common-user: Move mmap_min_addr from linux-user

Introduce user/mmap-min-addr.h.  Initialize the variable
from a constructor instead of main.

Reviewed-by: Helge Deller <deller@gmx.de>
Reviewed-by: Warner Losh <imp@bsdimp.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

2 files changed, 38 insertions, 0 deletions

diff --git a/common-user/meson.build b/common-user/meson.build
index ac9de5b9e3..f9e2e83f9a 100644
--- a/common-user/meson.build
+++ b/common-user/meson.build
@@ -5,6 +5,7 @@ endif
 common_user_inc += include_directories('host/' / host_arch)
 
 user_ss.add(files(
+  'mmap-min-addr.c',
   'safe-syscall.S',
   'safe-syscall-error.c',
 ))
diff --git a/common-user/mmap-min-addr.c b/common-user/mmap-min-addr.c
new file mode 100644
index 0000000000..b2b3762386
--- /dev/null
+++ b/common-user/mmap-min-addr.c
@@ -0,0 +1,37 @@
+/*
+ * Utility function to get the minimum mmap address.
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "user/mmap-min-addr.h"
+
+uintptr_t mmap_min_addr;
+
+static void __attribute__((constructor)) init(void)
+{
+#ifdef __linux__
+    /*
+     * We prefer to not make NULL pointers accessible to QEMU.
+     * If something goes wrong below, fall back to 1 page.
+     */
+    size_t min_addr = qemu_real_host_page_size();
+    /*
+     * Read in mmap_min_addr kernel parameter.  This value is used
+     * When loading the ELF image to determine whether guest_base
+     * is needed.  It is also used in mmap_find_vma.
+     */
+    FILE *fp = fopen("/proc/sys/vm/mmap_min_addr", "r");
+
+    if (fp) {
+        unsigned long tmp;
+        if (fscanf(fp, "%lu", &tmp) == 1 && tmp != 0) {
+            min_addr = MAX(min_addr, tmp);
+        }
+        fclose(fp);
+    }
+    mmap_min_addr = min_addr;
+#else
+# error
+#endif
+}