[DynInst_API:] Struct size computation

[Fabian Mager <fabian.mager@xxxxxxxxxxxxxx>]

Hello all,

my goal is to extract parameter values of function calls and therefore I 
use getLocalVariableValue(...). This works quite well so far but not in 
case the parameter is a struct. getLocalVariableValue() uses 
Type::getSize() which calls typeStruct::updateSize() in case of a 
struct. This method just calculates the sum of the sizes of all struct 
elements. The problem I have is when padding comes into play, e.g.:
struct st {
    int i;    // 4 Bytes
    char c;   // 1 Byte + 3 Bytes padding
    float f;  // 4 Bytes
}

The size of struct st is 12 Bytes on my machine but getSize() returns 9. 
getLocalVariableValue() uses this wrong size to fill the result buffer 
with 9 Bytes of information. This buffer then contains the 3 Bytes of 
padding but not the last 3 Bytes of the float. Nevertheless, 
getLocalVariableValue() returns 0 to indicate everything went well, even 
if thats obviously not the case. In order to solve that I made a little 
patch that considers padding within the struct but not at the end (which 
is fine for me so far). I'm really not an expert in DynInst so I don't 
know if this breaks something or not. Perhaps I miss something that 
already solves my problem?
--- a/symtabAPI/src/Type.C
+++ b/symtabAPI/src/Type.C

@@ -197,7 +197,9 @@ unsigned int Type::getSize()
{
-       if (!size_)
+   // If default constructed, update
+   if (!size_ || (size_ == sizeof(int)))
        const_cast<Type *>(this)->updateSize();
    return size_;
}

@@ -896,15 +898,25 @@ void typeStruct::updateSize()
    // Calculate the size of the entire structure
    size_ = 0;
-   for(unsigned int i = 0; i < fieldList.size(); ++i) {
-       size_ += fieldList[i]->getSize();

-       // Is the type of this field still a placeholder?
-       if(fieldList[i]->getType()->getDataClass() == dataUnknownType) {
-           size_ = 0;
-           break;
-       }
-   }
+
+   // considers padding
+   Field* lastElement = fieldList.back();
+   size_ = (lastElement->getOffset() / 8) + lastElement->getSize();

Best regards,
Fabian