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Windows Override

Dynamically overriding on mimalloc on Windows 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 well:

  1. Use the C-runtime library as a DLL (using the /MD or /MDd switch).

  2. Link your program explicitly with the mimalloc.lib export library for the mimalloc.dll -- which contains all mimalloc functionality. To ensure the mimalloc.dll is actually loaded at run-time it is easiest to insert some call to the mimalloc API in the main function, like mi_version() (or use the /include:mi_version switch on the linker, or similarly, #pragma comment(linker, "/include:mi_version") in some source file). See the mimalloc-test-override project for an example on how to use this.

  3. The mimalloc-redirect.dll must be put in the same folder as the main mimalloc.dll 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 mimalloc.dll).

  4. Ensure the mimalloc.dll comes as early as possible in the import list of the final executable (so it can intercept all potential allocations). You can use minject -l <exe> to check this if needed.

For best performance on Windows with C++, it is also recommended to also override the new/delete operations (by including mimalloc-new-delete.h a single(!) source file in your project).

The environment variable MIMALLOC_DISABLE_REDIRECT=1 can be used to disable dynamic overriding at run-time. Use MIMALLOC_VERBOSE=1 to check if mimalloc was successfully redirected.

Other Platforms

You always link with mimalloc.dll but for different platforms you may need a specific redirection DLL:

  • x64: mimalloc-redirect.dll.
  • x86: mimalloc-redirect32.dll. Use for older 32-bit Windows programs.
  • arm64: mimalloc-redirect-arm64.dll. Use for native Windows arm64 programs.
  • arm64ec: mimalloc-redirect-arm64ec.dll. The arm64ec ABI is "emulation compatible" mode on Windows arm64. Unfortunately we cannot run x64 code emulated on Windows arm64 with the x64 mimalloc override directly (since the C runtime always uses arm64ec). Instead:
    1. Build the program as normal for x64 and link as normal with the x64 mimalloc.lib export library.
    2. Now separately build mimalloc.dll in arm64ec mode and overwrite your previous (x64) mimalloc.dll -- the loader can handle the mix of arm64ec and x64 code. Now use mimalloc-redirect-arm64ec.dll to match your new arm64ec mimalloc.dll. The main program stays as is and can be fully x64 or contain more arm64ec modules. At runtime, the arm64ec mimalloc.dll will run with native arm64 instructions while the rest of the program runs emulated x64.

Minject

We cannot always re-link an executable with mimalloc.dll, and similarly, we cannot always ensure that 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 (ucrtbase.dll) -- just put the mimalloc.dll into the import table (and put mimalloc-redirect.dll in the same directory) Such patching can be done for example with CFF Explorer.

The minject program can also do this from the command line Use minject --help for options:

> minject --help

minject:
  Injects the mimalloc dll into the import table of a 64-bit executable,
  and/or ensures that it comes first in het import table.

usage:
  > minject [options] <exe>

options:
  -h   --help        show this help
  -v   --verbose     be verbose
  -l   --list        only list imported modules
  -i   --inplace     update the exe in-place (make sure there is a backup!)
  -f   --force       always overwrite without prompting
       --postfix=<p> use <p> as a postfix to the mimalloc dll.
                     e.g. use --postfix=debug to link with mimalloc-debug.dll

notes:
  Without '--inplace' an injected <exe> is generated with the same name ending in '-mi'.
  Ensure 'mimalloc-redirect.dll' is in the same folder as the mimalloc dll.

examples:
  > minject --list myprogram.exe
  > minject --force --inplace myprogram.exe

For x86 32-bit binaries, use minject32, and for arm64 binaries use minject-arm64.