critical floating point incompatibility

[John Baldwin]

On Wednesday 28 January 2009 2:24:21 pm Bakul Shah wrote:
> On Mon, 26 Jan 2009 16:51:28 EST John Baldwin <jhb at freebsd.org>  wrote:
> > On Friday 21 December 2007 3:16:33 pm Kostik Belousov wrote:
> > > On Fri, Dec 21, 2007 at 10:11:24AM -0800, Bakul Shah wrote:
> > > > Peter Jeremy <peterjeremy at optushome.com.au> wrote:
> > > > > On Wed, Dec 19, 2007 at 09:40:34PM -0800, Carl Shapiro wrote:
> > > > > >The default setting of the x87 floating point control word on the 
i386
> > > > > >port is 0x127F.  Among other things, this value sets the precision
> > > > > >control to double precision.  The default setting of the x87 
floating
> > > > > >point control word on the AMD64 is 0x37F.
> > > > > ...
> > > > > >It seems clear that the right thing to do is to set the floating 
point
> > > > > >environment to the i386 default for i386 binaries.  Is the current
> > > > > >behavior intended?
> > > > > 
> > > > > I believe this is an oversight.  See the thread beginning
> > > > > 
> > 
http://lists.freebsd.org/pipermail/freebsd-stable/2007-November/037947.html
> > > > 
> > > > >From reading Bruce's last message in that thread, seems to me
> > > > may be default for 64bit binaries should be the same as on
> > > > i386. Anyone wanting different behavior can always call
> > > > fpsetprec() etc.
> > > > 
> > > > I think the fix is to change __INITIAL_FPUCW__ in
> > > > /sys/amd64/include/fpu.h to 0x127F like on i386.
> > > I think this shall be done for 32-bit processes only, or we get into
> > > another ABI breaking nightmare.
> > 
> > How about something like this:  (Carl, can you please test this?)
> 
> Your patch works fine on a recent -current.  Here is a
> program Carl had sent me more than a year ago for testing
> this.  May be some varition of it can be added to
> compatibility tests.
> 
> #include <stdio.h>
> int main(void)
> {
>      unsigned short cw;
>      __asm__ __volatile__ ("fnstcw %0":"=m"(*&cw));
>      printf("cw=%#x\n", cw);
>      return 0;
> }
> 
> -- bakul

Cool, thanks for testing!

-- 
John Baldwin