linux-user: factor out reading of /proc/self/maps

Unfortunately reading /proc/self/maps is still considered the gold
standard for a process finding out about it's own memory layout. As we
will want this data in other contexts soon factor out the code to read
and parse the data. Rather than just blindly copying the existing
sscanf based code we use a more modern glib version of the parsing
code to make a more general purpose map structure.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20200403191150.863-9-alex.bennee@linaro.org>

include/qemu/selfmap.h

@@ -0,0 +1,44 @@
+/*
+ * Utility functions to read our own memory map
+ *
+ * Copyright (c) 2020 Linaro Ltd
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#ifndef _SELFMAP_H_
+#define _SELFMAP_H_
+
+typedef struct {
+    unsigned long start;
+    unsigned long end;
+
+    /* flags */
+    bool is_read;
+    bool is_write;
+    bool is_exec;
+    bool is_priv;
+
+    unsigned long offset;
+    gchar *dev;
+    uint64_t inode;
+    gchar *path;
+} MapInfo;
+
+
+/**
+ * read_self_maps:
+ *
+ * Read /proc/self/maps and return a list of MapInfo structures.
+ */
+GSList *read_self_maps(void);
+
+/**
+ * free_self_maps:
+ * @info: a GSlist
+ *
+ * Free a list of MapInfo structures.
+ */
+void free_self_maps(GSList *info);
+
+#endif /* _SELFMAP_H_ */

linux-user/syscall.c

@@ -117,6 +117,7 @@
 
 #include "qemu.h"
 #include "qemu/guest-random.h"
+#include "qemu/selfmap.h"
 #include "user/syscall-trace.h"
 #include "qapi/error.h"
 #include "fd-trans.h"
@@ -7232,45 +7233,45 @@ static int open_self_maps(void *cpu_env, int fd)
 {
     CPUState *cpu = env_cpu((CPUArchState *)cpu_env);
     TaskState *ts = cpu->opaque;
-    FILE *fp;
-    char *line = NULL;
-    size_t len = 0;
-    ssize_t read;
+    GSList *map_info = read_self_maps();
+    GSList *s;
 
-    fp = fopen("/proc/self/maps", "r");
-    if (fp == NULL) {
-        return -1;
-    }
+    for (s = map_info; s; s = g_slist_next(s)) {
+        MapInfo *e = (MapInfo *) s->data;
 
-    while ((read = getline(&line, &len, fp)) != -1) {
-        int fields, dev_maj, dev_min, inode;
-        uint64_t min, max, offset;
-        char flag_r, flag_w, flag_x, flag_p;
-        char path[512] = "";
-        fields = sscanf(line, "%"PRIx64"-%"PRIx64" %c%c%c%c %"PRIx64" %x:%x %d"
-                        " %512s", &min, &max, &flag_r, &flag_w, &flag_x,
-                        &flag_p, &offset, &dev_maj, &dev_min, &inode, path);
-
-        if ((fields < 10) || (fields > 11)) {
-            continue;
-        }
-        if (h2g_valid(min)) {
+        if (h2g_valid(e->start)) {
+            unsigned long min = e->start;
+            unsigned long max = e->end;
             int flags = page_get_flags(h2g(min));
-            max = h2g_valid(max - 1) ? max : (uintptr_t)g2h(GUEST_ADDR_MAX) + 1;
+            const char *path;
+
+            max = h2g_valid(max - 1) ?
+                max : (uintptr_t) g2h(GUEST_ADDR_MAX) + 1;
+
             if (page_check_range(h2g(min), max - min, flags) == -1) {
                 continue;
             }
+
             if (h2g(min) == ts->info->stack_limit) {
-                pstrcpy(path, sizeof(path), "      [stack]");
+                path = "      [stack]";
+            } else {
+                path = e->path;
             }
+
             dprintf(fd, TARGET_ABI_FMT_ptr "-" TARGET_ABI_FMT_ptr
-                    " %c%c%c%c %08" PRIx64 " %02x:%02x %d %s%s\n",
-                    h2g(min), h2g(max - 1) + 1, flag_r, flag_w,
-                    flag_x, flag_p, offset, dev_maj, dev_min, inode,
-                    path[0] ? "         " : "", path);
+                    " %c%c%c%c %08" PRIx64 " %s %"PRId64" %s%s\n",
+                    h2g(min), h2g(max - 1) + 1,
+                    e->is_read ? 'r' : '-',
+                    e->is_write ? 'w' : '-',
+                    e->is_exec ? 'x' : '-',
+                    e->is_priv ? 'p' : '-',
+                    (uint64_t) e->offset, e->dev, e->inode,
+                    path ? "         " : "", path ? path : "");
         }
     }
 
