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Re: thread-ready ABIs


On Mon, Jan 21, 2002 at 10:52:53AM -0800, H . J . Lu wrote:
> On Mon, Jan 21, 2002 at 10:36:26AM -0800, Ulrich Drepper wrote:
> > "H . J . Lu" <hjl@lucon.org> writes:
> > 
> > > Ulrich, should applciations have access to thread register directly?
> > 
> > It doesn't matter.  The value isn't changed in the lifetime of a
> > thread.  So the overhead of a syscall wouldn't be too much.  And
> > protection against programs overwriting the register isn't necessary.
> > It's the program's fault if that happens.
> 
> Thq question is if we should reserve $23 outside of glibc. $23 is
> a saved register in the MIPS ABI. It doesn't change across function
> calls. If applications outside of glibc don't need to access the
> thread register directly, that means $23 can be used as a saved
> register. We don't have to change anything when compiling applications.
> We only need to compile glibc with $23 reserved as the thread register.

That's not right.  If it is call-saved in the application, that means
the application can use it.  Main may have to restore it before it
returns to __libc_start_main, but that doesn't do you any good.

It doesn't change across function calls, but it does change inside
function calls.

-- 
Daniel Jacobowitz                           Carnegie Mellon University
MontaVista Software                         Debian GNU/Linux Developer


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