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

[H. Peter Anvin]

On May 26, 2026 5:29:25 PM PDT, "Maciej W. Rozycki" <macro@xxxxxxxxxxx> wrote:
>On Tue, 26 May 2026, H. Peter Anvin wrote:
>
>> > 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.
>> 
>> However, x87 should be testable on any x86 silicon.
>
> We have model-dependent quirks, clearly.  Actually even this system is 
>not pure x87 anymore as it has the MMX extension, and with the recent 
>removal of i486 support it's getting harder and harder to get at the right 
>environment.  As we spoke IIRC last year, I'll try to maintain support for 
>the i486 with emulation off-tree.  The hard part might be RDTSC.
>
> And I've seen cases of code relying on newer hardware features by chance, 
>which then eventually broke when tried on original hardware.  I've seen 
>and fixed QEMU bugs too where ISA subsetting wasn't correct and software 
>that worked on QEMU broke on real hw.
>
> Then haven't more recent x86 architecture revisions switched away from 
>the venerable x87 FPU and its data formats for FP computations?  A genuine 
>question as I have not been following progress here.  What I know though 
>is the x87 stack architecture is antiquated, and hard to pipeline and emit 
>optimised code for.  And also mixing computations of various precisions is 
>problematic.
>
>  Maciej

SSE/AVX is preferred, but x87 is still supported. It is certainly less performant though.