sd-bus: rework ELF error mapping table magic

The ELF magic cannot work for consumers of our shard library, since they
are in a different module. Hence make all the ELF magic private, and
instead introduce a public function to register additional static
mapping table.

3 files changed, 193 insertions, 65 deletions

diff --git a/src/libsystemd/sd-bus/bus-error.c b/src/libsystemd/sd-bus/bus-error.c
index 47f90c26f..157b8d890 100644
--- a/src/libsystemd/sd-bus/bus-error.c
+++ b/src/libsystemd/sd-bus/bus-error.c
@@ -32,61 +32,54 @@
 #include "sd-bus.h"
 #include "bus-error.h"
 
-#define BUS_ERROR_OOM SD_BUS_ERROR_MAKE_CONST(SD_BUS_ERROR_NO_MEMORY, "Out of memory")
-#define BUS_ERROR_FAILED SD_BUS_ERROR_MAKE_CONST(SD_BUS_ERROR_FAILED, "Operation failed")
-
-SD_BUS_ERROR_MAPPING(sd_bus_standard) = {
-        {"org.freedesktop.DBus.Error.Failed",                           EACCES},
-        {"org.freedesktop.DBus.Error.NoMemory",                         ENOMEM},
-        {"org.freedesktop.DBus.Error.ServiceUnknown",                   EHOSTUNREACH},
-        {"org.freedesktop.DBus.Error.NameHasNoOwner",                   ENXIO},
-        {"org.freedesktop.DBus.Error.NoReply",                          ETIMEDOUT},
-        {"org.freedesktop.DBus.Error.IOError",                          EIO},
-        {"org.freedesktop.DBus.Error.BadAddress",                       EADDRNOTAVAIL},
-        {"org.freedesktop.DBus.Error.NotSupported",                     ENOTSUP},
-        {"org.freedesktop.DBus.Error.LimitsExceeded",                   ENOBUFS},
-        {"org.freedesktop.DBus.Error.AccessDenied",                     EACCES},
-        {"org.freedesktop.DBus.Error.AuthFailed",                       EACCES},
-        {"org.freedesktop.DBus.Error.InteractiveAuthorizationRequired", EACCES},
-        {"org.freedesktop.DBus.Error.NoServer",                         EHOSTDOWN},
-        {"org.freedesktop.DBus.Error.Timeout",                          ETIMEDOUT},
-        {"org.freedesktop.DBus.Error.NoNetwork",                        ENONET},
-        {"org.freedesktop.DBus.Error.AddressInUse",                     EADDRINUSE},
-        {"org.freedesktop.DBus.Error.Disconnected",                     ECONNRESET},
-        {"org.freedesktop.DBus.Error.InvalidArgs",                      EINVAL},
-        {"org.freedesktop.DBus.Error.FileNotFound",                     ENOENT},
-        {"org.freedesktop.DBus.Error.FileExists",                       EEXIST},
-        {"org.freedesktop.DBus.Error.UnknownMethod",                    EBADR},
-        {"org.freedesktop.DBus.Error.UnknownObject",                    EBADR},
-        {"org.freedesktop.DBus.Error.UnknownInterface",                 EBADR},
-        {"org.freedesktop.DBus.Error.UnknownProperty",                  EBADR},
-        {"org.freedesktop.DBus.Error.PropertyReadOnly",                 EROFS},
-        {"org.freedesktop.DBus.Error.UnixProcessIdUnknown",             ESRCH},
-        {"org.freedesktop.DBus.Error.InvalidSignature",                 EINVAL},
-        {"org.freedesktop.DBus.Error.InconsistentMessage",              EBADMSG},
-
-        {"org.freedesktop.DBus.Error.TimedOut",                         ETIMEDOUT},
-        {"org.freedesktop.DBus.Error.MatchRuleInvalid",                 EINVAL},
-        {"org.freedesktop.DBus.Error.InvalidFileContent",               EINVAL},
-        {"org.freedesktop.DBus.Error.MatchRuleNotFound",                ENOENT},
-        {"org.freedesktop.DBus.Error.SELinuxSecurityContextUnknown",    ESRCH},
-        {"org.freedesktop.DBus.Error.ObjectPathInUse",                  EBUSY},
+BUS_ERROR_MAP_ELF_REGISTER const sd_bus_error_map standard_errors[] = {
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.Failed",                           EACCES),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.NoMemory",                         ENOMEM),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.ServiceUnknown",                   EHOSTUNREACH),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.NameHasNoOwner",                   ENXIO),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.NoReply",                          ETIMEDOUT),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.IOError",                          EIO),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.BadAddress",                       EADDRNOTAVAIL),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.NotSupported",                     ENOTSUP),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.LimitsExceeded",                   ENOBUFS),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.AccessDenied",                     EACCES),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.AuthFailed",                       EACCES),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.InteractiveAuthorizationRequired", EACCES),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.NoServer",                         EHOSTDOWN),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.Timeout",                          ETIMEDOUT),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.NoNetwork",                        ENONET),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.AddressInUse",                     EADDRINUSE),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.Disconnected",                     ECONNRESET),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.InvalidArgs",                      EINVAL),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.FileNotFound",                     ENOENT),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.FileExists",                       EEXIST),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.UnknownMethod",                    EBADR),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.UnknownObject",                    EBADR),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.UnknownInterface",                 EBADR),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.UnknownProperty",                  EBADR),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.PropertyReadOnly",                 EROFS),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.UnixProcessIdUnknown",             ESRCH),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.InvalidSignature",                 EINVAL),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.InconsistentMessage",              EBADMSG),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.TimedOut",                         ETIMEDOUT),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.MatchRuleInvalid",                 EINVAL),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.InvalidFileContent",               EINVAL),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.MatchRuleNotFound",                ENOENT),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.SELinuxSecurityContextUnknown",    ESRCH),
+        SD_BUS_ERROR_MAP("org.freedesktop.DBus.Error.ObjectPathInUse",                  EBUSY),
+        SD_BUS_ERROR_MAP_END
 };
 
