sparc64/-m64 support?

[Nathan Myers <ncm-nospam at cantrip dot org>]

I have been scouring the docs for details about building gcc --
specifically, g++ and libstdc++ -- to produce sparc64 binaries.

The docs I have found that mention sparc64 are ambiguous.  They
give the impression that one compiler can produce both -m32 and
-m64 .o files, using multilibs for different models.  However, in 
"http://gcc.gnu.org/install/specific.html#sparc64-*-*"; it says, 

  GCC version 2.95 is not able to compile code correctly for sparc64 
  targets. Users of the Linux kernel, at least, can use the sparc32 
  program to start up a new shell invocation with an environment that 
  causes configure to recognize (via uname -a) the system as sparc-*-*
  instead."  

I don't know how to interpret that; the gcc-3.0.x that I build on the 
ultrasparc is built with a gcc-2.95.

The best detailed note I found was

  http://gcc.gnu.org/ml/libstdc++/2001-09/msg00128.html

which hints that on 3.0.3 it might actually work, given the right
incantations (which are?).

Who has experience with building and using g++ to compile runnable
"-m64" binaries?  In particular,

1. What surprises are in store, and what should I expect not to work?  
2. Do I need any special options besides "-m64" (e.g. "-mcpu=ultrasparc")?
3. Do I need any special configure options, binutils versions, etc?  
4. Will Solaris 8 ld work for 3.0.3?

Please reply to <libstdc++@gcc.gnu.org>.

Nathan Myers
ncm at cantrip dot org