ldd-deploy for MSYS2 UCRT64

ucrt_ldd_deploy.sh collects the runtime DLL dependencies of an MSYS2 UCRT64 executable into a deployment directory. This is useful when an application runs inside MSYS2 but fails on another Windows machine because MinGW/UCRT64 libraries such as libstdc++-6.dll, libgcc_s_seh-1.dll, or third-party library DLLs are not installed there.

The script does not modify the executable or create an installer. It builds the application's DLL directory so that the executable and its non-system runtime dependencies can be distributed together.

Run the script from an MSYS2 UCRT64 shell. It uses:

• Bash
• MSYS2's ldd
• grep, awk, and xargs
• cygpath when ldd reports a Windows-style path
• cp

The executable must already be built, and all of its dependencies must be installed and discoverable in the current MSYS2 environment.

./ucrt_ldd_deploy.sh -i <executable> [-o <output-directory>] [-u <ucrt-bin-directory>]

For example:

./ucrt_ldd_deploy.sh \
  --input ./build/myapp.exe \
  --output ./package

To make a directory that can be copied directly to another Windows machine, first put the executable in it and then collect its DLLs into the same directory:

mkdir -p ./package
cp ./build/myapp.exe ./package/
./ucrt_ldd_deploy.sh -i ./build/myapp.exe -o ./package

The resulting layout is similar to:

package/
|-- myapp.exe
|-- libgcc_s_seh-1.dll
|-- libstdc++-6.dll
|-- libwinpthread-1.dll
`-- <other project dependencies>.dll

The exact DLL list depends on the compiler, packages, and libraries used by the project.

If the UCRT64 installation is in a nonstandard location, override its bin directory explicitly:

./ucrt_ldd_deploy.sh \
  -i ./build/myapp.exe \
  -o ./package \
  -u /c/tools/msys64/ucrt64/bin

1. It parses the input, output, and optional UCRT bin directory arguments.
2. It creates the output directory with mkdir -p.
3. It runs ldd on the input executable. ldd asks the MSYS2 loader to report the DLLs required by the executable and its linked libraries.
4. It removes dependency lines containing windows (case-insensitive). These normally point into the Windows system directory and should be supplied by Windows, not bundled with the application.
5. For each remaining name => path mapping, it extracts the DLL name and the resolved source path.
6. It first looks for that name in the selected UCRT64 bin directory. If it is not there, it uses the path reported by ldd. If that path is in Windows form, such as C:\\msys64\\ucrt64\\bin\\example.dll, cygpath -u converts it to an MSYS2 path before the file is checked.
7. It copies the DLL to the output directory with cp -u. An existing destination file is replaced only when the source is newer, and each successful copy is printed.

Searching the configured UCRT64 bin directory first is important: it selects the DLL built for the active UCRT64 toolchain when a similarly named DLL is also available in another MSYS2 environment such as MINGW64 or CLANG64.

Build and deploy from the same UCRT64 environment so that ldd, $MINGW_PREFIX, and the installed DLLs all refer to the same toolchain. A common workflow is:

# Run these commands in the MSYS2 UCRT64 shell.
cmake -S . -B build -G Ninja
cmake --build build

mkdir -p package
cp build/myapp.exe package/
./ucrt_ldd_deploy.sh -i build/myapp.exe -o package

If the project produces several executables, run the script once for each one and use the same output directory. Because the script uses cp -u, shared DLLs do not needlessly get recopied:

./ucrt_ldd_deploy.sh -i build/myapp.exe -o package
./ucrt_ldd_deploy.sh -i build/myhelper.exe -o package

Test the package from a normal Windows terminal, preferably on a machine or VM without MSYS2 on PATH. That confirms the application is loading the packaged DLLs instead of silently finding DLLs in the development environment.

• The script only sees libraries reported by ldd. Plugins and DLLs loaded at runtime with LoadLibrary, dlopen, configuration, or user actions may need to be copied separately.
• Windows system DLLs are intentionally excluded. Do not redistribute DLLs from the Windows system directory as application dependencies.
• A missing dependency cannot be copied. Run ldd ./path/to/app.exe directly if a required DLL does not appear in the package, then install or locate the matching UCRT64 package.
• DLL redistribution may be governed by the dependency's license. Review the licenses of third-party libraries before publishing a package.
• Paths containing spaces should be quoted when invoking the script.

The repository also contains alternative Bash and C++ implementations; this document focuses on ucrt_ldd_deploy.sh and the MSYS2 UCRT64 workflow.