fix: make lean4 build on FreeBSD

src/CMakeLists.txt

@@ -352,6 +352,11 @@ if(${CMAKE_SYSTEM_NAME} MATCHES "Linux")
   string(APPEND LEANC_EXTRA_FLAGS " -fPIC")
   string(APPEND LEANSHARED_LINKER_FLAGS " -Wl,-rpath=\\$$ORIGIN/..:\\$$ORIGIN")
   string(APPEND CMAKE_EXE_LINKER_FLAGS " -lleanshared -Wl,-rpath=\\\$ORIGIN/../lib:\\\$ORIGIN/../lib/lean")
+elseif(${CMAKE_SYSTEM_NAME} MATCHES "FreeBSD")
+  string(APPEND CMAKE_CXX_FLAGS " -fPIC -ftls-model=initial-exec")
+  string(APPEND LEANC_EXTRA_FLAGS " -fPIC")
+  string(APPEND LEANSHARED_LINKER_FLAGS " -Wl,-rpath=\\$$ORIGIN/..:\\$$ORIGIN")
+  string(APPEND CMAKE_EXE_LINKER_FLAGS " -lleanshared -Wl,-rpath=\\\$ORIGIN/../lib:\\\$ORIGIN/../lib/lean")
 elseif(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
   string(APPEND CMAKE_CXX_FLAGS " -ftls-model=initial-exec")
   string(APPEND LEANSHARED_LINKER_FLAGS " -install_name @rpath/libleanshared.dylib")

src/runtime/io.cpp

@@ -855,7 +855,13 @@ extern "C" LEAN_EXPORT obj_res lean_io_app_path(obj_arg) {
     char dest[PATH_MAX];
     memset(dest, 0, PATH_MAX);
     pid_t pid = getpid();
-    snprintf(path, PATH_MAX, "/proc/%d/exe", pid);
+#if defined(__linux__)
+     snprintf(path, PATH_MAX, "/proc/%d/exe", pid);
+#elif defined(__FreeBSD__)
+    snprintf(path, PATH_MAX, "/proc/%d/file", pid);
+#else
+#   error "Unknown platform"
+#endif
     if (readlink(path, dest, PATH_MAX) == -1) {
         return io_result_mk_error("failed to locate application");
     } else {

src/runtime/stack_overflow.cpp

@@ -20,6 +20,11 @@ Port of the corresponding Rust code (see links below).
 #include <lean/lean.h>
 #include "runtime/stack_overflow.h"
 
+#if defined(__FreeBSD__)
+#    include <pthread_np.h>
+#    define pthread_getattr_np pthread_attr_get_np
+#endif
+
 namespace lean {
 // stack guard of the main thread
 static stack_guard * g_stack_guard;