Make config/gen/platform/generic/sysmem.c more generic.

Include the two most likely methods (sysconf and sysctl) in the
generic file, based on various #ifdef probes.  This way, new systems
are more likely to work without first needing their own sysmem.c file.

If neither sysconf() nor sysctl() seems to work, assume a default of
512 MB.  One could certainly argue for putting an error message here
instead.

Signed-off-by: Jonathan "Duke" Leto <jonathan@leto.net>

MANIFEST

@@ -240,7 +240,6 @@ config/gen/platform/cygwin/math.c                           []
 config/gen/platform/darwin/begin.c                          []
 config/gen/platform/darwin/hires_timer.c                    []
 config/gen/platform/darwin/sysmem.c                         []
-config/gen/platform/freebsd/sysmem.c                        []
 config/gen/platform/generic/dl.c                            []
 config/gen/platform/generic/dl.h                            []
 config/gen/platform/generic/env.c                           []
@@ -264,7 +263,6 @@ config/gen/platform/ia64/asm.s                              []
 config/gen/platform/netbsd/math.c                           []
 config/gen/platform/netbsd/misc.c                           []
 config/gen/platform/netbsd/misc.h                           []
-config/gen/platform/netbsd/sysmem.c                         []
 config/gen/platform/openbsd/math.c                          []
 config/gen/platform/openbsd/memexec.c                       []
 config/gen/platform/openbsd/misc.h                          []

config/auto/headers.pm

@@ -97,7 +97,7 @@ sub _list_extra_headers {
     # the header.
     my @extra_headers = qw(malloc.h fcntl.h setjmp.h pthread.h signal.h
         sys/types.h sys/socket.h netinet/in.h arpa/inet.h
-        sys/stat.h sysexit.h limits.h);
+        sys/stat.h sysexit.h limits.h sys/sysctl.h);
 
     # more extra_headers needed on mingw/msys; *BSD fails if they are present
     if ( $conf->data->get('OSNAME_provisional') eq "msys" ) {

config/gen/platform/generic/sysmem.c

@@ -20,11 +20,12 @@ Get system memory information.
 
 */
 
+#include <stdio.h>
 #include <unistd.h>
 #include "parrot/sysmem.h"
 
-#ifdef _SC_PAGESIZE         /* some SVR4 systems omit an underscore */
-#  define  _SC_PAGE_SIZE _SC_PAGESIZE
+#if defined(PARROT_HAS_HEADER_SYSSYSCTL)
+#  include <sys/sysctl.h>
 #endif
 
 /*
@@ -37,10 +38,59 @@ Get information about available physical memory.
 
 */
 
+/*
+ * The POSIX name is _SC_PAGESIZE, but apparently some systems
+ * require _SC_PAGE_SIZE instead.   (Specific citations would
+ * be useful.)
+ */
+#if !defined(_SC_PAGESIZE) && defined(_SC_PAGE_SIZE)
+#  define  _SC_PAGESIZE _SC_PAGE_SIZE
+#endif
+
 size_t
 Parrot_sysmem_amount(PARROT_INTERP)
 {
-    return sysconf(_SC_AVPHYS_PAGES) * sysconf(_SC_PAGE_SIZE);
+    size_t        memsize = 0;
+
+#if defined(_SC_PAGESIZE) && defined(_SC_AVPHYS_PAGES)
+    /* Method 1:  sysconf().
+     * Works on Linux and Solaris, and probably other SVR4-related systems.
+     * This should really check for #ifdef HAS_SYSCONF, but Configure
+     * doesn't probe for that yet.
+     */
+    memsize = sysconf(_SC_AVPHYS_PAGES) * sysconf(_SC_PAGESIZE);
+
+#elif defined(PARROT_HAS_HEADER_SYSSYSCTL) && defined(CTL_HW) && defined(HW_PHYSMEM)
+
+    /* Method 2:  sysctl().  Works on BSD-derived systems.  Darwin is
+     * slightly different, and has its own implementation.
+     * Configure really should test for HAS_SYSCTL, but, for now, test for
+     * the header sys/sysctl.h and the appropriate constants.
+     */
+
+    int           err = 0;
+    char         *err_msg;
+    unsigned long length = sizeof (memsize);
+
+    int selection[2] = { CTL_HW, HW_PHYSMEM };
+
+    err = sysctl(selection, 2, &memsize, &length, NULL, 0);
+
+    if (err) {
+        err_msg = strerror(err);
+        Parrot_ex_throw_from_c_args(interp, NULL, EXCEPTION_EXTERNAL_ERROR,
+                "sysctl failed: %s", err_msg);
+    }
+
+#else
+    /* Method 3:  Random guess.  Simply guess 512 MB.  This way, parrot
+     * will at least build.  Arguably, one could also just put an error
+     * here and instruct the user to fix it manually.
+     */
+    memsize = 512 * 1024 * 1024;
+#endif
+
+    return memsize;
 }
 
 /*