Re: [rfa/amd64] Zero fill 32-bit registers

[Andrew Cagney <cagney@gnu.org>]

>    It doesn't address the underlying problem where fetching an individual 
>    register leaves half the register field undefined.   The code shouldn't 
>    assume that other code has magically initialized the rest of that 
>    register field.
> 
> OK, but you realize its the problem of the threads code, and *not* the
> code amd64-nat.c?

Both are broken - "society is to blame".

>    >    > Another problem with your patch is that I'd rather like avoid assuming
>    >    > that the register buffer is an array of 8-byte registers.
>    > 
>    >    That code already assumems that, and that the values are little-endian.
>    > 
>    > Yes it assumes little-endianness, but the assumptions on the size of
>    > the slots in the register buffer are weaker.  The register buffer here
>    > corresponds to `struct reg' on the BSD's.  It would be prefectly well
>    > possible for some of its members to be 4 bytes in size.  The current
>    > code works for that case, whereas with your patch, it could thrash
>    > another member of the structure.
> 
>    Do you know of any such an system?
> 
> Actually GNU/Linux x86-64 has a gregset_t where %cs, %fs and %gs are
> stored in a short.
> 
> Could you live with just zero-extending the 16 general-purpose
> registers and the instruction pointer?  I'll implement it for you.

It is certainly an improvement!  Can you test it?

Andrew