[RFC 5/5] RISC-V: Expand PTHREAD_STACK_MIN to support RVV environment

[Vincent Chen <vincent.chen@sifive.com>]

In order to support all pthread operations in the RVV environment, here
PTHREAD_STACK_MIN is set to 4 times GLRO(dl_minsigstacksize), and the
default PTHREAD_STACK_MIN is expanded to 20K bytes.
---
 .../unix/sysv/linux/riscv/bits/pthread_stack_min.h | 21 ++++++++++++
 .../sysv/linux/riscv/sysconf-pthread_stack_min.h   | 39 ++++++++++++++++++++++
 2 files changed, 60 insertions(+)
 create mode 100644 sysdeps/unix/sysv/linux/riscv/bits/pthread_stack_min.h
 create mode 100644 sysdeps/unix/sysv/linux/riscv/sysconf-pthread_stack_min.h

diff --git a/sysdeps/unix/sysv/linux/riscv/bits/pthread_stack_min.h b/sysdeps/unix/sysv/linux/riscv/bits/pthread_stack_min.h
new file mode 100644
index 0000000..83585b3
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/bits/pthread_stack_min.h
@@ -0,0 +1,21 @@
+/* Definition of PTHREAD_STACK_MIN.  Linux/riscv version.
+   Copyright (C) 2021 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/>.  */
+
+/* Minimum size for a thread.  We are free to choose a reasonable value.  */
+#define PTHREAD_STACK_MIN	20480
diff --git a/sysdeps/unix/sysv/linux/riscv/sysconf-pthread_stack_min.h b/sysdeps/unix/sysv/linux/riscv/sysconf-pthread_stack_min.h
new file mode 100644
index 0000000..53ba6a1
--- /dev/null
+++ b/sysdeps/unix/sysv/linux/riscv/sysconf-pthread_stack_min.h
@@ -0,0 +1,39 @@
+/* __get_pthread_stack_min ().  Linux version.
+   Copyright (C) 2021 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/>.  */
+
+/* Return sysconf (_SC_THREAD_STACK_MIN).  */
+
+static inline long int
+__get_pthread_stack_min (void)
+{
+  /* sysconf (_SC_THREAD_STACK_MIN) >= sysconf (_SC_MINSIGSTKSZ).  */
+  long int pthread_stack_min = GLRO(dl_minsigstacksize) * 4;
+  assert (pthread_stack_min != 0);
+  _Static_assert (__builtin_constant_p (PTHREAD_STACK_MIN),
+		  "PTHREAD_STACK_MIN is constant");
+  /* Return MAX (PTHREAD_STACK_MIN, pthread_stack_min).  */
+  if (pthread_stack_min < PTHREAD_STACK_MIN)
+    pthread_stack_min = PTHREAD_STACK_MIN;
+  /* We have a private interface, __pthread_get_minstack@GLIBC_PRIVATE
+     which returns a larger size that includes the required TLS variable
+     space which has been determined at startup.  For sysconf here we are
+     conservative and don't include the space required for TLS access.
+     Eventually the TLS variable space will not be part of the stack
+     (Bug 11787).  */
+  return pthread_stack_min;
+}
-- 
2.7.4