ffi: add LibFFI-based foreign function interface module

.github/workflows/debian.yml

@@ -16,7 +16,7 @@ jobs:
       - name: Install dependencies
         run: |
           sudo apt update
-          sudo apt install devscripts build-essential lintian libjson-c-dev debhelper-compat debhelper cmake
+          sudo apt install devscripts build-essential lintian libjson-c-dev debhelper-compat debhelper cmake libffi-dev
 
       - name: Build package
         run: |

.opencode/skills/ucode/SKILL.md

@@ -0,0 +1,55 @@
+---
+name: ucode
+description: Build, test, and execute ucode programs using cmake, the ucode compiler, and the custom test suite
+metadata:
+  audience: developers
+  workflow: development
+---
+
+## What I do
+
+I handle the common workflows for working with the ucode scripting language project: building from source, running tests, and executing ucode with libraries.
+
+## Build
+
+Configure the build (run this first if CMake files changed):
+```bash
+cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug
+```
+
+Compile:
+```bash
+make -C build
+```
+
+## Test
+
+Run the entire test suite:
+```bash
+./tests/custom/run_tests.uc
+```
+
+Run tests in a specific directory (note the trailing wildcard pattern):
+```bash
+./tests/custom/run_tests.uc tests/custom/17_lib_ffi/*
+```
+
+## Execute
+
+Run a ucode snippet with a loaded library:
+```bash
+./build/ucode -L build -l ffi -e 'print(ffi.C.dlsym("size_t"))'
+```
+
+Key flags:
+- `-L <path>` — prepend path to library search directory
+- `-l <name>` — preload a library (e.g. `ffi`, `json`, `uci`)
+- `-e '<expr>'` — execute an expression inline
+
+## When to use me
+
+Use this skill when the user wants to:
+- Build or rebuild the ucode project
+- Run the test suite (all or specific subdirectories)
+- Execute ucode code snippets with or without loading custom libraries
+- Debug ucode issues by running code interactively

CMakeLists.txt

@@ -4,6 +4,8 @@ project(ucode C)
 
 add_library(uc_defines INTERFACE)
 
+list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
+
 include(CheckFunctionExists)
 include(CheckSymbolExists)
 include(CheckCSourceCompiles)
@@ -76,6 +78,7 @@ find_library(libubus NAMES ubus)
 find_library(libblobmsg_json NAMES blobmsg_json)
 find_package(ZLIB)
 find_library(libmd NAMES libmd.a md)
+find_library(libffi NAMES ffi)
 
 if(LINUX)
   find_library(libnl_tiny NAMES nl-tiny)
@@ -105,10 +108,15 @@ if(libmd)
   set(DEFAULT_DIGEST_SUPPORT ON)
 endif()
 
+if(libffi)
+  set(DEFAULT_FFI_SUPPORT ON)
+endif()
+
 option(DEBUG_SUPPORT "Debug plugin support" ON)
 option(FS_SUPPORT "Filesystem plugin support" ON)
 option(IO_SUPPORT "IO plugin support" ON)
 option(MATH_SUPPORT "Math plugin support" ON)
+option(FFI_SUPPORT "FFI module support" ${DEFAULT_FFI_SUPPORT})
 option(UBUS_SUPPORT "Ubus plugin support" ${DEFAULT_UBUS_SUPPORT})
 option(UCI_SUPPORT "UCI plugin support" ${DEFAULT_UCI_SUPPORT})
 option(RTNL_SUPPORT "Route Netlink plugin support" ${DEFAULT_NL_SUPPORT})
@@ -407,6 +415,29 @@ if(DIGEST_SUPPORT)
   target_link_libraries(digest_lib ${libmd})
 endif()
 
+if(FFI_SUPPORT)
+  pkg_check_modules(LIBFFI REQUIRED libffi)
+  include_directories(${LIBFFI_INCLUDE_DIRS})
+  set(LIBRARIES ${LIBRARIES} ffi_lib)
+  add_library(ffi_lib MODULE lib/ffi/uc_cparse.c lib/ffi/uc_ctype.c lib/ffi/uc_cconv.c lib/ffi/uc_cdata.c lib/ffi/ffi.c)
+  set_target_properties(ffi_lib PROPERTIES OUTPUT_NAME ffi PREFIX "")
+
+  set(CMAKE_REQUIRED_INCLUDES ${LIBFFI_INCLUDE_DIRS})
+  set(CMAKE_REQUIRED_LIBRARIES ${LIBFFI_LIBRARIES})
+
+  check_c_source_compiles("
+    #include <ffi.h>
+    int main() { return FFI_BAD_ARGTYPE; }
+  " HAVE_FFI_BAD_ARGTYPE)
+
+  if(HAVE_FFI_BAD_ARGTYPE)
+    target_compile_definitions(ffi_lib PRIVATE HAVE_FFI_BAD_ARGTYPE)
+  endif()
+
+  target_link_options(ffi_lib PRIVATE ${UCODE_MODULE_LINK_OPTIONS})
+  target_link_libraries(ffi_lib ${LIBFFI_LINK_LIBRARIES})
+endif()
+
 if(UNIT_TESTING)
   enable_testing()
   add_compile_definitions( UNIT_TESTING )