svn commit: r322345 - stable/11/lib/libc/x86/sys

[Andre Albsmeier]

On Thu, 10-Aug-2017 at 09:00:15 +0000, Konstantin Belousov wrote:
> Author: kib
> Date: Thu Aug 10 09:00:15 2017
> New Revision: 322345
> URL: https://svnweb.freebsd.org/changeset/base/322345
> 
> Log:
>   MFC r321608:
>   Use MFENCE to serialize RDTSC on non-Intel CPUs.

This broke libc on my

FreeBSD clang version 4.0.0 (tags/RELEASE_400/final 297347) (based on LLVM 4.0.0)
VT(vga): text 80x25
CPU: AMD-K6tm w/ multimedia extensions (199.44-MHz 586-class CPU)
  Origin="AuthenticAMD"  Id=0x562  Family=0x5  Model=0x6  Stepping=2
  Features=0x8001bf<FPU,VME,DE,PSE,TSC,MSR,MCE,CX8,MMX>
  AMD Features=0x400<<b10>>

On system start, it actually makes various programmes hang until
Ctrl-C is pressed. Reboot is not possible (endlessly hanging with
'zillions of defunct processes).

Going back to r322042 fixes it...

        -Andre

> 
> Modified:
>   stable/11/lib/libc/x86/sys/__vdso_gettc.c
> Directory Properties:
>   stable/11/   (props changed)
> 
> Modified: stable/11/lib/libc/x86/sys/__vdso_gettc.c
> ==============================================================================
> --- stable/11/lib/libc/x86/sys/__vdso_gettc.c	Thu Aug 10 06:59:43 2017	(r322344)
> +++ stable/11/lib/libc/x86/sys/__vdso_gettc.c	Thu Aug 10 09:00:15 2017	(r322345)
> @@ -52,57 +52,108 @@ __FBSDID("$FreeBSD$");
>  #endif
>  #include "libc_private.h"
>  
> +static enum LMB {
> +	LMB_UNKNOWN,
> +	LMB_NONE,
> +	LMB_MFENCE,
> +	LMB_LFENCE
> +} lfence_works = LMB_UNKNOWN;
> +
>  static void
> -lfence_mb(void)
> +cpuidp(u_int leaf, u_int p[4])
>  {
> +
> +	__asm __volatile(
>  #if defined(__i386__)
> -	static int lfence_works = -1;
> +	    "	pushl	%%ebx\n"
> +#endif
> +	    "	cpuid\n"
> +#if defined(__i386__)
> +	    "	movl	%%ebx,%1\n"
> +	    "	popl	%%ebx"
> +#endif
> +	    : "=a" (p[0]),
> +#if defined(__i386__)
> +	    "=r" (p[1]),
> +#elif defined(__amd64__)
> +	    "=b" (p[1]),
> +#else
> +#error "Arch"
> +#endif
> +	    "=c" (p[2]), "=d" (p[3])
> +	    :  "0" (leaf));
> +}
> +
> +static enum LMB
> +select_lmb(void)
> +{
> +	u_int p[4];
> +	static const char intel_id[] = "GenuntelineI";
> +
> +	cpuidp(0, p);
> +	return (memcmp(p + 1, intel_id, sizeof(intel_id) - 1) == 0 ?
> +	    LMB_LFENCE : LMB_MFENCE);
> +}
> +
> +static void
> +init_fence(void)
> +{
> +#if defined(__i386__)
>  	u_int cpuid_supported, p[4];
>  
> -	if (lfence_works == -1) {
> -		__asm __volatile(
> -		    "	pushfl\n"
> -		    "	popl	%%eax\n"
> -		    "	movl    %%eax,%%ecx\n"
> -		    "	xorl    $0x200000,%%eax\n"
> -		    "	pushl	%%eax\n"
> -		    "	popfl\n"