+    free_self_maps(map_info);
+
 #ifdef TARGET_VSYSCALL_PAGE
     /*
      * We only support execution from the vsyscall page.
@@ -7281,9 +7282,6 @@ static int open_self_maps(void *cpu_env, int fd)
             TARGET_VSYSCALL_PAGE, TARGET_VSYSCALL_PAGE + TARGET_PAGE_SIZE);
 #endif
 
-    free(line);
-    fclose(fp);
-
     return 0;
 }
 

util/Makefile.objs

@@ -63,3 +63,4 @@ util-obj-y += guest-random.o
 util-obj-$(CONFIG_GIO) += dbus.o
 dbus.o-cflags = $(GIO_CFLAGS)
 dbus.o-libs = $(GIO_LIBS)
+util-obj-$(CONFIG_USER_ONLY) += selfmap.o

util/selfmap.c

@@ -0,0 +1,78 @@
+/*
+ * Utility function to get QEMU's own process map
+ *
+ * Copyright (c) 2020 Linaro Ltd
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/cutils.h"
+#include "qemu/selfmap.h"
+
+GSList *read_self_maps(void)
+{
+    gchar *maps;
+    GSList *map_info = NULL;
+
+    if (g_file_get_contents("/proc/self/maps", &maps, NULL, NULL)) {
+        gchar **lines = g_strsplit(maps, "\n", 0);
+        int i, entries = g_strv_length(lines);
+
+        for (i = 0; i < entries; i++) {
+            gchar **fields = g_strsplit(lines[i], " ", 6);
+            if (g_strv_length(fields) > 4) {
+                MapInfo *e = g_new0(MapInfo, 1);
+                int errors;
+                const char *end;
+
+                errors  = qemu_strtoul(fields[0], &end, 16, &e->start);
+                errors += qemu_strtoul(end + 1, NULL, 16, &e->end);
+
+                e->is_read  = fields[1][0] == 'r';
+                e->is_write = fields[1][1] == 'w';
+                e->is_exec  = fields[1][2] == 'x';
+                e->is_priv  = fields[1][3] == 'p';
+
+                errors += qemu_strtoul(fields[2], NULL, 16, &e->offset);
+                e->dev = g_strdup(fields[3]);
+                errors += qemu_strtou64(fields[4], NULL, 10, &e->inode);
+
+                /*
+                 * The last field may have leading spaces which we
+                 * need to strip.
+                 */
+                if (g_strv_length(fields) == 6) {
+                    e->path = g_strdup(g_strchug(fields[5]));
+                }
+                map_info = g_slist_prepend(map_info, e);
+            }
+
+            g_strfreev(fields);
+        }
+        g_strfreev(lines);
+        g_free(maps);
+    }
+
+    /* ensure the map data is in the same order we collected it */
+    return g_slist_reverse(map_info);
+}
+
+/**
+ * free_self_maps:
+ * @info: a GSlist
+ *
+ * Free a list of MapInfo structures.
+ */
+static void free_info(gpointer data)
+{
+    MapInfo *e = (MapInfo *) data;
+    g_free(e->dev);
+    g_free(e->path);
+    g_free(e);
+}
+
+void free_self_maps(GSList *info)
+{
+    g_slist_free_full(info, &free_info);
+}