3.3 KiB
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:
-
Use the C-runtime library as a DLL (using the
/MD
or/MDd
switch). -
Link your program explicitly with
mimalloc-override.dll
library. To ensure themimalloc-override.dll
is loaded at run-time it is easiest to insert some call to the mimalloc API in themain
function, likemi_version()
(or use the/INCLUDE:mi_version
switch on the linker). See themimalloc-override-test
project for an example on how to use this. -
The
mimalloc-redirect.dll
(ormimalloc-redirect32.dll
) must be put in the same folder as the mainmimalloc-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 inmimalloc-override.dll
). -
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