S390: Influence hwcaps/stfle via GLIBC_TUNABLES.

This patch enables the option to influence hwcaps and stfle bits used
by the s390 specific ifunc-resolvers.  The currently x86-specific
tunable glibc.cpu.hwcaps is also used on s390x to achieve the task. In
addition the user can also set a CPU arch-level like z13 instead of
single HWCAP and STFLE features.

Note that the tunable only handles the features which are really used
in the IFUNC-resolvers.  All others are ignored as the values are only
used inside glibc.  Thus we can influence:
- HWCAP_S390_VXRS (z13)
- HWCAP_S390_VXRS_EXT (z14)
- HWCAP_S390_VXRS_EXT2 (z15)
- STFLE_MIE3 (z15)

The influenced hwcap/stfle-bits are stored in the s390-specific
cpu_features struct which also contains reserved fields for future
usage.

The ifunc-resolvers and users of stfle bits are adjusted to use the
information from cpu_features struct.

On 31bit, the ELF_MACHINE_IRELATIVE macro is now also defined.
Otherwise the new ifunc-resolvers segfaults as they depend on
the not yet processed_rtld_global_ro@GLIBC_PRIVATE relocation.

1 files changed, 239 insertions, 0 deletions

diff --git a/sysdeps/s390/cpu-features.c b/sysdeps/s390/cpu-features.c
new file mode 100644
index 0000000000..afeb9b5638
--- /dev/null
+++ b/sysdeps/s390/cpu-features.c
@@ -0,0 +1,239 @@
+/* Initialize cpu feature data.  s390x version.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <cpu-features.h>
+
+#if HAVE_TUNABLES
+# include <elf/dl-tunables.h>
+# include <ifunc-memcmp.h>
+# include <string.h>
+extern __typeof (memcmp) MEMCMP_DEFAULT;
+#endif
+
+#if HAVE_TUNABLES
+# define S390_COPY_CPU_FEATURES(SRC_PTR, DEST_PTR)	\
+  (DEST_PTR)->hwcap = (SRC_PTR)->hwcap;			\
+  (DEST_PTR)->stfle_bits[0] = (SRC_PTR)->stfle_bits[0];
+
+static void
+TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
+{
+  /* The current IFUNC selection is always using the most recent
+     features which are available via AT_HWCAP or STFLE-bits.  But in
+     some scenarios it is useful to adjust this selection.
+
+     The environment variable:
+
+     GLIBC_TUNABLES=glibc.cpu.hwcaps=-xxx,yyy,zzz,....
+
+     can be used to enable HWCAP/STFLE feature yyy, disable HWCAP/STFLE feature
+     xxx, where the feature name is case-sensitive and has to match the ones
+     used below.  Furthermore, the ARCH-level zzz can be used to set various
+     HWCAP/STFLE features at once.  */
+
+  /* Copy the features from dl_s390_cpu_features, which contains the features
+     provided by AT_HWCAP and stfle-instruction.  */
+  struct cpu_features *cpu_features = &GLRO(dl_s390_cpu_features);
+  struct cpu_features cpu_features_orig;
+  S390_COPY_CPU_FEATURES (cpu_features, &cpu_features_orig);
+  struct cpu_features cpu_features_curr;
+  S390_COPY_CPU_FEATURES (cpu_features, &cpu_features_curr);
+
+  const char *token = valp->strval;
+  do
+    {
+      const char *token_end, *feature;
+      bool disable;
+      size_t token_len;
+      size_t feature_len;
+
+      /* Find token separator or end of string.  */
+      for (token_end = token; *token_end != ','; token_end++)
+	if (*token_end == '\0')
+	  break;
+
+      /* Determine feature.  */
+      token_len = token_end - token;
+      if (*token == '-')
+	{
+	  disable = true;
+	  feature = token + 1;
+	  feature_len = token_len - 1;
+	}
+      else
+	{
+	  disable = false;
+	  feature = token;
+	  feature_len = token_len;
+	}
+
+      /* Handle only the features here which are really used in the
+	 IFUNC-resolvers.  All others are ignored as the values are only used
+	 inside glibc.  */
+      bool reset_features = false;
+      unsigned long int hwcap_mask = 0UL;
+      unsigned long long stfle_bits0_mask = 0ULL;
+
+      if ((*feature == 'z' || *feature == 'a'))
+	{
+	  if ((feature_len == 5 && *feature == 'z'
+	       && MEMCMP_DEFAULT (feature, "zEC12", 5) == 0)
+	      || (feature_len == 6 && *feature == 'a'
+		  && MEMCMP_DEFAULT (feature, "arch10", 6) == 0))
+	    {
+	      reset_features = true;
+	      disable = true;
+	      hwcap_mask = HWCAP_S390_VXRS | HWCAP_S390_VXRS_EXT
+		| HWCAP_S390_VXRS_EXT2;
+	      stfle_bits0_mask = S390_STFLE_MASK_ARCH13_MIE3;
