# \`ffi-lib\` fails to load an existing library **URL:** \ **Category:** Questions & Answers\ **Tags:** question, ffi\ **Created:** [September 30, 2023, 3:30pm UTC](https://racket.discourse.group/t/ffi-lib-fails-to-load-an-existing-library/2353 "2023-09-30T15:30:17Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Antigen-11](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/antigen-11/32/1813_2.png) [@Antigen-11](https://racket.discourse.group/u/Antigen-11)\ **Post date:** [September 30, 2023, 3:30pm UTC](https://racket.discourse.group/t/ffi-lib-fails-to-load-an-existing-library/2353/1 "2023-09-30T15:30:17Z")
Hello, everyone! I create an application and use [The Racket Foreign Interface](https://docs.racket-lang.org/foreign/index.html) to load foreign libraries. Here's part of the project after compiling c codes. ```scheme ./gsl-fork/build/lib/ ├── libgsl.a ├── libgslcblas.a ├── libgslcblas.la ├── libgslcblas.so -> libgslcblas.so.0.0.0 ├── libgslcblas.so.0 -> libgslcblas.so.0.0.0 ├── libgslcblas.so.0.0.0 ├── libgsl.la ├── libgsl.so -> libgsl.so.25.1.0 ├── libgsl.so.25 -> libgsl.so.25.1.0 ├── libgsl.so.25.1.0 └── pkgconfig └── gsl.pc ``` And I have a `library.rkt` in the root directory. ```scheme #lang racket/base (require racket/runtime-path ffi/unsafe setup/dirs (for-syntax racket/base)) (define-runtime-path lib-dir (build-path "gsl-fork" "build" "lib")) (define (find-ffi-lib name version) (ffi-lib name (list version #f) #:get-lib-dirs (lambda () (cons lib-dir (get-lib-search-dirs))))) (define libgsl (find-ffi-lib "libgsl" "25.1.0")) (define libgslblas (find-ffi-lib "libgslcblas" "0.0.0")) ``` When I execute `racket library.rkt`, `ffi-lib` reports an error. It seems that the shared object is not found. ```scheme ffi-lib: could not load foreign library path: libgsl.so.25.1.0 system error: libgsl.so.25.1.0: 无法打开共享对象文件: 没有那个文件或目录 context...: /home/hin/racket/collects/ffi/unsafe.rkt:131:0: get-ffi-lib body of "/home/hin/repo/racket-gsl/library.rkt" ``` Maybe there's something I've never learnt about. So I run two tests in racket REPL. ```scheme > ,r ffi/unsafe > (current-directory "gsl-fork/build/lib") ; now in /home/hin/repo/racket-gsl/gsl-fork/build/lib > (define cblas (ffi-lib "libgslcblas.so" "0.0.0")) > (define gsl (ffi-lib "libgsl.so" "25.1.0")) ffi-lib: could not load foreign library path: libgsl.so.25.1.0 system error: libgsl.so.25.1.0: 无法打开共享对象文件: 没有那个文件或目录 [,bt for context] ``` As I expect, `ffi-lib` cannot find `libgsl.so.25.1.0`. But it does successfully load `libgslcblas.so.0.0.0`. Would you please explain the situation to me? What can I do to repair this? Yours frankly. Antigen-11 ---
**Author:** ![soegaard](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/soegaard/32/19_2.png) [@soegaard](https://racket.discourse.group/u/soegaard)\ **Post date:** [September 30, 2023, 5:13pm UTC](https://racket.discourse.group/t/ffi-lib-fails-to-load-an-existing-library/2353/2 "2023-09-30T17:13:39Z")
It looks like it could be related to the search path for shared libraries. - Have you tried an absolute path for testing? If it works, then there is some other thigs to try: - Does it work if you move the shared library to one of the directories listed in `(get-lib-search-dirs)`? - What's the value of `lib-dir` and what do you see when you run `ls` in the directory? ---
**Author:** ![Antigen-11](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/antigen-11/32/1813_2.png) [@Antigen-11](https://racket.discourse.group/u/Antigen-11)\ **Post date:** [October 1, 2023, 2:07am UTC](https://racket.discourse.group/t/ffi-lib-fails-to-load-an-existing-library/2353/3 "2023-10-01T02:07:13Z")
> [@soegaard](#): > > Have you tried an absolute path for testing? Yes, I have. `racket library.rkt` still fails when I use `(define-runtime-path lib-dir (path->complete-path (build-path "gsl-fork" "build" "lib")))`. > [@soegaard](#): > > Does it work if you move the shared library to one of the directories listed in `(get-lib-search-dirs)`? No, it doesn't work. > [@soegaard](#): > > What's the value of `lib-dir` and what do you see when you run `ls` in the directory? ```scheme > ,en "library.rkt" ffi-lib: could not load foreign library path: libgsl.so.25.1.0 system error: libgsl.so.25.1.0: 无法打开共享对象文件: 没有那个文件或目录 [,bt for context] "library.rkt"> lib-dir # ``` ```scheme ~/repo/racket-gsl/gsl-fork/build/lib$ ls . libgsl.a libgslcblas.so libgsl.la libgsl.so.25.1.0 libgslcblas.a libgslcblas.so.0 libgsl.so pkgconfig libgslcblas.la libgslcblas.so.0.0.0 libgsl.so.25 ``` ---
