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

[Kim Barrett]

> 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.

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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.

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