Failed compilation on Cygwin

[Aethedor]

Summary

Version 4.0.0 doesn't compile on Cygwin.

System information

Using the latest Cygwin on a Windows machine.
mbedTLS version 4.0.0

Expected behavior

A successful compilation.

Actual behavior

Several CMake errors.

=== Python warning

CMake Warning (dev) at /usr/share/cmake-4.2.1/Modules/FindPython/Support.cmake:2088 (find_program):
  Policy CMP0109 is not set: find_program() requires permission to execute
  but not to read.  Run "cmake --help-policy CMP0109" for policy details.
  Use the cmake_policy command to set the policy and suppress this warning.

  The file

    /cygdrive/c/Users/hugo/AppData/Local/Microsoft/WindowsApps/python3.exe

  is readable but not executable.  CMake is using it for compatibility.
Call Stack (most recent call first):
  /usr/share/cmake-4.2.1/Modules/FindPython3.cmake:671 (include)
  mbedtls/tf-psa-crypto/CMakeLists.txt:132 (find_package)
This warning is for project developers.  Use -Wno-dev to suppress it.

-- Could NOT find Python3 (missing: Interpreter)
    Reason given by package:
        Interpreter: Cannot run the interpreter "/cygdrive/c/Users/hugo/AppData/Local/Microsoft/WindowsApps/python3.exe"

=== Build error

CMake Error at mbedtls/library/CMakeLists.txt:342 (add_custom_command):
  Error evaluating generator expression:

    $<TARGET_SONAME_FILE_NAME:tfpsacrypto>

  TARGET_SONAME_FILE is not allowed for DLL target platforms.


CMake Error at mbedtls/library/CMakeLists.txt:342 (add_custom_command):
  Error evaluating generator expression:

    $<TARGET_SONAME_FILE_NAME:tfpsacrypto>

  TARGET_SONAME_FILE is not allowed for DLL target platforms.


CMake Error at mbedtls/library/CMakeLists.txt:342 (add_custom_command):
  Error evaluating generator expression:

    $<TARGET_SONAME_FILE_NAME:tfpsacrypto>

  TARGET_SONAME_FILE is not allowed for DLL target platforms.


CMake Error at mbedtls/library/CMakeLists.txt:342 (add_custom_command):
  Error evaluating generator expression:

    $<TARGET_SONAME_FILE_NAME:tfpsacrypto>

  TARGET_SONAME_FILE is not allowed for DLL target platforms.


CMake Error at mbedtls/library/CMakeLists.txt:342 (add_custom_command):
  Error evaluating generator expression:

    $<TARGET_SONAME_FILE_NAME:tfpsacrypto>

  TARGET_SONAME_FILE is not allowed for DLL target platforms.


CMake Error at mbedtls/library/CMakeLists.txt:342 (add_custom_command):
  Error evaluating generator expression:

    $<TARGET_SONAME_FILE_NAME:tfpsacrypto>

  TARGET_SONAME_FILE is not allowed for DLL target platforms.

Steps to reproduce

Install Cygwin on a Windows machine. Download http://www.leisink.net/hiawatha-12.0.tar.gz and unpack it. In the unpacked directory, use
mkdir build
cd build
cmake ..

Additional information

The Python warning was solved by adding "cmake_policy(SET CMP0109 NEW)" to tf-psa-crypto/CMakeLists.txt, which I already applied in the specified Hiawatha source. The problem is the TARGET_SONAME_FILE is not allowed for DLL target platforms. errors.

[gilles-peskine-arm]

CMP0109 was added in CMake 3.19. Mbed TLS 4.0 and TF-PSA-Crypto 1.0 officially require CMake 3.20.2 or later, but we still use older versions in our CI, so we can't just enable CMP0109.

But anyway that doesn't seem relevant for Cygwin, since it presents .exe files as executable. Does your installation mix some Cygwin and some non-Cygwin tools?

[Aethedor]

To build the software that uses mbed TLS, I only use the Cygwin versions of tools like cmake, make and gcc. No Cygwin-only tools are being used.

But the CMP0109 issue is not the show-stopper for me. It's everything below the '=== Build error' line.

[gilles-peskine-arm]

Ah, ok. Sorry, your original message was hard to read.

I guess there's some kind of Windows-specific thing that we're doing correctly in Windows native builds (since that's woking on our CI), but that we don't do on Cygwin even though we should? We aren't Cygwin experts so any insight would be appreciated.

[Aethedor]

Well, I'm no CMake expert, but I think the TARGET_SONAME_FILE refers to a library filename with .so extension. But Windows has .dll files, not .so files. I think that's why this goes wrong in Cygwin.