Re: strange message appearing in a fresh current

On Sat, 19 Jun 2004, Divacky Roman wrote:

> > > built for i686 cpu (amd duron) with -O -pipe
> >
> > Hmm.  Don't Durons have FXSR?  (I686_CPU or CPU_ENABLE_SSE) and not
> > CPU_DISABLE_SSE together with a CPU that supports FXSR should give
> > a configuration that is not affected by the bug.
>
>   Origin = "AuthenticAMD"  Id = 0x631  Stepping = 1
>     Features=0x183f9ff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,MMX,FXSR>
>       AMD Features=0xc0440000<RSVD,AMIE,DSP,3DNow!>
>
> I just set
> cpu             I686_CPU
>
> no CPU_* at all. And the bug is there...

Ah.  It needs SSE in the cpuid too, and your Duron doesn't have it.  I
think Athlons got SSE starting with the XP.

The configuration of this is confusing.  From i386/initcpu.c:

% #if !defined(CPU_ENABLE_SSE) && defined(I686_CPU)
% #define CPU_ENABLE_SSE
% #endif
% #if defined(CPU_DISABLE_SSE)
% #undef CPU_ENABLE_SSE
% #endif

So I686_CPU gives CPU_ENABLE_SSE unless you use CPU_DISABLE_SSE.

% /*
%  * Initialize CR4 (Control register 4) to enable SSE instructions.
%  */
% void
% enable_sse(void)
% {
% #if defined(CPU_ENABLE_SSE)
% 	if ((cpu_feature & CPUID_XMM) && (cpu_feature & CPUID_FXSR)) {
% 		load_cr4(rcr4() | CR4_FXSR | CR4_XMM);
% 		cpu_fxsr = hw_instruction_sse = 1;
% 	}
% #endif
% }

Here CPUID_XMM is a confusing alias for CPUID_SSE (the identifcation message
only prints "SSE").  So to get cpu_fxsr, you need CPU_ENABLE_SSE or
I686_CPU && !CPU_DISABLE_SSE in the FreeBSD config, and SSE and FXSR in
the hardware.

% 		} else if (strcmp(cpu_vendor, "AuthenticAMD") == 0) {
% #if defined(I686_CPU) && defined(CPU_ATHLON_SSE_HACK)
% 			/*
% 			 * Sometimes the BIOS doesn't enable SSE instructions.
% 			 * According to AMD document 20734, the mobile
% 			 * Duron, the (mobile) Athlon 4 and the Athlon MP
% 			 * support SSE. These correspond to cpu_id 0x66X
% 			 * or 0x67X.
% 			 */
% 			if ((cpu_feature & CPUID_XMM) == 0 &&
% 			    ((cpu_id & ~0xf) == 0x660 ||
% 			     (cpu_id & ~0xf) == 0x670 ||
% 			     (cpu_id & ~0xf) == 0x680)) {
% 				u_int regs[4];
% 				wrmsr(0xC0010015, rdmsr(0xC0010015) & ~0x08000);
% 				do_cpuid(1, regs);
% 				cpu_feature = regs[3];
% 			}
% #endif

And for broken BIOSes, CPU_ATHLON_SSE_HACK is also needed to get SSE.

Bruce