Userspace guest address offsetting

Re-implement GUEST_BASE support.
Offset guest ddress space by default if the guest binary contains
regions below the host mmap_min_addr.
Implement support for i386, x86-64 and arm hosts.

Signed-off-by: Riku Voipio <riku.voipio@iki.fi>
Signed-off-by: Paul Brook <paul@codesourcery.com>

linux-user/elfload.c

@@ -1545,6 +1545,29 @@ int load_elf_binary(struct linux_binprm * bprm, struct target_pt_regs * regs,
     info->mmap = 0;
     elf_entry = (abi_ulong) elf_ex.e_entry;
 
+#if defined(CONFIG_USE_GUEST_BASE)
+    /*
+     * In case where user has not explicitly set the guest_base, we
+     * probe here that should we set it automatically.
+     */
+    if (!have_guest_base) {
+        /*
+         * Go through ELF program header table and find out whether
+	 * any of the segments drop below our current mmap_min_addr and
+         * in that case set guest_base to corresponding address.
+         */
+        for (i = 0, elf_ppnt = elf_phdata; i < elf_ex.e_phnum;
+            i++, elf_ppnt++) {
+            if (elf_ppnt->p_type != PT_LOAD)
+                continue;
+            if (HOST_PAGE_ALIGN(elf_ppnt->p_vaddr) < mmap_min_addr) {
+                guest_base = HOST_PAGE_ALIGN(mmap_min_addr);
+                break;
+            }
+        }
+    }
+#endif /* CONFIG_USE_GUEST_BASE */
+
     /* Do this so that we can load the interpreter, if need be.  We will
        change some of these later */
     info->rss = 0;

linux-user/main.c

@@ -39,6 +39,11 @@
 char *exec_path;
 
 int singlestep;
+#if defined(CONFIG_USE_GUEST_BASE)
+unsigned long mmap_min_addr;
+unsigned long guest_base;
+int have_guest_base;
+#endif
 
 static const char *interp_prefix = CONFIG_QEMU_PREFIX;
 const char *qemu_uname_release = CONFIG_UNAME_RELEASE;
@@ -2320,6 +2325,9 @@ static void usage(void)
            "-E var=value      sets/modifies targets environment variable(s)\n"
            "-U var            unsets targets environment variable(s)\n"
            "-0 argv0          forces target process argv[0] to be argv0\n"
+#if defined(CONFIG_USE_GUEST_BASE)
+           "-B address        set guest_base address to address\n"
+#endif
            "\n"
            "Debug options:\n"
            "-d options   activate log (logfile=%s)\n"
@@ -2495,6 +2503,11 @@ int main(int argc, char **argv, char **envp)
 #endif
                 exit(1);
             }
+#if defined(CONFIG_USE_GUEST_BASE)
+        } else if (!strcmp(r, "B")) {
+           guest_base = strtol(argv[optind++], NULL, 0);
+           have_guest_base = 1;
+#endif
         } else if (!strcmp(r, "drop-ld-preload")) {
             (void) envlist_unsetenv(envlist, "LD_PRELOAD");
         } else if (!strcmp(r, "singlestep")) {
@@ -2572,6 +2585,35 @@ int main(int argc, char **argv, char **envp)
     target_environ = envlist_to_environ(envlist, NULL);
     envlist_free(envlist);
 
+#if defined(CONFIG_USE_GUEST_BASE)
+    /*
+     * Now that page sizes are configured in cpu_init() we can do
+     * proper page alignment for guest_base.
+     */
+    guest_base = HOST_PAGE_ALIGN(guest_base);
+
+    /*
+     * Read in mmap_min_addr kernel parameter.  This value is used
+     * When loading the ELF image to determine whether guest_base
+     * is needed.
+     *
+     * When user has explicitly set the quest base, we skip this
+     * test.
+     */
+    if (!have_guest_base) {
+        FILE *fp;
+
+        if ((fp = fopen("/proc/sys/vm/mmap_min_addr", "r")) != NULL) {
+            unsigned long tmp;
+            if (fscanf(fp, "%lu", &tmp) == 1) {
+                mmap_min_addr = tmp;
+                qemu_log("host mmap_min_addr=0x%lx\n", mmap_min_addr);
+            }
+            fclose(fp);
+        }
+    }
+#endif /* CONFIG_USE_GUEST_BASE */
+
     /*
      * Prepare copy of argv vector for target.
      */
@@ -2622,6 +2664,9 @@ int main(int argc, char **argv, char **envp)
     free(target_environ);
 
     if (qemu_log_enabled()) {
+#if defined(CONFIG_USE_GUEST_BASE)
+        qemu_log("guest_base  0x%lx\n", guest_base);
+#endif
         log_page_dump();
 
         qemu_log("start_brk   0x" TARGET_ABI_FMT_lx "\n", info->start_brk);

linux-user/qemu.h

@@ -133,6 +133,9 @@ void init_task_state(TaskState *ts);
 void task_settid(TaskState *);
 void stop_all_tasks(void);
 extern const char *qemu_uname_release;
+#if defined(CONFIG_USE_GUEST_BASE)
+extern unsigned long mmap_min_addr;
+#endif
 
 /* ??? See if we can avoid exposing so much of the loader internals.  */
 /*