[RFC,04/19] riscv: Add hart feature run-time detection framework

diff --git a/sysdeps/riscv/dl-machine.h b/sysdeps/riscv/dl-machine.h
index c0c9bd93ad..43f4f96c0e 100644
--- a/sysdeps/riscv/dl-machine.h
+++ b/sysdeps/riscv/dl-machine.h
@@ -28,6 +28,7 @@ 
 #include <dl-irel.h>
 #include <dl-static-tls.h>
 #include <dl-machine-rel.h>
+#include <hart-features.c>
 
 #ifndef _RTLD_PROLOGUE
 # define _RTLD_PROLOGUE(entry)						\
@@ -148,6 +149,18 @@  elf_machine_fixup_plt (struct link_map *map, lookup_t t,
   return *reloc_addr = value;
 }
 
+#define DL_PLATFORM_INIT dl_platform_init ()
+
+static inline void __attribute__ ((unused))
+dl_platform_init (void)
+{
+#ifdef SHARED
+  /* init_hart_features has been called early from __libc_start_main in
+     static executable.  */
+  init_hart_features (&GLRO(dl_riscv_hart_features));
+#endif /* SHARED */
+}
+
 #endif /* !dl_machine_h */
 
 #ifdef RESOLVE_MAP
diff --git a/sysdeps/riscv/ldsodefs.h b/sysdeps/riscv/ldsodefs.h
index 90e95e60c5..4b184de255 100644
--- a/sysdeps/riscv/ldsodefs.h
+++ b/sysdeps/riscv/ldsodefs.h
@@ -20,6 +20,7 @@ 
 #define _RISCV_LDSODEFS_H 1
 
 #include <elf.h>
+#include <hart-features.h>
 
 struct La_riscv_regs;
 struct La_riscv_retval;
diff --git a/sysdeps/unix/sysv/linux/riscv/dl-procinfo.c b/sysdeps/unix/sysv/linux/riscv/dl-procinfo.c
new file mode 100644
index 0000000000..ce137d10c4
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/dl-procinfo.c
@@ -0,0 +1,62 @@ 
+/* Data for RISC-V version of processor capability information.
+   Copyright (C) 2022 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/>.  */
+
+/* This information must be kept in sync with the _DL_PLATFORM_COUNT
+   definitions in procinfo.h.
+
+   If anything should be added here check whether the size of each string
+   is still ok with the given array size.
+
+   All the #ifdefs in the definitions are quite irritating but
+   necessary if we want to avoid duplicating the information.  There
+   are three different modes:
+
+   - PROCINFO_DECL is defined.  This means we are only interested in
+     declarations.
+
+   - PROCINFO_DECL is not defined:
+
+     + if SHARED is defined the file is included in an array
+       initializer.  The .element = { ... } syntax is needed.
+
+     + if SHARED is not defined a normal array initialization is
+       needed.
+  */
+
+#ifndef PROCINFO_CLASS
+# define PROCINFO_CLASS
+#endif
+
+#if !IS_IN (ldconfig)
+# if !defined PROCINFO_DECL && defined SHARED
+  ._dl_riscv_hart_features
+# else
+PROCINFO_CLASS struct hart_features _dl_riscv_hart_features
+# endif
+# ifndef PROCINFO_DECL
+= { }
+# endif
+# if !defined SHARED || defined PROCINFO_DECL
+;
+# else
+,
+# endif
+#endif
+
+#undef PROCINFO_DECL
+#undef PROCINFO_CLASS
diff --git a/sysdeps/unix/sysv/linux/riscv/dl-procinfo.h b/sysdeps/unix/sysv/linux/riscv/dl-procinfo.h
new file mode 100644
index 0000000000..27aaebe02d
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/dl-procinfo.h
@@ -0,0 +1,46 @@ 
+/* RISC-V version of processor capability information handling macros.
+   Copyright (C) 2022 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/>.  */
+
+#ifndef _DL_PROCINFO_H
+#define _DL_PROCINFO_H	1
+
+#include <sys/auxv.h>
+#include <unistd.h>
+#include <ldsodefs.h>
+#include <sysdep.h>
+
+/* We cannot provide a general printing function.  */
+#define _dl_procinfo(word, val) -1
+
+/* There are no hardware capabilities defined.  */
+#define _dl_hwcap_string(idx) ""
+
+/* By default there is no important hardware capability.  */
+#define HWCAP_IMPORTANT (0)
+
+/* We don't have any hardware capabilities.  */
+#define _DL_HWCAP_COUNT	0
+
+#define _dl_string_hwcap(str) (-1)
+
+/* There're no platforms to filter out.  */
+#define _DL_HWCAP_PLATFORM 0
+
+#define _dl_string_platform(str) (-1)
+
+#endif /* dl-procinfo.h */
diff --git a/sysdeps/unix/sysv/linux/riscv/hart-features.c b/sysdeps/unix/sysv/linux/riscv/hart-features.c
new file mode 100644
index 0000000000..41111eff57
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/hart-features.c
@@ -0,0 +1,43 @@ 
+/* Initialize hart feature data.  RISC-V version.
+   This file is part of the GNU C Library.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+
+   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 <hart-features.h>
+
+/* The code in this file is executed very early, so we cannot call
+   indirect functions because ifunc support is not initialized.
+   Therefore this file adds a few simple helper functions to avoid
+   dependencies to functions outside of this file.  */
+
+static inline void
+inhibit_loop_to_libcall
+simple_memset (void *s, int c, size_t n)
+{
+  char *p = (char*)s;
+  while (n != 0)
+    {
+      *p = c;
+      n--;
+    }
+}
+
+/* Discover hart features and store them.  */
+static inline void
+init_hart_features (struct hart_features *hart_features)
+{
+  simple_memset (hart_features, 0, sizeof (*hart_features));
+}
diff --git a/sysdeps/unix/sysv/linux/riscv/hart-features.h b/sysdeps/unix/sysv/linux/riscv/hart-features.h
new file mode 100644
index 0000000000..a417cbc326
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/hart-features.h
@@ -0,0 +1,26 @@ 
+/* Initialize CPU feature data.  RISC-V version.
+   This file is part of the GNU C Library.
+   Copyright (C) 2022 Free Software Foundation, Inc.
+
+   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/>.  */
+
+#ifndef _CPU_FEATURES_RISCV_H
+#define _CPU_FEATURES_RISCV_H
+
+struct hart_features
+{
+};
+
+#endif /* _CPU_FEATURES_RISCV_H  */
diff --git a/sysdeps/unix/sysv/linux/riscv/libc-start.c b/sysdeps/unix/sysv/linux/riscv/libc-start.c
new file mode 100644
index 0000000000..57c7c09223
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/libc-start.c
@@ -0,0 +1,29 @@ 
+/* Override csu/libc-start.c on RISC-V
+   Copyright (C) 2022 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/>.  */
+
+#ifndef SHARED
+
+# include <ldsodefs.h>
+# include <hart-features.c>
+
+extern struct hart_features _dl_riscv_hart_features;
+
+# define ARCH_INIT_CPU_FEATURES() init_hart_features (&_dl_riscv_hart_features)
+
+#endif
+#include <csu/libc-start.c>