> -		    "	pushfl\n"
> -		    "	popl    %%eax\n"
> -		    "	xorl    %%eax,%%ecx\n"
> -		    "	je	1f\n"
> -		    "	movl	$1,%0\n"
> -		    "	jmp	2f\n"
> -		    "1:	movl	$0,%0\n"
> -		    "2:\n"
> -		    : "=r" (cpuid_supported) : : "eax", "ecx", "cc");
> -		if (cpuid_supported) {
> -			__asm __volatile(
> -			    "	pushl	%%ebx\n"
> -			    "	cpuid\n"
> -			    "	movl	%%ebx,%1\n"
> -			    "	popl	%%ebx\n"
> -			    : "=a" (p[0]), "=r" (p[1]), "=c" (p[2]), "=d" (p[3])
> -			    :  "0" (0x1));
> -			lfence_works = (p[3] & CPUID_SSE2) != 0;
> -		} else
> -			lfence_works = 0;
> -	}
> -	if (lfence_works == 1)
> -		lfence();
> +	__asm __volatile(
> +	    "	pushfl\n"
> +	    "	popl	%%eax\n"
> +	    "	movl    %%eax,%%ecx\n"
> +	    "	xorl    $0x200000,%%eax\n"
> +	    "	pushl	%%eax\n"
> +	    "	popfl\n"
> +	    "	pushfl\n"
> +	    "	popl    %%eax\n"
> +	    "	xorl    %%eax,%%ecx\n"
> +	    "	je	1f\n"
> +	    "	movl	$1,%0\n"
> +	    "	jmp	2f\n"
> +	    "1:	movl	$0,%0\n"
> +	    "2:\n"
> +	    : "=r" (cpuid_supported) : : "eax", "ecx", "cc");
> +	if (cpuid_supported) {
> +		cpuidp(0x1, p);
> +		if ((p[3] & CPUID_SSE2) != 0)
> +			lfence_works = select_lmb();
> +	} else
> +		lfence_works = LMB_NONE;
>  #elif defined(__amd64__)
> -	lfence();
> +	lfence_works = select_lmb();
>  #else
> -#error "arch"
> +#error "Arch"
>  #endif
>  }
>  
> +static void
> +rdtsc_mb(void)
> +{
> +
> +again:
> +	if (__predict_true(lfence_works == LMB_LFENCE)) {
> +		lfence();
> +		return;
> +	} else if (lfence_works == LMB_MFENCE) {
> +		mfence();
> +		return;
> +	} else if (lfence_works == LMB_NONE) {
> +		return;
> +	}
> +	init_fence();
> +	goto again;
> +}
> +
>  static u_int
>  __vdso_gettc_rdtsc_low(const struct vdso_timehands *th)
>  {
>  	u_int rv;
>  
> -	lfence_mb();
> +	rdtsc_mb();
>  	__asm __volatile("rdtsc; shrd %%cl, %%edx, %0"
>  	    : "=a" (rv) : "c" (th->th_x86_shift) : "edx");
>  	return (rv);
> @@ -112,7 +163,7 @@ static u_int
>  __vdso_rdtsc32(void)
>  {
>  
> -	lfence_mb();
> +	rdtsc_mb();
>  	return (rdtsc32());
>  }
>  
> @@ -211,7 +262,7 @@ __vdso_hyperv_tsc(struct hyperv_reftsc *tsc_ref, u_int
>  		scale = tsc_ref->tsc_scale;
>  		ofs = tsc_ref->tsc_ofs;
>  
> -		lfence_mb();
> +		rdtsc_mb();
>  		tsc = rdtsc();
>  
>  		/* ret = ((tsc * scale) >> 64) + ofs */
> _______________________________________________
> svn-src-stable-11 at freebsd.org mailing list
> https://lists.freebsd.org/mailman/listinfo/svn-src-stable-11
> To unsubscribe, send any mail to "svn-src-stable-11-unsubscribe at freebsd.org"

-- 
Stuxnet? Find ich gut. Manche lernen nur auf die harte Tour...