RFR(L): 8180032: Unaligned pointer dereference in ClassFileParser

[Robbin Ehn]

Hi,

On 05/17/2017 03:46 AM, Kim Barrett wrote:
>> On May 9, 2017, at 6:40 PM, Mikael Vidstedt <mikael.vidstedt at oracle.com> wrote:
>>
>>
>> Warning: It may be wise to stock up on coffee or tea before reading this.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8180032
>> Webrev: http://cr.openjdk.java.net/~mikael/webrevs/8180032/webrev.00/hotspot/webrev/ <http://cr.openjdk.java.net/~mikael/webrevs/8180032/webrev.00/hotspot/webrev/>
> 
> Not a review, just a question.
> 
> ------------------------------------------------------------------------------
> src/cpu/x86/vm/bytes_x86.hpp
>    40   template <typename T>
>    41   static inline T get_native(const void* p) {
>    42     assert(p != NULL, "null pointer");
>    43
>    44     T x;
>    45
>    46     if (is_ptr_aligned(p, sizeof(T))) {
>    47       x = *(T*)p;
>    48     } else {
>    49       memcpy(&x, p, sizeof(T));
>    50     }
>    51
>    52     return x;
> 
> I'm looking at this and wondering if there's a good reason to not just
> unconditionally use memcpy here.  gcc -O will generate a single move
> instruction for that on x86_64.  I'm not sure what happens on 32bit
> with an 8 byte value, but I suspect it will do something similarly
> sensible, e.g. 2 4 byte memory to memory transfers.

Unconditionally memcpy would be nice!

Are going to look into that Mikael?

/Robbin

> 
> ------------------------------------------------------------------------------
>