Add --disable-syscall.

This resolves #517.

INSTALL

@@ -203,6 +203,11 @@ any of the following arguments (not a definitive list) to 'configure':
     most extreme case increases physical memory usage for the 16 KiB size class
     to 20 KiB.
 
+--disable-syscall
+    Disable use of syscall(2) rather than {open,read,write,close}(2).  This is
+    intended as a workaround for systems that place security limitations on
+    syscall(2).
+
 --with-xslroot=<path>
     Specify where to find DocBook XSL stylesheets when building the
     documentation.

configure.ac

@@ -1366,20 +1366,33 @@ if test "x${je_cv_mach_absolute_time}" = "xyes" ; then
   AC_DEFINE([JEMALLOC_HAVE_MACH_ABSOLUTE_TIME])
 fi
 
-dnl Check if syscall(2) is usable.  Treat warnings as errors, so that e.g. OS X
-dnl 10.12's deprecation warning prevents use.
-SAVED_CFLAGS="${CFLAGS}"
-JE_CFLAGS_APPEND([-Werror])
-JE_COMPILABLE([syscall(2)], [
+dnl Use syscall(2) (if available) by default.
+AC_ARG_ENABLE([syscall],
+  [AS_HELP_STRING([--disable-syscall], [Disable use of syscall(2)])],
+[if test "x$enable_syscall" = "xno" ; then
+  enable_syscall="0"
+else
+  enable_syscall="1"
+fi
+],
+[enable_syscall="1"]
+)
+if test "x$enable_syscall" = "x1" ; then
+  dnl Check if syscall(2) is usable.  Treat warnings as errors, so that e.g. OS
+  dnl X 10.12's deprecation warning prevents use.
+  SAVED_CFLAGS="${CFLAGS}"
+  JE_CFLAGS_APPEND([-Werror])
+  JE_COMPILABLE([syscall(2)], [
 #include <sys/syscall.h>
 #include <unistd.h>
 ], [
 	syscall(SYS_write, 2, "hello", 5);
 ],
-              [je_cv_syscall])
-CFLAGS="${SAVED_CFLAGS}"
-if test "x$je_cv_syscall" = "xyes" ; then
-  AC_DEFINE([JEMALLOC_HAVE_SYSCALL], [ ])
+                [je_cv_syscall])
+  CFLAGS="${SAVED_CFLAGS}"
+  if test "x$je_cv_syscall" = "xyes" ; then
+    AC_DEFINE([JEMALLOC_USE_SYSCALL], [ ])
+  fi
 fi
 
 dnl Check if the GNU-specific secure_getenv function exists.

include/jemalloc/internal/jemalloc_internal_defs.h.in

@@ -66,8 +66,8 @@
  */
 #undef JEMALLOC_OSSPIN
 
-/* Defined if syscall(2) is available. */
-#undef JEMALLOC_HAVE_SYSCALL
+/* Defined if syscall(2) is usable. */
+#undef JEMALLOC_USE_SYSCALL
 
 /*
  * Defined if secure_getenv(3) is available.

src/pages.c

@@ -219,7 +219,7 @@ os_overcommits_proc(void)
 	char buf[1];
 	ssize_t nread;
 
-#if defined(JEMALLOC_HAVE_SYSCALL) && defined(SYS_open)
+#if defined(JEMALLOC_USE_SYSCALL) && defined(SYS_open)
 	fd = (int)syscall(SYS_open, "/proc/sys/vm/overcommit_memory", O_RDONLY);
 #else
 	fd = open("/proc/sys/vm/overcommit_memory", O_RDONLY);
@@ -227,13 +227,13 @@ os_overcommits_proc(void)
 	if (fd == -1)
 		return (false); /* Error. */
 
-#if defined(JEMALLOC_HAVE_SYSCALL) && defined(SYS_read)
+#if defined(JEMALLOC_USE_SYSCALL) && defined(SYS_read)
 	nread = (ssize_t)syscall(SYS_read, fd, &buf, sizeof(buf));
 #else
 	nread = read(fd, &buf, sizeof(buf));
 #endif
 
-#if defined(JEMALLOC_HAVE_SYSCALL) && defined(SYS_close)
+#if defined(JEMALLOC_USE_SYSCALL) && defined(SYS_close)
 	syscall(SYS_close, fd);
 #else
 	close(fd);

src/util.c

@@ -49,7 +49,7 @@ static void
 wrtmessage(void *cbopaque, const char *s)
 {
 
-#if defined(JEMALLOC_HAVE_SYSCALL) && defined(SYS_write)
+#if defined(JEMALLOC_USE_SYSCALL) && defined(SYS_write)
 	/*
 	 * Use syscall(2) rather than write(2) when possible in order to avoid
 	 * the possibility of memory allocation within libc.  This is necessary