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, 25 insertions, 0 deletions

diff --git a/sysdeps/s390/dl-tunables.list b/sysdeps/s390/dl-tunables.list
new file mode 100644
index 0000000..7a09828
--- /dev/null
+++ b/sysdeps/s390/dl-tunables.list
@@ -0,0 +1,25 @@
+# s390 specific tunables.
+# 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/>.
+
+glibc {
+  cpu {
+    hwcaps {
+      type: STRING
+    }
+  }
+}