Implement sysconf for Arm

- add support for using sysconf to get page size in _mallocr.c via
  HAVE_SYSCONF_PAGESIZE flag set in configure.host
- set flag in configure.host for arm and add a default sysconf implementation
  in libc/sys/arm that returns the page size
- the default implementation can be overridden outside newlib to allow a
  different page size to improve malloc on devices with a small footprint
  without needing to rebuild newlib
- this patch is based on a contribution from Torbjorn Svensson and
  Niklas Dahlquist (https://ecos.sourceware.org/ml/newlib/current/017616.html)

newlib/configure.host

@@ -628,6 +628,7 @@ newlib_cflags="${newlib_cflags} -DCLOCK_PROVIDED -DMALLOC_PROVIDED -DEXIT_PROVID
 	;;
   arm*-*-pe)
 	syscall_dir=syscalls
+	newlib_cflags="${newlib_cflags} -DHAVE_SYSCONF_PAGESIZE"
 	;;
   arm*-*-*)
 	syscall_dir=syscalls
@@ -642,6 +643,7 @@ newlib_cflags="${newlib_cflags} -DCLOCK_PROVIDED -DMALLOC_PROVIDED -DEXIT_PROVID
 #         newlib_cflags="${newlib_cflags} -DARM_RDP_MONITOR"
 	  newlib_cflags="${newlib_cflags} -DARM_RDI_MONITOR"
 	fi
+	newlib_cflags="${newlib_cflags} -DHAVE_SYSCONF_PAGESIZE"
 	;;
   avr*)
 	newlib_cflags="${newlib_cflags} -DNO_EXEC -DSMALL_MEMORY -DMISSING_SYSCALL_NAMES"

newlib/libc/stdlib/_mallocr.c

@@ -320,12 +320,14 @@ extern "C" {
 #endif
 
 #ifndef _WIN32
+#ifndef HAVE_SYSCONF_PAGESIZE
 #ifdef SMALL_MEMORY
 #define malloc_getpagesize (128)
 #else
 #define malloc_getpagesize (4096)
 #endif
 #endif
+#endif
 
 #if __STD_C
 extern void __malloc_lock(struct _reent *);

newlib/libc/sys/arm/Makefile.inc

@@ -1,6 +1,6 @@
 AM_CPPFLAGS_%C% = -I$(srcdir)/libc/machine/arm
 
-libc_a_SOURCES += %D%/access.c %D%/aeabi_atexit.c
+libc_a_SOURCES += %D%/access.c %D%/aeabi_atexit.c %D%/sysconf.c
 if MAY_SUPPLY_SYSCALLS
 libc_a_SOURCES += %D%/libcfunc.c %D%/trap.S %D%/syscalls.c
 endif

newlib/libc/sys/arm/sysconf.c

@@ -0,0 +1,34 @@
+/* libc/sys/arm/sysconf.c - The sysconf function */
+
+/* Copyright 2020, STMicroelectronics
+ *
+ * All rights reserved.
+ *
+ * Redistribution, modification, and use in source and binary forms is permitted
+ * provided that the above copyright notice and following paragraph are
+ * duplicated in all such forms.
+ *
+ * This file is distributed WITHOUT ANY WARRANTY; without even the implied
+ * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ */
+
+#include <unistd.h>
+#include <errno.h>
+
+long sysconf(int name)
+{
+  switch (name)
+  {
+  case _SC_PAGESIZE:
+#ifdef SMALL_MEMORY
+    return 128;
+#else
+    return 4096;
+#endif
+
+  default:
+    errno = EINVAL;
+    return -1;
+  }
+  return -1; /* Can't get here */
+}