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>

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',
 ))

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
+}

include/user/mmap-min-addr.h

@@ -0,0 +1,12 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef USER_MMAP_MIN_ADDR_H
+#define USER_MMAP_MIN_ADDR_H
+
+#ifndef CONFIG_USER_ONLY
+#error Cannot include this header from system emulation
+#endif
+
+extern uintptr_t mmap_min_addr;
+
+#endif

linux-user/elfload.c

@@ -14,6 +14,7 @@
 #include "exec/translation-block.h"
 #include "exec/tswap.h"
 #include "user/guest-base.h"
+#include "user/mmap-min-addr.h"
 #include "user-internals.h"
 #include "signal-common.h"
 #include "loader.h"

linux-user/main.c

@@ -39,6 +39,7 @@
 #include "qemu/module.h"
 #include "qemu/plugin.h"
 #include "user/guest-base.h"
+#include "user/mmap-min-addr.h"
 #include "user/page-protection.h"
 #include "exec/gdbstub.h"
 #include "gdbstub/user.h"
@@ -78,7 +79,6 @@ static envlist_t *envlist;
 static const char *cpu_model;
 static const char *cpu_type;
 static const char *seed_optarg;
-unsigned long mmap_min_addr;
 uintptr_t guest_base;
 bool have_guest_base;
 
@@ -914,35 +914,8 @@ int main(int argc, char **argv, char **envp)
     target_environ = envlist_to_environ(envlist, NULL);
     envlist_free(envlist);
 
-    /*
-     * 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;
-
-        if ((fp = fopen("/proc/sys/vm/mmap_min_addr", "r")) != NULL) {
-            unsigned long tmp;
-            if (fscanf(fp, "%lu", &tmp) == 1 && tmp != 0) {
-                mmap_min_addr = MAX(tmp, host_page_size);
-                qemu_log_mask(CPU_LOG_PAGE, "host mmap_min_addr=0x%lx\n",
-                              mmap_min_addr);
-            }
-            fclose(fp);
-        }
-    }
-
-    /*
-     * We prefer to not make NULL pointers accessible to QEMU.
-     * If we're in a chroot with no /proc, fall back to 1 page.
-     */
-    if (mmap_min_addr == 0) {
-        mmap_min_addr = host_page_size;
-        qemu_log_mask(CPU_LOG_PAGE,
-                      "host mmap_min_addr=0x%lx (fallback)\n",
-                      mmap_min_addr);
-    }
+    qemu_log_mask(CPU_LOG_PAGE, "host mmap_min_addr=0x%" PRIxPTR "\n",
+                  mmap_min_addr);
 
     /*
      * Prepare copy of argv vector for target.

linux-user/mmap.c

@@ -24,6 +24,7 @@
 #include "exec/mmap-lock.h"
 #include "qemu.h"
 #include "user/page-protection.h"
+#include "user/mmap-min-addr.h"
 #include "user-internals.h"
 #include "user-mmap.h"
 #include "target_mman.h"

linux-user/user-internals.h

@@ -29,7 +29,6 @@ void init_task_state(TaskState *ts);
 void task_settid(TaskState *);
 void stop_all_tasks(void);
 extern const char *qemu_uname_release;
-extern unsigned long mmap_min_addr;
 
 typedef struct IOCTLEntry IOCTLEntry;