-extern const sd_bus_name_error_mapping __start_sd_bus_errnomap[];
-extern const sd_bus_name_error_mapping __stop_sd_bus_errnomap[];
+/* GCC maps this magically to the beginning and end of the BUS_ERROR_MAP section */
+extern const sd_bus_error_map __start_BUS_ERROR_MAP[];
+extern const sd_bus_error_map __stop_BUS_ERROR_MAP[];
 
-static int bus_error_mapping_lookup(const char *name, size_t len) {
-        const sd_bus_name_error_mapping *m;
-
-        for (m = __start_sd_bus_errnomap; m < __stop_sd_bus_errnomap; m++)
-                if (m->name && strneq(m->name, name, len))
-                        return m->code;
-
-        return EIO;
-}
+/* Additional maps registered with sd_bus_error_add_map() are in this
+ * NULL terminated array */
+static const sd_bus_error_map **additional_error_maps = NULL;
 
 static int bus_error_name_to_errno(const char *name) {
+        const sd_bus_error_map **map, *m;
         const char *p;
         int r;
 
@@ -102,7 +95,39 @@ static int bus_error_name_to_errno(const char *name) {
                 return r;
         }
 
-        return bus_error_mapping_lookup(name, strlen(name));
+        if (additional_error_maps) {
+                for (map = additional_error_maps; *map; map++) {
+                        for (m = *map;; m++) {
+                                /* For additional error maps the end marker is actually the end marker */
+                                if (m->code == BUS_ERROR_MAP_END_MARKER)
+                                        break;
+
+                                if (streq(m->name, name))
+                                        return m->code;
+                        }
+                }
+        }
+
+        m = __start_BUS_ERROR_MAP;
+        while (m < __stop_BUS_ERROR_MAP) {
+                /* For magic ELF error maps, the end marker might
+                 * appear in the middle of things, since multiple maps
+                 * might appear in the same section. Hence, let's skip
+                 * over it, but realign the pointer to the netx 8byte
+                 * boundary, which is the selected alignment for the
+                 * arrays. */
+                if (m->code == BUS_ERROR_MAP_END_MARKER) {
+                        m = ALIGN8_PTR(m+1);
+                        continue;
+                }
+
+                if (streq(m->name, name))
+                        return m->code;
+
+                m++;
+        }
+
+        return EIO;
 }
 
 static sd_bus_error errno_to_bus_error_const(int error) {
@@ -552,3 +577,31 @@ const char *bus_error_message(const sd_bus_error *e, int error) {
 
