existing executables that are linked with the dynamic C runtime (<code>ucrtbase.dll</code>) by just putting the <code>mimalloc-override.dll</code> into the import table (and putting <code>mimalloc-redirect.dll</code> in the same folder) Such patching can be done for example with <a href="https://ntcore.com/?page_id=388">CFF Explorer</a>).</p>
<h2>Static override</h2>
<p>On Unix systems, you can also statically link with <em>mimalloc</em> to override the standard malloc interface. The recommended way is to link the final program with the <em>mimalloc</em> single object file (<code>mimalloc-override.o</code>). We use an object file instead of a library file as linkers give preference to that over archives to resolve symbols. To ensure that the standard malloc interface resolves to the <em>mimalloc</em> library, link it as the first object file. For example:</p>
<div class="fragment"><div class="line">gcc -o myprogram mimalloc-<span class="keyword">override</span>.o  myfile1.c ...</div></div><!-- fragment --><h2>List of Overrides:</h2>
<p>The specific functions that get redirected to the <em>mimalloc</em> library are:</p>
<div class="fragment"><div class="line"><span class="comment">// C</span></div><div class="line"><span class="keywordtype">void</span>*  malloc(<span class="keywordtype">size_t</span> size);</div><div class="line"><span class="keywordtype">void</span>*  calloc(<span class="keywordtype">size_t</span> size, <span class="keywordtype">size_t</span> n);</div><div class="line"><span class="keywordtype">void</span>*  realloc(<span class="keywordtype">void</span>* p, <span class="keywordtype">size_t</span> newsize);</div><div class="line"><span class="keywordtype">void</span>   free(<span class="keywordtype">void</span>* p);</div><div class="line"></div><div class="line"><span class="comment">// C++</span></div><div class="line"><span class="keywordtype">void</span>   <span class="keyword">operator</span> <span class="keyword">delete</span>(<span class="keywordtype">void</span>* p);</div><div class="line"><span class="keywordtype">void</span>   <span class="keyword">operator</span> <span class="keyword">delete</span>[](<span class="keywordtype">void</span>* p);</div><div class="line"></div><div class="line"><span class="keywordtype">void</span>*  <span class="keyword">operator</span> <span class="keyword">new</span>(std::size_t n) noexcept(<span class="keyword">false</span>);</div><div class="line"><span class="keywordtype">void</span>*  <span class="keyword">operator</span> <span class="keyword">new</span>[](std::size_t n) noexcept(<span class="keyword">false</span>);</div><div class="line"><span class="keywordtype">void</span>*  <span class="keyword">operator</span> <span class="keyword">new</span>( std::size_t n, std::align_val_t align) noexcept(<span class="keyword">false</span>);</div><div class="line"><span class="keywordtype">void</span>*  <span class="keyword">operator</span> <span class="keyword">new</span>[]( std::size_t n, std::align_val_t align) noexcept(<span class="keyword">false</span>);</div><div class="line"></div><div class="line"><span class="keywordtype">void</span>*  <span class="keyword">operator</span> <span class="keyword">new</span>  ( std::size_t count, <span class="keyword">const</span> std::nothrow_t&amp; tag);</div><div class="line"><span class="keywordtype">void</span>*  <span class="keyword">operator</span> <span class="keyword">new</span>[]( std::size_t count, <span class="keyword">const</span> std::nothrow_t&amp; tag);</div><div class="line"><span class="keywordtype">void</span>*  <span class="keyword">operator</span> <span class="keyword">new</span>  ( std::size_t count, std::align_val_t al, <span class="keyword">const</span> std::nothrow_t&amp;);</div><div class="line"><span class="keywordtype">void</span>*  <span class="keyword">operator</span> <span class="keyword">new</span>[]( std::size_t count, std::align_val_t al, <span class="keyword">const</span> std::nothrow_t&amp;);</div><div class="line"></div><div class="line"><span class="comment">// Posix</span></div><div class="line"><span class="keywordtype">int</span>    posix_memalign(<span class="keywordtype">void</span>** p, <span class="keywordtype">size_t</span> alignment, <span class="keywordtype">size_t</span> size);</div><div class="line"></div><div class="line"><span class="comment">// Linux</span></div><div class="line"><span class="keywordtype">void</span>*  memalign(<span class="keywordtype">size_t</span> alignment, <span class="keywordtype">size_t</span> size);</div><div class="line"><span class="keywordtype">void</span>*  aligned_alloc(<span class="keywordtype">size_t</span> alignment, <span class="keywordtype">size_t</span> size);</div><div class="line"><span class="keywordtype">void</span>*  valloc(<span class="keywordtype">size_t</span> size);</div><div class="line"><span class="keywordtype">void</span>*  pvalloc(<span class="keywordtype">size_t</span> size);</div><div class="line"><span class="keywordtype">size_t</span> malloc_usable_size(<span class="keywordtype">void</span> *p);</div><div class="line"></div><div class="line"><span class="comment">// BSD</span></div><div class="line"><span class="keywordtype">void</span>*  reallocarray( <span class="keywordtype">void</span>* p, <span class="keywordtype">size_t</span> count, <span class="keywordtype">size_t</span> size );</div><div class="line"><span class="keywordtype">void</span>*  reallocf(<span class="keywordtype">void</span>* p, <span class="keywordtype">size_t</span> newsize);</div><div class="line"><span class="keywordtype">void</span>   cfree(<span class="keywordtype">void</span>* p);</div><div class="line"></div><div class="line"><span class="comment">// Windows</span></div><div class="line"><span class="keywordtype">void</span>*  _expand(<span class="keywordtype">void</span>* p, <span class="keywordtype">size_t</span> newsize);</div><div class="line"><span class="keywordtype">size_t</span> _msize(<span class="keywordtype">void</span>* p);</div><div class="line"></div><div class="line"><span class="keywordtype">void</span>*  _malloc_dbg(<span class="keywordtype">size_t</span> size, <span class="keywordtype">int</span> block_type, <span class="keyword">const</span> <span class="keywordtype">char</span>* fname, <span class="keywordtype">int</span> line);</div><div class="line"><span class="keywordtype">void</span>*  _realloc_dbg(<span class="keywordtype">void</span>* p, <span class="keywordtype">size_t</span> newsize, <span class="keywordtype">int</span> block_type, <span class="keyword">const</span> <span class="keywordtype">char</span>* fname, <span class="keywordtype">int</span> line);</div><div class="line"><span class="keywordtype">void</span>*  _calloc_dbg(<span class="keywordtype">size_t</span> count, <span class="keywordtype">size_t</span> size, <span class="keywordtype">int</span> block_type, <span class="keyword">const</span> <span class="keywordtype">char</span>* fname, <span class="keywordtype">int</span> line);</div><div class="line"><span class="keywordtype">void</span>*  _expand_dbg(<span class="keywordtype">void</span>* p, <span class="keywordtype">size_t</span> size, <span class="keywordtype">int</span> block_type, <span class="keyword">const</span> <span class="keywordtype">char</span>* fname, <span class="keywordtype">int</span> line);</div><div class="line"><span class="keywordtype">size_t</span> _msize_dbg(<span class="keywordtype">void</span>* p, <span class="keywordtype">int</span> block_type);</div><div class="line"><span class="keywordtype">void</span>   _free_dbg(<span class="keywordtype">void</span>* p, <span class="keywordtype">int</span> block_type);</div></div><!-- fragment --> </div></div><!-- PageDoc -->
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