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* [2.26 COMMITTED] x86: Fix Haswell CPU string flags (BZ#23709)
@ 2018-01-01  0:00 Florian Weimer
  0 siblings, 0 replies; only message in thread
From: Florian Weimer @ 2018-01-01  0:00 UTC (permalink / raw)
  To: libc-stable

From: Adhemerval Zanella <>

Th commit 'Disable TSX on some Haswell processors.' (2702856bf4) changed the
default flags for Haswell models.  Previously, new models were handled by the
default switch path, which assumed a Core i3/i5/i7 if AVX is available. After
the patch, Haswell models (0x3f, 0x3c, 0x45, 0x46) do not set the flags
Fast_Rep_String, Fast_Unaligned_Load, Fast_Unaligned_Copy, and
Prefer_PMINUB_for_stringop (only the TSX one).

This patch fixes it by disentangle the TSX flag handling from the memory
optimization ones.  The strstr case cited on patch now selects the
__strstr_sse2_unaligned as expected for the Haswell cpu.

Checked on x86_64-linux-gnu.

	[BZ #23709]
	* sysdeps/x86/cpu-features.c (init_cpu_features): Set TSX bits
	independently of other flags.

(cherry picked from commit c3d8dc45c9df199b8334599a6cbd98c9950dba62)

2018-10-23  Adhemerval Zanella  <>

	[BZ #23709]
	* sysdeps/x86/cpu-features.c (init_cpu_features): Set TSX bits
	independently of other flags.

diff --git a/NEWS b/NEWS
index f6c9a1412c..d99732fe06 100644
--- a/NEWS
+++ b/NEWS
@@ -156,6 +156,7 @@ The following bugs are resolved with this release:
   [23459] COMMON_CPUID_INDEX_80000001 isn't populated for Intel processors
   [23562] signal: Use correct type for si_band in siginfo_t
   [23579] libc: Errors misreported in preadv2
+  [23709] Fix CPU string flags for Haswell-type CPUs
 Version 2.26
diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c
index a66d468b20..b3a5f4b26a 100644
--- a/sysdeps/x86/cpu-features.c
+++ b/sysdeps/x86/cpu-features.c
@@ -297,7 +297,13 @@ init_cpu_features (struct cpu_features *cpu_features)
 		    | bit_arch_Fast_Unaligned_Copy
 		    | bit_arch_Prefer_PMINUB_for_stringop);
+	    }
+	 /* Disable TSX on some Haswell processors to avoid TSX on kernels that
+	    weren't updated with the latest microcode package (which disables
+	    broken feature by default).  */
+	 switch (model)
+	    {
 	    case 0x3f:
 	      /* Xeon E7 v3 with stepping >= 4 has working TSX.  */
 	      if (stepping >= 4)

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2018-01-01  0:00 [2.26 COMMITTED] x86: Fix Haswell CPU string flags (BZ#23709) Florian Weimer

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