<divclass="textblock"><p>Overriding the standard <code>malloc</code> (and <code>new</code>) can be done either <em>dynamically</em> or <em>statically</em>.</p>
<p>On these ELF-based 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><divclass="fragment"><divclass="line">> env LD_PRELOAD=/usr/lib/libmimalloc.so myprogram</div>
</div><!-- fragment --><p>You can set extra environment variables to check that mimalloc is running, like: </p><divclass="fragment"><divclass="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><divclass="fragment"><divclass="line">> env MIMALLOC_SHOW_STATS=1 LD_PRELOAD=/usr/lib/libmimalloc-debug.so myprogram</div>
</div><!-- fragment --><h3>Dynamic Override on 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><divclass="fragment"><divclass="line">> env DYLD_INSERT_LIBRARIES=/usr/lib/libmimalloc.dylib myprogram</div>
</div><!-- fragment --><p>Note that certain security restrictions may apply when doing this from the <ahref="https://stackoverflow.com/questions/43941322/dyld-insert-libraries-ignored-when-calling-application-through-bash">shell</a>.</p>
<h3>Dynamic Override on Windows</h3>
<p><spanid="override_on_windows">Dynamically overriding on mimalloc on Windows</span> is robust and has the particular advantage to be able to redirect all malloc/free calls that go through the (dynamic) C runtime allocator, including those from other DLL's or libraries. As it intercepts all allocation calls on a low level, it can be used reliably on large programs that include other 3rd party components. There are four requirements to make the overriding work robustly:</p>
<oltype="1">
<li>Use the C-runtime library as a DLL (using the <code>/MD</code> or <code>/MDd</code> switch).</li>
<li>Link your program explicitly with <code>mimalloc-override.dll</code> library. To ensure the <code>mimalloc-override.dll</code> 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.</li>
<li>The [<code>mimalloc-redirect.dll</code>](bin) (or <code>mimalloc-redirect32.dll</code>) must be put in the same folder as the main <code>mimalloc-override.dll</code> at runtime (as it is a dependency of that DLL). The redirection DLL ensures that all calls to the C runtime malloc API get redirected to mimalloc functions (which reside in <code>mimalloc-override.dll</code>).</li>
<li>Ensure the <code>mimalloc-override.dll</code> comes as early as possible in the import list of the final executable (so it can intercept all potential allocations).</li>
</ol>
<p>For best performance on Windows with C++, it is also recommended to also override the <code>new</code>/<code>delete</code> operations (by including <ahref="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>We cannot always re-link an executable with <code>mimalloc-override.dll</code>, and similarly, we cannot always ensure the the DLL comes first in the import table of the final executable. In many cases though we can patch existing executables without any recompilation if they are linked with the dynamic C runtime (<code>ucrtbase.dll</code>) – just put the <code>mimalloc-override.dll</code> into the import table (and put <code>mimalloc-redirect.dll</code> in the same folder) Such patching can be done for example with <ahref="https://ntcore.com/?page_id=388">CFF Explorer</a> or the [<code>minject</code>](bin) program.</p>
<p>On Unix-like 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.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><divclass="fragment"><divclass="line">> gcc -o myprogram mimalloc.o myfile1.c ...</div>
</div><!-- fragment --><p>Another way to override statically that works on all platforms, is to link statically to mimalloc (as shown in the introduction) and include a header file in each source file that re-defines <code>malloc</code> etc. to <code>mi_malloc</code>. This is provided by <ahref="https://github.com/microsoft/mimalloc/blob/master/include/mimalloc-override.h"><code>mimalloc-override.h</code></a>. This only works reliably though if all sources are under your control or otherwise mixing of pointers from different heaps may occur!</p>
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