`FFI::Compiler::Loader.find` on Windows

[uvlad7]

Maybe my setup is wrong, but FFI::Compiler::Loader.find('ffi_llvm_jit_spec', './ext/ffi_llvm_jit_spec') fails on Windows, while the same but wrapped in File.absolute_path works

[davispuh]

Probably some bug. You can debug lib/ffi-compiler/loader.rb to see what exactly is happening.

[uvlad7]

@davispuh
Well, it works the same, I ran it in the project root

on windows mingw bash:

FFI::Compiler::Loader.find('ffi_llvm_jit_spec', './spec/ext/ffi_llvm_jit_spec')
=> "./spec/ext/ffi_llvm_jit_spec/x86_64-windows/ffi_llvm_jit_spec.dll"

on Ubuntu

FFI::Compiler::Loader.find('ffi_llvm_jit_spec', './spec/ext/ffi_llvm_jit_spec')
 => "./spec/ext/ffi_llvm_jit_spec/x86_64-linux/libffi_llvm_jit_spec.so" 

It's just that on Windows relative path doesn't work

module C; extend FFI::Library; end
=> C
C.ffi_lib "./spec/ext/ffi_llvm_jit_spec/x86_64-windows/ffi_llvm_jit_spec.dll"
C:/Ruby34-x64/lib/ruby/gems/3.4.0/gems/ffi-1.17.4-x64-mingw-ucrt/lib/ffi/dynamic_library.rb:94:in 'FFI::DynamicLibrary.load_library': Could not open library './spec/ext/ffi_llvm_jit_spec/x86_64-windows/ffi_llvm_jit_spec.dll': Failed with error 126: The specified module could not be  (LoadError)
.
Searched in <system library path>
        from C:/Ruby34-x64/lib/ruby/gems/3.4.0/gems/ffi-1.17.4-x64-mingw-ucrt/lib/ffi/library.rb:95:in 'block in FFI::Library#ffi_lib'
        from C:/Ruby34-x64/lib/ruby/gems/3.4.0/gems/ffi-1.17.4-x64-mingw-ucrt/lib/ffi/library.rb:94:in 'Array#map'
        from C:/Ruby34-x64/lib/ruby/gems/3.4.0/gems/ffi-1.17.4-x64-mingw-ucrt/lib/ffi/library.rb:94:in 'FFI::Library#ffi_lib'
        from (irb):2:in '<main>'
        from <internal:kernel>:168:in 'Kernel#loop'
        from bin/console:27:in '<main>'
File.exist? "./spec/ext/ffi_llvm_jit_spec/x86_64-windows/ffi_llvm_jit_spec.dll"
=> true
C.ffi_lib File.absolute_path("./spec/ext/ffi_llvm_jit_spec/x86_64-windows/ffi_llvm_jit_spec.dll")
=> [#<FFI::DynamicLibrary:0x00000241f7de5900 @name="Z:/spec/ext/ffi_llvm_jit_spec/x86_64-windows/ffi_llvm_jit_spec.dll">]

only works when current dir is added as dll directory:

RubyInstaller::Runtime.add_dll_directory '.'
=> #<RubyInstaller::Runtime::DllDirectory:0x000001c3c31f44a0 @handle=1940298939840, @path="Z:/">
module C; extend FFI::Library; end
=> C
C.ffi_lib "./spec/ext/ffi_llvm_jit_spec/x86_64-windows/ffi_llvm_jit_spec.dll"
=> [#<FFI::DynamicLibrary:0x000001c3c32b3aa8 @name="./spec/ext/ffi_llvm_jit_spec/x86_64-windows/ffi_llvm_jit_spec.dll">]

but on Linux and macOS it works

module C; extend FFI::Library; end
 => C 
C.ffi_lib "./spec/ext/ffi_llvm_jit_spec/x86_64-linux/libffi_llvm_jit_spec.so"
 => [#<FFI::DynamicLibrary:0x00007c23d9263418 @name="./spec/ext/ffi_llvm_jit_spec/x86_64-linux/libffi_llvm_jit_spec.so">] 

So what I suggest is either:

• Change the examples to use File.absolute_path
• Add a note that either File.absolute_path or RubyInstaller::Runtime.add_dll_directory is needed on Windows
• Change FFI::Compiler::Loader.find to return absolute paths

[davispuh]

Okay so this is not actually ffi-compiler issue but a bug in ffi in Windows.
See ffi/ext/ffi_c/DynamicLibrary.c:223.
Don't know how exactly it works but reading https://learn.microsoft.com/en-us/windows/win32/api/libloaderapi/nf-libloaderapi-loadlibraryexa it says:

If lpFileName specifies a relative path, the entire relative path is appended to every token in the DLL search path. To load a module from a relative path without searching any other path, use GetFullPathName to get a nonrelative path and call LoadLibraryEx with the nonrelative path. If the module is being loaded as a datafile and the relative path starts with "." or "..", the relative path is treated as an absolute path.

So maybe in Windows working directory is not part of DLL search path in which case it wouldn't be found.
My suggestion would be submit PR to ffi :)

[uvlad7]

ffi already kinda acknowledges that and the ffi's approach is to rely on the dynamic loader's behavior, so I believe it's the intended behavior