riscv: Add Linux hwprobe syscall support

Add awareness and a thin wrapper function around a new Linux system call
that allows callers to get architecture and microarchitecture
information about the CPUs from the kernel. This can be used to
do things like dynamically choose a memcpy implementation.

Signed-off-by: Evan Green <evan@rivosinc.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

6 files changed, 125 insertions, 2 deletions

diff --git a/sysdeps/unix/sysv/linux/riscv/Makefile b/sysdeps/unix/sysv/linux/riscv/Makefile
index 4b6eacb..04abf22 100644
--- a/sysdeps/unix/sysv/linux/riscv/Makefile
+++ b/sysdeps/unix/sysv/linux/riscv/Makefile
@@ -1,6 +1,14 @@
 ifeq ($(subdir),misc)
-sysdep_headers += sys/cachectl.h
-sysdep_routines += flush-icache
+sysdep_headers += \
+  sys/cachectl.h \
+  sys/hwprobe.h \
+  # sysdep_headers
+
+sysdep_routines += \
+  flush-icache \
+  hwprobe \
+  # sysdep_routines
+
 endif
 
 ifeq ($(subdir),stdlib)
diff --git a/sysdeps/unix/sysv/linux/riscv/Versions b/sysdeps/unix/sysv/linux/riscv/Versions
index 5625d2a..8183e9f 100644
--- a/sysdeps/unix/sysv/linux/riscv/Versions
+++ b/sysdeps/unix/sysv/linux/riscv/Versions
@@ -8,4 +8,7 @@ libc {
   GLIBC_2.27 {
     __riscv_flush_icache;
   }
+  GLIBC_2.40 {
+    __riscv_hwprobe;
+  }
 }
diff --git a/sysdeps/unix/sysv/linux/riscv/hwprobe.c b/sysdeps/unix/sysv/linux/riscv/hwprobe.c
new file mode 100644
index 0000000..28a4481
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/hwprobe.c
@@ -0,0 +1,36 @@
+/* RISC-V hardware feature probing support on Linux
+   Copyright (C) 2024 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 <sys/syscall.h>
+#include <sys/hwprobe.h>
+#include <sysdep.h>
+#include <sysdep-vdso.h>
+
+int __riscv_hwprobe (struct riscv_hwprobe *pairs, size_t pair_count,
+		     size_t cpu_count, unsigned long int *cpus,
+		     unsigned int flags)
+{
+  int r;
+
+  r = INTERNAL_SYSCALL_CALL (riscv_hwprobe, pairs, pair_count,
+                             cpu_count, cpus, flags);
+
+  /* Negate negative errno values to match pthreads API. */
+  return -r;
+}
diff --git a/sysdeps/unix/sysv/linux/riscv/rv32/libc.abilist b/sysdeps/unix/sysv/linux/riscv/rv32/libc.abilist
index f90c94b..6397a9c 100644
--- a/sysdeps/unix/sysv/linux/riscv/rv32/libc.abilist
+++ b/sysdeps/unix/sysv/linux/riscv/rv32/libc.abilist
@@ -2511,3 +2511,4 @@ GLIBC_2.39 stdc_trailing_zeros_ui F
 GLIBC_2.39 stdc_trailing_zeros_ul F
 GLIBC_2.39 stdc_trailing_zeros_ull F
 GLIBC_2.39 stdc_trailing_zeros_us F
+GLIBC_2.40 __riscv_hwprobe F
diff --git a/sysdeps/unix/sysv/linux/riscv/rv64/libc.abilist b/sysdeps/unix/sysv/linux/riscv/rv64/libc.abilist
index e04ff93..71bbf94 100644
--- a/sysdeps/unix/sysv/linux/riscv/rv64/libc.abilist
+++ b/sysdeps/unix/sysv/linux/riscv/rv64/libc.abilist
@@ -2711,3 +2711,4 @@ GLIBC_2.39 stdc_trailing_zeros_ui F
 GLIBC_2.39 stdc_trailing_zeros_ul F
 GLIBC_2.39 stdc_trailing_zeros_ull F
 GLIBC_2.39 stdc_trailing_zeros_us F
+GLIBC_2.40 __riscv_hwprobe F
diff --git a/sysdeps/unix/sysv/linux/riscv/sys/hwprobe.h b/sysdeps/unix/sysv/linux/riscv/sys/hwprobe.h
new file mode 100644
index 0000000..5592b9e
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/sys/hwprobe.h
@@ -0,0 +1,74 @@
+/* RISC-V architecture probe interface
+   Copyright (C) 2024 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 _SYS_HWPROBE_H
+#define _SYS_HWPROBE_H 1
+
+#include <features.h>
+#include <stddef.h>
+#ifdef __has_include
+# if __has_include (<asm/hwprobe.h>)
+#  include <asm/hwprobe.h>
+# endif
+#endif
+
+/* Define a (probably stale) version of the interface if the Linux headers
+   aren't present.  */
+#ifndef RISCV_HWPROBE_KEY_MVENDORID
+struct riscv_hwprobe {
+	signed long long int key;
+	unsigned long long int value;
+};
+
+#define RISCV_HWPROBE_KEY_MVENDORID 0
+#define RISCV_HWPROBE_KEY_MARCHID 1
+#define RISCV_HWPROBE_KEY_MIMPID 2
+#define RISCV_HWPROBE_KEY_BASE_BEHAVIOR 3
+#define  RISCV_HWPROBE_BASE_BEHAVIOR_IMA (1 << 0)
+#define RISCV_HWPROBE_KEY_IMA_EXT_0 4
+#define  RISCV_HWPROBE_IMA_FD (1 << 0)
+#define  RISCV_HWPROBE_IMA_C (1 << 1)
+#define  RISCV_HWPROBE_IMA_V (1 << 2)
+#define  RISCV_HWPROBE_EXT_ZBA (1 << 3)
+#define  RISCV_HWPROBE_EXT_ZBB (1 << 4)
+#define  RISCV_HWPROBE_EXT_ZBS (1 << 5)
+#define  RISCV_HWPROBE_EXT_ZICBOZ (1 << 6)
+#define RISCV_HWPROBE_KEY_CPUPERF_0 5
+#define  RISCV_HWPROBE_MISALIGNED_UNKNOWN (0 << 0)
+#define  RISCV_HWPROBE_MISALIGNED_EMULATED (1 << 0)
+#define  RISCV_HWPROBE_MISALIGNED_SLOW (2 << 0)
+#define  RISCV_HWPROBE_MISALIGNED_FAST (3 << 0)
+#define  RISCV_HWPROBE_MISALIGNED_UNSUPPORTED (4 << 0)
+#define  RISCV_HWPROBE_MISALIGNED_MASK (7 << 0)
+#define RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE 6
+
+#endif /* RISCV_HWPROBE_KEY_MVENDORID */
+
+__BEGIN_DECLS
+
+extern int __riscv_hwprobe (struct riscv_hwprobe *__pairs, size_t __pair_count,
+			    size_t __cpu_count, unsigned long int *__cpus,
+			    unsigned int __flags)
+     __nonnull ((1)) __wur
+     __fortified_attr_access (__read_write__, 1, 2)
+     __fortified_attr_access (__read_only__, 4, 3);
+
+__END_DECLS
+
+#endif /* sys/hwprobe.h */