using approach with dummy struct for va_args

Author: aodinokov

examples/c_ffi_call/value_ffi.c

@@ -121,7 +121,6 @@ static int _val_to_ffi_type(metac_entry_t * p_entry, metac_flag_t variadic, ffi_
             return -ENOMEM;
         }
 #if __linux__
-        va_list x;
         p_ffi_type->type = FFI_TYPE_STRUCT;
         p_ffi_type->size = sizeof(void*);
         p_ffi_type->alignment = p_ffi_type->size;

modules/metac-reflect-gen/templates/_struct_type.tpl

@@ -7,51 +7,12 @@
 {{-          $declaraion := false -}}
 {{-          with $v.ByteSize -}}
 {{-            $sz := toJson . }}
-// size {{ $sz }}
+struct _dummy_{{ $i }} { char _data_[ {{ $sz }} ]; };
 static metac_flag_t {{ $i }}_va_arg(struct va_list_container *p_va_list_container, void * buf) {
     if (p_va_list_container != NULL && buf != NULL) {
-{{- /* 
-
-This code is done this way in order to avoid an issue faced with Windows: 
-if the structure has size 1,2,4 or 8 (potentially 16 for some platforms)
-va_arg(p_va_list_container->parameters, char[<size>]) just fails.
-but it works for other sizes.
-Also it workes ok for Linux and Mac. for now only Windows has this issue.
-the WA demonstrated here works ok for our tests.
-
-In general it appears that va_list is very specific to platform
-and has many issues when you try to use it for structures (not pointers).
-*/ -}}
-{{-            if eq "1" $sz }}
-        uint8_t data = va_arg(p_va_list_container->parameters, int);
-        memcpy(buf, &data, {{ . }});
+        struct _dummy_{{ $i }} v = va_arg(p_va_list_container->parameters, struct _dummy_{{ $i }});
+        memcpy(buf, &v, {{$sz}});
         return 1;
-{{-            else if eq "2" $sz }}
-        uint16_t data = va_arg(p_va_list_container->parameters, int);
-        memcpy(buf, &data, {{ . }});
-        return 1;
-{{-            else if eq "4" $sz }}
-        uint32_t data = va_arg(p_va_list_container->parameters, uint32_t);
-        memcpy(buf, &data, {{ . }});
-        return 1;
-{{-            else if eq "8" $sz }}
-        uint64_t data = va_arg(p_va_list_container->parameters, uint64_t);
-        memcpy(buf, &data, {{ . }});
-        return 1;
-{{-            else }}
-        long long data;
-        if (sizeof(data) == {{ . }}) {
-            data = va_arg(p_va_list_container->parameters, long long);
-            memcpy(buf, &data, {{ . }});
-            return 1;
-        }
-        void * p = (void*) va_arg(p_va_list_container->parameters, char[{{ . }}]);
-        if (p == NULL) {
-            return 0;
-        }
-        memcpy(buf, p, {{ . }});
-        return 1;
-{{-            end }}
     }
     return 0;
 }