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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 robustly:

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

  2. Link your program explicitly with mimalloc-override.dll library. To ensure the mimalloc-override.dll is 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). See the mimalloc-override-test project for an example on how to use this.

  3. The mimalloc-redirect.dll (or mimalloc-redirect32.dll) must be put in the same folder as the main mimalloc-override.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-override.dll).

  4. Ensure the mimalloc-override.dll comes as early as possible in the import list of the final executable (so it can intercept all potential allocations).

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.

Minject

We cannot always re-link an executable with mimalloc-override.dll, 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 (ucrtbase.dll) -- just put the mimalloc-override.dll into the import table (and put mimalloc-redirect.dll in the same folder) 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 (default is 'override')
                     e.g. use --postfix=override-debug to link with mimalloc-override-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