         return strerror(error);
 }
+
+_public_ int sd_bus_error_add_map(const sd_bus_error_map *map) {
+        const sd_bus_error_map **maps = NULL;
+        unsigned n = 0;
+
+        assert_return(map, -EINVAL);
+
+        if (additional_error_maps) {
+                for (;; n++) {
+                        if (additional_error_maps[n] == NULL)
+                                break;
+
+                        if (additional_error_maps[n] == map)
+                                return 0;
+                }
+        }
+
+        maps = realloc_multiply(additional_error_maps, sizeof(struct sd_bus_error_map*), n + 2);
+        if (!maps)
+                return -ENOMEM;
+
+
+        maps[n] = map;
+        maps[n+1] = NULL;
+
+        additional_error_maps = maps;
+        return 1;
+}
diff --git a/src/libsystemd/sd-bus/bus-error.h b/src/libsystemd/sd-bus/bus-error.h
index 146948618..56297156a 100644
--- a/src/libsystemd/sd-bus/bus-error.h
+++ b/src/libsystemd/sd-bus/bus-error.h
@@ -26,15 +26,40 @@
 #include "sd-bus.h"
 #include "macro.h"
 
-struct name_error_mapping {
-        const char* name;
-        int code;
-};
-typedef struct name_error_mapping name_error_mapping;
-
 bool bus_error_is_dirty(sd_bus_error *e);
 
 const char *bus_error_message(const sd_bus_error *e, int error);
 
 int bus_error_setfv(sd_bus_error *e, const char *name, const char *format, va_list ap) _printf_(3,0);
 int bus_error_set_errnofv(sd_bus_error *e, int error, const char *format, va_list ap) _printf_(3,0);
+
+#define BUS_ERROR_OOM SD_BUS_ERROR_MAKE_CONST(SD_BUS_ERROR_NO_MEMORY, "Out of memory")
+#define BUS_ERROR_FAILED SD_BUS_ERROR_MAKE_CONST(SD_BUS_ERROR_FAILED, "Operation failed")
+
+/*
+ * There are two ways to register error maps with the error translation
+ * logic: by using BUS_ERROR_MAP_ELF_REGISTER, which however only
+ * works when linked into the same ELF module, or via
+ * sd_bus_error_add_map() which is the official, external API, that
+ * works from any module.
+ *
+ * Note that BUS_ERROR_MAP_ELF_REGISTER has to be used as decorator in
+ * the bus error table, and BUS_ERROR_MAP_ELF_USE has to be used at
+ * least once per compilation unit (i.e. per library), to ensure that
+ * the error map is really added to the final binary.
+ */
+
+#define BUS_ERROR_MAP_ELF_REGISTER                                      \
+        __attribute__ ((__section__("BUS_ERROR_MAP")))                  \
+        __attribute__ ((__used__))                                      \
+        __attribute__ ((aligned(8)))
+
+#define BUS_ERROR_MAP_ELF_USE(errors)                                   \
+        extern const sd_bus_error_map errors[];                         \
+        __attribute__ ((used)) static const sd_bus_error_map * CONCATENATE(errors ## _copy_, __COUNTER__) = errors;
+
+/* We use something exotic as end marker, to ensure people build the
+ * maps using the macsd-ros. */
+#define BUS_ERROR_MAP_END_MARKER -'x'
+
+BUS_ERROR_MAP_ELF_USE(standard_errors);
diff --git a/src/libsystemd/sd-bus/test-bus-error.c b/src/libsystemd/sd-bus/test-bus-error.c
index ae894e39f..f72bcdb6b 100644
--- a/src/libsystemd/sd-bus/test-bus-error.c
+++ b/src/libsystemd/sd-bus/test-bus-error.c
@@ -22,6 +22,8 @@
 #include "sd-bus.h"
 #include "bus-error.h"
 #include "bus-util.h"
+#include "errno-list.h"
+#include "bus-errors.h"
 
 static void test_error(void) {
         _cleanup_bus_error_free_ sd_bus_error error = SD_BUS_ERROR_NULL, second = SD_BUS_ERROR_NULL;
@@ -111,15 +113,24 @@ static void test_error(void) {
         assert_se(sd_bus_error_is_set(&error));
 }
 
-extern const sd_bus_name_error_mapping __start_sd_bus_errnomap[];
-extern const sd_bus_name_error_mapping __stop_sd_bus_errnomap[];
+extern const sd_bus_error_map __start_BUS_ERROR_MAP[];
+extern const sd_bus_error_map __stop_BUS_ERROR_MAP[];
 
 static void dump_mapping_table(void) {
-        const sd_bus_name_error_mapping *m;
+        const sd_bus_error_map *m;
 
         printf("----- errno mappings ------\n");
-        for (m = __start_sd_bus_errnomap; m < __stop_sd_bus_errnomap; m++)
-                printf("%s -> %d\n", m->name, m->code);
+        m = __start_BUS_ERROR_MAP;
+        while (m < __stop_BUS_ERROR_MAP) {
+
+                if (m->code == BUS_ERROR_MAP_END_MARKER) {
+                        m = ALIGN8_PTR(m+1);
+                        continue;
+                }
+
+                printf("%s -> %i/%s\n", strna(m->name), m->code, strna(errno_to_name(m->code)));
+                m ++;
+        }
         printf("---------------------------\n");
 }
 