**Author:** ![soegaard](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/soegaard/32/19_2.png) [@soegaard](https://racket.discourse.group/u/soegaard)\ **Post date:** [October 1, 2023, 10:57am UTC](https://racket.discourse.group/t/ffi-lib-fails-to-load-an-existing-library/2353/4 "2023-10-01T10:57:11Z")
> > Have you tried an absolute path for testing? I meant tried ```scheme (ffi-lib absolute-path-to-shared-library) ``` > > Does it work if you move the shared library to one of the directories listed in `(get-lib-search-dirs)` ? > > No, it doesn't work. Can you load your shared library from another programming language, like C? Another thing to try: Rename it something simple like `foo.so` without version numbers. Will it load now? [Maybe it's not the search path that's the problem, maybe it's the version number?] ---
**Author:** ![ryanc](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/ryanc/32/71_2.png) [@ryanc](https://racket.discourse.group/u/ryanc)\ **Post date:** [October 1, 2023, 3:50pm UTC](https://racket.discourse.group/t/ffi-lib-fails-to-load-an-existing-library/2353/5 "2023-10-01T15:50:12Z")
Two suggestions: First, `ffi-lib` logs about its library searches on the `ffi-lib` topic. So if you start racket with, for example, ``` $ PLTSTDERR="debug@ffi-lib error" racket ``` then you'll get messages to stderr about what paths `ffi-lib` tried in order to find the library. Unfortunately, the most common reason for `ffi-lib` failing is that it finds the right file, but it is unable to load some dependency, and the OS doesn't have a portable interface for finding out why (IIRC). So the logging might not tell you much in this case. Second, if this is on Linux, you can run the command `ldd` on your shared object file. It will print the library's dependencies and how they would be resolved given the OS search path. If you have unresolved dependencies, it might (?) work to load them explicitly first with `ffi-lib`, but I'm not sure. But that's the best way I know to diagnose a failure to load because of unresolved dependencies. ---
**Author:** ![Antigen-11](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/antigen-11/32/1813_2.png) [@Antigen-11](https://racket.discourse.group/u/Antigen-11)\ **Post date:** [October 1, 2023, 3:59pm UTC](https://racket.discourse.group/t/ffi-lib-fails-to-load-an-existing-library/2353/6 "2023-10-01T15:59:13Z")
Python logs an error, too. ```scheme >>> from ctypes import * >>> lib = cdll.LoadLibrary("gsl-fork/build/lib/libgsl.so") Traceback (most recent call last): File "", line 1, in File "/usr/lib/python3.10/ctypes/ __init__.py", line 452, in LoadLibrary return self._dlltype(name) File "/usr/lib/python3.10/ctypes/ __init__.py", line 374, in __init__ self._handle = _dlopen(self._name, mode) OSError: gsl-fork/build/lib/libgsl.so: undefined symbol: cblas_ctrmv ``` There is a symbol defined in `libgslcblas.so`, so I need to load it globally first. ```scheme > ,r ffi/unsafe > ;;Load libgslcblas globally (define libgslcblas (ffi-lib "gsl-fork/build/lib/libgslcblas" #:global? #t)) > (define libgsl (ffi-lib "gsl-fork/build/lib/libgsl")) > ``` I manage to load `libgsl.so` now. But the error message of racket really confuses me. It is not that `ffi-lib` cannot find the library, but that there is an undefined symbol. ---
**Author:** ![Antigen-11](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/antigen-11/32/1813_2.png) [@Antigen-11](https://racket.discourse.group/u/Antigen-11)\ **Post date:** [October 1, 2023, 4:04pm UTC](https://racket.discourse.group/t/ffi-lib-fails-to-load-an-existing-library/2353/7 "2023-10-01T16:04:42Z")
Thanks! I learnt a lot from your suggestions. ---
**Author:** ![Antigen-11](https://yyz2.discourse-cdn.com/free1/user_avatar/racket.discourse.group/antigen-11/32/1813_2.png) [@Antigen-11](https://racket.discourse.group/u/Antigen-11)\ **Post date:** [October 1, 2023, 4:19pm UTC](https://racket.discourse.group/t/ffi-lib-fails-to-load-an-existing-library/2353/8 "2023-10-01T16:19:40Z")
> [@ryanc](#): > > Unfortunately, the most common reason for `ffi-lib` failing is that it finds the right file, but it is unable to load some dependency, and the OS doesn't have a portable interface for finding out why (IIRC). So the logging might not tell you much in this case. I run `PLTSTDERR="debug@ffi-lib error" racket library.rkt` and then get some messages. ```scheme ffi-lib: failed for (ffi-lib "libgsl" '("25.1.0" #f)), tried: # (exists) # (exists) # (no such file) # (no such file) # (no such file) # (no such file) # (no such file) # (no such file) # (no such file) "libgsl.so.25.1.0" (using OS library search path) "libgsl.so" (using OS library search path) "libgsl" (using OS library search path) # (no such file) # (no such file) # (no such file) ``` `ffi-lib` does find the library. And according to the documentation, this is expected behaviour. > A library file may exist but fail to load for some reason; the eventual error message will unfortunately name the fallback from the second or third bullet, since some operating systems offer no way to determine why a given library path failed.