Avoid struct-by-value argument for rb_thread_wait_for()

* struct by value arguments are not well supported from NFI to Sulong,
  sometimes it works by chance due to how it is compiled to bitcode.
* This is the only struct-by-value argument in the C API subset we implement.

Author: eregon

lib/cext/include/ruby/internal/intern/thread.h

@@ -196,7 +196,14 @@ VALUE rb_thread_create(VALUE (*f)(void *g), void *g);
  * @param[in]  time           Duration.
  * @exception  rb_eInterrupt  Interrupted.
  */
+#ifdef TRUFFLERUBY
+void rb_tr_thread_wait_for(struct timeval* time);
+static inline void rb_thread_wait_for(struct timeval time) {
+    rb_tr_thread_wait_for(&time);
+}
+#else
 void rb_thread_wait_for(struct timeval time);
+#endif
 
 /**
  * Obtains the "current" thread.

src/main/c/cext/thread.c

@@ -29,8 +29,8 @@ VALUE rb_thread_local_aset(VALUE thread, ID id, VALUE val) {
   return RUBY_INVOKE(thread, "[]=", ID2SYM(id), val);
 }
 
-void rb_thread_wait_for(struct timeval time) {
-  double seconds = (double)time.tv_sec + (double)time.tv_usec/1000000;
+void rb_tr_thread_wait_for(struct timeval* time) {
+  double seconds = (double)time->tv_sec + (double)time->tv_usec/1000000;
   polyglot_invoke(rb_tr_unwrap(rb_mKernel), "sleep", seconds);
 }
 

tool/generate-cext-trampoline.rb

@@ -55,13 +55,17 @@
   functions.concat found_functions
 end
 
+def struct_by_value?(type)
+  type =~ /\bstruct\b/ and !type.include?('*')
+end
+
 functions.each do |declaration, return_type, function_name, argument_types|
   raise declaration if /\bstatic\b/ =~ declaration
   raise declaration if function_name.start_with?('rb_tr_init') and function_name != 'rb_tr_init_exception'
   if declaration.include? "\n"
     abort "This declaration includes newlines but should not:\n#{declaration}\n\n"
   end
-  if return_type =~ /\bstruct\s/ and !return_type.include?('*')
+  if struct_by_value? return_type
     abort "Returning a struct by value from Sulong to NFI is not supported for:\n#{declaration}"
   end
 end
@@ -188,6 +192,10 @@
     argument_names = argument_types.delete_prefix('(').delete_suffix(')')
     argument_names = argument_names.scan(/(?:^|,)\s*(#{argument_regexp})\s*(?=,|$)/o)
     argument_names = argument_names.map { |full_arg, name1, name2|
+      if struct_by_value? full_arg
+        abort "struct by value argument not well supported from NFI to Sulong: #{full_arg}\n#{declaration}"
+      end
+
       if full_arg == "void"
         ""
       elsif full_arg == "..."