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

[Mark Kettenis <kettenis@chello.nl>]

   Date: Thu, 26 Feb 2004 20:22:11 -0500
   From: Andrew Cagney <ac131313@redhat.com>

   Hello,

   For a 64-bit gregset, the code was only modifying the low 32-bits of the 
   register field - leaving the upper 64-bits undefined.

That's not completely unintentional.  The idea is to leave any
"reserved" bits untouched, and in a sense for 32-bit stuff the upper
32 bits are "reserved"; they are not necessarily zero, at least not
for all registers.

To prevent the upper 32 bits being "undefined", typical usage of these
functions is:

      ptrace (PT_GETREGS, ..., &regs, 0);

      amd64_collect_native_gregset (current_regcache, &regs, regnum);

      ptrace (PT_SETREGS, ..., &regs, 0);

   This, among other things, would lead to mysterious 32-bit thread
   failures.

I guess the thread code isn't doing the equivalent of the PT_GETREGS
call.  I think the correct way to fix this is to make sure the buffer
is properly initialized before you pass it to
amd64_collect_native_gregset.

Another problem with your patch is that I'd rather like avoid assuming
that the register buffer is an array of 8-byte registers.

Mark