+	    }
+	  else if ((feature_len == 3 && *feature == 'z'
+		    && MEMCMP_DEFAULT (feature, "z13", 3) == 0)
+		   || (feature_len == 6 && *feature == 'a'
+		       && MEMCMP_DEFAULT (feature, "arch11", 6) == 0))
+	    {
+	      reset_features = true;
+	      disable = true;
+	      hwcap_mask = HWCAP_S390_VXRS_EXT | HWCAP_S390_VXRS_EXT2;
+	      stfle_bits0_mask = S390_STFLE_MASK_ARCH13_MIE3;
+	    }
+	  else if ((feature_len == 3 && *feature == 'z'
+		    && MEMCMP_DEFAULT (feature, "z14", 3) == 0)
+		   || (feature_len == 6 && *feature == 'a'
+		       && MEMCMP_DEFAULT (feature, "arch12", 6) == 0))
+	    {
+	      reset_features = true;
+	      disable = true;
+	      hwcap_mask = HWCAP_S390_VXRS_EXT2;
+	      stfle_bits0_mask = S390_STFLE_MASK_ARCH13_MIE3;
+	    }
+	  else if ((feature_len == 3 && *feature == 'z'
+		    && (MEMCMP_DEFAULT (feature, "z15", 3) == 0
+			|| MEMCMP_DEFAULT (feature, "z16", 3) == 0))
+		   || (feature_len == 6
+		       && (MEMCMP_DEFAULT (feature, "arch13", 6) == 0
+			   || MEMCMP_DEFAULT (feature, "arch14", 6) == 0)))
+	    {
+	      /* For z15 or newer we don't have to disable something,
+		 but we have to reset to the original values.  */
+	      reset_features = true;
+	    }
+	}
+      else if (*feature == 'H')
+	{
+	  if (feature_len == 15
+	      && MEMCMP_DEFAULT (feature, "HWCAP_S390_VXRS", 15) == 0)
+	    {
+	      hwcap_mask = HWCAP_S390_VXRS;
+	      if (disable)
+		hwcap_mask |= HWCAP_S390_VXRS_EXT | HWCAP_S390_VXRS_EXT2;
+	    }
+	  else if (feature_len == 19
+		   && MEMCMP_DEFAULT (feature, "HWCAP_S390_VXRS_EXT", 19) == 0)
+	    {
+	      hwcap_mask = HWCAP_S390_VXRS_EXT;
+	      if (disable)
+		hwcap_mask |= HWCAP_S390_VXRS_EXT2;
+	      else
+		hwcap_mask |= HWCAP_S390_VXRS;
+	    }
+	  else if (feature_len == 20
+		   && MEMCMP_DEFAULT (feature, "HWCAP_S390_VXRS_EXT2", 20) == 0)
+	    {
+	      hwcap_mask = HWCAP_S390_VXRS_EXT2;
+	      if (!disable)
+		hwcap_mask |= HWCAP_S390_VXRS | HWCAP_S390_VXRS_EXT;
+	    }
+	}
+      else if (*feature == 'S')
+	{
+	  if (feature_len == 10
+	      && MEMCMP_DEFAULT (feature, "STFLE_MIE3", 10) == 0)
+	    {
+	      stfle_bits0_mask = S390_STFLE_MASK_ARCH13_MIE3;
+	    }
+	}
+
+      /* Perform the actions determined above.  */
+      if (reset_features)
+	{
+	  S390_COPY_CPU_FEATURES (&cpu_features_orig, &cpu_features_curr);
+	}
+
+      if (hwcap_mask != 0UL)
+	{
+	  if (disable)
+	    cpu_features_curr.hwcap &= ~hwcap_mask;
+	  else
+	    cpu_features_curr.hwcap |= hwcap_mask;
+	}
+
+      if (stfle_bits0_mask != 0ULL)
+	{
+	  if (disable)
+	    cpu_features_curr.stfle_bits[0] &= ~stfle_bits0_mask;
+	  else
+	    cpu_features_curr.stfle_bits[0] |= stfle_bits0_mask;
+	}
+
+      /* Jump over current token ... */
+      token += token_len;
+
+      /* ... and skip token separator for next round.  */
+      if (*token == ',') token++;
+    }
+  while (*token != '\0');
+
+  /* Copy back the features after checking that no unsupported features were
+     enabled by user.  */
+  cpu_features->hwcap = cpu_features_curr.hwcap & cpu_features_orig.hwcap;
+  cpu_features->stfle_bits[0] = cpu_features_curr.stfle_bits[0]
+    & cpu_features_orig.stfle_bits[0];
+}
+#endif
+
+static inline void
+init_cpu_features (struct cpu_features *cpu_features)
+{
+  /* Fill cpu_features as passed by kernel and machine.  */
+  cpu_features->hwcap = GLRO(dl_hwcap);
+
+  /* We want just 1 double word to be returned.  */
+  if (__glibc_likely ((cpu_features->hwcap & HWCAP_S390_STFLE)
+		      && (cpu_features->hwcap & HWCAP_S390_ZARCH)
+		      && (cpu_features->hwcap & HWCAP_S390_HIGH_GPRS)))
+    {
+      register unsigned long reg0 __asm__("0") = 0;
+      __asm__ __volatile__(".machine push"        "\n\t"
+			   ".machine \"z9-109\""  "\n\t"
+			   ".machinemode \"zarch_nohighgprs\"\n\t"
+			   "stfle %0"             "\n\t"
+			   ".machine pop"         "\n"
+			   : "=QS" (cpu_features->stfle_bits[0]),
+			     "+d" (reg0)
+			   : : "cc");
+    }
+  else
+    {
+      cpu_features->stfle_bits[0] = 0ULL;
+    }
+
+#if HAVE_TUNABLES
+  TUNABLE_GET (glibc, cpu, hwcaps, tunable_val_t *, TUNABLE_CALLBACK (set_hwcaps));
+#endif
+}