docs/4.0-migration-guide/repo-split.md

## CMake as the only build system
Mbed TLS now uses CMake exclusively to configure and drive its build process.
Support for the GNU Make and Microsoft Visual Studio project-based build systems has been removed.

The previous `.sln` and `.vcxproj` files are no longer distributed or generated.

See the `Compiling` section in README.md for instructions on building the Mbed TLS libraries and tests with CMake.
If you develop in Microsoft Visual Studio, you could either generate a Visual Studio solution using a CMake generator, or open the CMake project directly in Visual Studio.

### Translating Make commands to CMake

With the removal of GNU Make support, all build, test, and installation operations must now be performed using CMake.
This section provides a quick reference for translating common `make` commands into their CMake equivalents.

#### Basic build workflow

Run `cmake -S . -B build` once before building to configure the build and generate native build files (e.g., Makefiles) in the `build` directory.
This sets up an out-of-tree build, which is recommended.

| Make command   | CMake equivalent                               | Description                                                        |
|----------------|------------------------------------------------|--------------------------------------------------------------------|
| `make`         | `cmake --build build`                          | Build the libraries, programs, and tests in the `build` directory. |
| `make test`    | `ctest --test-dir build`                       | Run the tests produced by the previous build. |
| `make clean`   | `cmake --build build --target clean`           | Remove build artifacts produced by the previous build. |
| `make install` | `cmake --install build --prefix build/install` | Install the built libraries, headers, and tests to `build/install`. |

#### Building specific targets

Unless otherwise specified, the CMake command in the table below should be preceded by a `cmake -S . -B build` call to configure the build and generate build files in the `build` directory.

| Make command    | CMake equivalent                                                    | Description               |
|-----------------|---------------------------------------------------------------------|---------------------------|
| `make lib`      | `cmake --build build --target lib`                                  | Build only the libraries. |
| `make tests`    | `cmake -S . -B build -DENABLE_PROGRAMS=Off && cmake --build build`  | Build test suites. |
| `make programs` | `cmake --build build --target programs`                             | Build example programs. |
| `make apidoc`   | `cmake --build build --target mbedtls-apidoc`                       | Build documentation. |

Target names may differ slightly; use `cmake --build build --target help` to list all available CMake targets.

There is no CMake equivalent for `make generated_files` or `make neat`.
Generated files are automatically created in the build tree with `cmake --build build` and removed with `cmake --build build --target clean`.
If you need to build the generated files in the source tree without involving CMake, you can call `framework/scripts/make_generated_files.py`.

There is no CMake equivalent for `make uninstall`.
To remove an installation, simply delete the directory specified as the installation prefix.

#### Common build options

| Make usage                 | CMake usage                                           | Description          |
|----------------------------|-------------------------------------------------------|----------------------|
| `make DEBUG=1`             | `cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug`        | Build in debug mode. |
| `make SHARED=1`            | `cmake -S . -B build -DUSE_SHARED_MBEDTLS_LIBRARY=On` | Also build shared libraries. |
| `make GEN_FILES=""`        | `cmake -S . -B build -DGEN_FILES=OFF`                 | Skip generating files (not a strict equivalent). |
| `make DESTDIR=install_dir` | `cmake --install build --prefix install_dir`          | Specify installation path. |
| `make CC=clang`            | `cmake -S . -B build -DCMAKE_C_COMPILER=clang`        | Set the compiler. |
| `make CFLAGS='-O2 -Wall'`  | `cmake -S . -B build -DCMAKE_C_FLAGS="-O2 -Wall"`     | Set compiler flags. |

## Repository split
In Mbed TLS 4.0, the project was split into two repositories:
- [Mbed TLS](https://github.com/Mbed-TLS/mbedtls): provides TLS and X.509 functionality.
- [TF-PSA-Crypto](https://github.com/Mbed-TLS/TF-PSA-Crypto): provides the standalone cryptography library, implementing the PSA Cryptography API.
Mbed TLS consumes TF-PSA-Crypto as a submodule.
You should stay with Mbed TLS if you use TLS or X.509 functionality. You still have direct access to the cryptography library.

### File and directory relocations

The following table summarizes the file and directory relocations resulting from the repository split between Mbed TLS and TF-PSA-Crypto.
These changes reflect the move of cryptographic, cryptographic-adjacent, and platform components from Mbed TLS into the new TF-PSA-Crypto repository.

| Original location                       | New location(s)                                                                      | Notes |
|-----------------------------------------|--------------------------------------------------------------------------------------|-------|
| `library/*`  (\*)                       | `tf-psa-crypto/core/`<br>`tf-psa-crypto/drivers/builtin/src/`                        | Contains cryptographic, cryptographic-adjacent (e.g., ASN.1, Base64), and platform C modules and headers. |
| `include/mbedtls/*`  (\*)               | `tf-psa-crypto/include/mbedtls/`<br>`tf-psa-crypto/drivers/builtin/include/private/` | Public headers moved to `include/mbedtls`; now internal headers moved to `include/private`. |
| `include/psa`                           | `tf-psa-crypto/include/psa`                                                          | All PSA headers consolidated here. |
| `3rdparty/everest`<br>`3rdparty/p256-m` | `tf-psa-crypto/drivers/everest`<br>`tf-psa-crypto/drivers/p256-m`                    | Third-party crypto driver implementations. |

(\*) The `library` and `include/mbedtls` directories still exist in Mbed TLS, but not contain only TLS and X.509 components.