@@ -130,15 +141,54 @@ static void test_errno_mapping_standard(void) {
         assert_se(sd_bus_error_set(NULL, "System.Error.WHATSIT", NULL) == -EIO);
 }
 
-SD_BUS_ERROR_MAPPING(test) = {
-        {"org.freedesktop.custom-dbus-error", 5},
-        {"org.freedesktop.custom-dbus-error-2", 52},
+BUS_ERROR_MAP_ELF_REGISTER const sd_bus_error_map test_errors[] = {
+        SD_BUS_ERROR_MAP("org.freedesktop.custom-dbus-error", 5),
+        SD_BUS_ERROR_MAP("org.freedesktop.custom-dbus-error-2", 52),
+        SD_BUS_ERROR_MAP_END
+};
+
+BUS_ERROR_MAP_ELF_REGISTER const sd_bus_error_map test_errors2[] = {
+        SD_BUS_ERROR_MAP("org.freedesktop.custom-dbus-error-3", 33),
+        SD_BUS_ERROR_MAP("org.freedesktop.custom-dbus-error-4", 44),
+        SD_BUS_ERROR_MAP("org.freedesktop.custom-dbus-error-33", 333),
+        SD_BUS_ERROR_MAP_END
+};
+
+static const sd_bus_error_map test_errors3[] = {
+        SD_BUS_ERROR_MAP("org.freedesktop.custom-dbus-error-88", 888),
+        SD_BUS_ERROR_MAP("org.freedesktop.custom-dbus-error-99", 999),
+        SD_BUS_ERROR_MAP_END
+};
+
+static const sd_bus_error_map test_errors4[] = {
+        SD_BUS_ERROR_MAP("org.freedesktop.custom-dbus-error-77", 777),
+        SD_BUS_ERROR_MAP("org.freedesktop.custom-dbus-error-78", 778),
+        SD_BUS_ERROR_MAP_END
 };
 
 static void test_errno_mapping_custom(void) {
         assert_se(sd_bus_error_set(NULL, "org.freedesktop.custom-dbus-error", NULL) == -5);
         assert_se(sd_bus_error_set(NULL, "org.freedesktop.custom-dbus-error-2", NULL) == -52);
         assert_se(sd_bus_error_set(NULL, "org.freedesktop.custom-dbus-error-x", NULL) == -EIO);
+        assert_se(sd_bus_error_set(NULL, "org.freedesktop.custom-dbus-error-33", NULL) == -333);
+
+        assert_se(sd_bus_error_set(NULL, "org.freedesktop.custom-dbus-error-88", NULL) == -EIO);
+        assert_se(sd_bus_error_set(NULL, "org.freedesktop.custom-dbus-error-99", NULL) == -EIO);
+        assert_se(sd_bus_error_set(NULL, "org.freedesktop.custom-dbus-error-77", NULL) == -EIO);
+
+        assert_se(sd_bus_error_add_map(test_errors3) > 0);
+        assert_se(sd_bus_error_set(NULL, "org.freedesktop.custom-dbus-error-88", NULL) == -888);
+        assert_se(sd_bus_error_add_map(test_errors4) > 0);
+        assert_se(sd_bus_error_add_map(test_errors4) == 0);
+        assert_se(sd_bus_error_add_map(test_errors3) == 0);
+
+        assert_se(sd_bus_error_set(NULL, "org.freedesktop.custom-dbus-error-99", NULL) == -999);
+        assert_se(sd_bus_error_set(NULL, "org.freedesktop.custom-dbus-error-77", NULL) == -777);
+        assert_se(sd_bus_error_set(NULL, "org.freedesktop.custom-dbus-error-78", NULL) == -778);
+        assert_se(sd_bus_error_set(NULL, "org.freedesktop.custom-dbus-error-2", NULL) == -52);
+        assert_se(sd_bus_error_set(NULL, "org.freedesktop.custom-dbus-error-y", NULL) == -EIO);
+
+        assert_se(sd_bus_error_set(NULL, BUS_ERROR_NO_SUCH_UNIT, NULL) == -ENOENT);
 }
 
 int main(int argc, char *argv[]) {