Re: [PATCH v2 2/3] x86/cpu/intel: Simplify F00F bug notice using pr_notice_once()

[David Laight]

On Tue, 26 May 2026 13:49:08 -0700
"H. Peter Anvin" <hpa@xxxxxxxxx> wrote:

> On May 26, 2026 12:15:19 PM PDT, "Maciej W. Rozycki" <macro@xxxxxxxxxxx> wrote:
> >On Tue, 26 May 2026, Christian Ludloff wrote:
> >  
> >> > > > This actually continues getting serious use, most recently for glibc ISO
> >> > > > C formatted input/output test coverage improvement and the x87 FP formats.  
> >> 
> >> x87 testing... on a Pentium?  
> >
> > Yes, 32-bit x86 remains a supported target with the GNU C library, down 
> >to i486 I believe, that includes dedicated platform code such as for the 
> >80-bit extended format, so this was a good portability exercise, given 
> >that the scope of the tests were floating-point formatted input/output 
> >specifiers, not previously sufficiently covered.
> >
> >  Maciej  
> 
> However, x87 should be testable on any x86 silicon.

And gets used for 'long double' on x86-64.

If full precision is enabled there are a whole lot of horrid corner cases.
Mostly due to correctly generating the FP signals when the 80bit return
value from a function is written to a 64bit 'double'.

-- David