### Configuration file split
Cryptography and platform configuration options have been moved from `include/mbedtls/mbedtls_config.h` to `tf-psa-crypto/include/psa/crypto_config.h`, which is now mandatory.
See [Compile-time configuration](#compile-time-configuration).

The header `include/mbedtls/mbedtls_config.h` still exists and now contains only the TLS and X.509 configuration options.

If you use the Python script `scripts/config.py` to adjust your configuration, you do not need to modify your scripts to specify which configuration file to edit, the script automatically updates the correct file.

There has been significant changes in the configuration options, primarily affecting cryptography.

#### Cryptography configuration
- See [psa-transition.md](https://github.com/Mbed-TLS/TF-PSA-Crypto/blob/development/docs/psa-transition.md#compile-time-configuration).
- See also the following sections in the TF-PSA-Crypto 1.0 migration guide:
  - *PSA as the Only Cryptography API* and its sub-section *Impact on the Library Configuration*
  - *Random Number Generation Configuration*

#### TLS configuration
For details about TLS-related changes, see [Changes to TLS options](#changes-to-tls-options).

### Impact on some usages of the library

#### Checking out a branch or a tag
After checking out a branch or tag of the Mbed TLS repository, you must now recursively update the submodules, as TF-PSA-Crypto contains itself a nested submodule:
```
git submodule update --init --recursive
```

#### Linking directly to a built library
The Mbed TLS CMake build system still provides the cryptography libraries under their legacy name, `libmbedcrypto.<ext>`, so you can continue linking against them.
The cryptography libraries are also now provided as `libtfpsacrypto.<ext>` like in the TF-PSA-Crypto repository.

#### Linking through a CMake target of the cryptography library
The base name of the CMake cryptography library target has been changed from `mbedcrypto` to `tfpsacrypto`.
If no target prefix is specified through the MBEDTLS_TARGET_PREFIX option, the associated CMake target is thus now `tfpsacrypto`.

The same renaming applies to the cryptography library targets declared as part of the Mbed TLS CMake package.
When no global target prefix is defined, use `MbedTLS::tfpsacrypto` instead of `MbedTLS::mbedcrypto`.

As an example, the following CMake code:
```
find_package(MbedTLS REQUIRED)
target_link_libraries(myapp PRIVATE MbedTLS::mbedtls MbedTLS::mbedx509 MbedTLS::mbedcrypto)

```
would be updated to something like
```
find_package(MbedTLS REQUIRED)
target_link_libraries(myapp PRIVATE MbedTLS::mbedtls MbedTLS::mbedx509 MbedTLS::tfpsacrypto)
```

For more information, see the CMake section of `README.md`.
You can also refer to the following example programs demonstrating how to consume Mbed TLS via CMake:
* `programs/test/cmake_subproject`
* `programs/test/cmake_package`
* `programs/test/cmake_package_install`.

#### Using Mbed TLS Crypto pkg-config file
The Mbed TLS CMake build system still provides the pkg-config file mbedcrypto.pc, so you can continue using it. Internally, it now references the `tfpsacrypto` library.
A new pkg-config file, `tfpsacrypto.pc`, is also provided.
Both `mbedcrypto.pc` and `tfpsacrypto.pc` are functionally equivalent, providing the same compiler and linker flags.

### Audience-Specific Notes

#### Application Developers using a distribution package
- See [Impact on usages of the library](#impact-on-some-usages-of-the-library) for the possible impacts on:
  - Linking against the cryptography library or CMake targets.
  - Use the updated `pkg-config` files (`mbedcrypto.pc` / `tfpsacrypto.pc`).

### Developer or package maintainers
If you build or distribute Mbed TLS:
- The build system is now CMake only, Makefiles and Visual Studio projects are removed.
- You may need to adapt packaging scripts to handle the TF-PSA-Crypto submodule.
- You should update submodules recursively after checkout.
- Review [File and directory relocations](#file-and-directory-relocations) for updated paths.
- See [Impact on usages of the library](#impact-on-some-usages-of-the-library) for the possible impacts on:
  - Linking against the cryptography library or CMake targets.
  - Use the updated `pkg-config` files (`mbedcrypto.pc` / `tfpsacrypto.pc`).
- Configuration note: cryptography and platform options are now in `crypto_config.h` (see [Configuration file split](#configuration-file-split)).

### Platform Integrators
If you integrate Mbed TLS with a platform or hardware drivers:
- TF-PSA-Crypto is now a submodule, update integration scripts to initialize submodules recursively.
- The PSA driver wrapper is now generated in TF-PSA-Crypto.
- Platform-specific configuration are now handled in `crypto_config.h`.
- See [Repository split](#repository-split) for how platform components moved to TF-PSA-Crypto.