ABI change in libfm.so.4 in recent commit

[mtasaka]

Looks like due to
b0545e0
2854a4c

the size of struct _FmConfig got changed and this resulted in ABI change in libfm.so.4.

Downside bug report
https://bugzilla.redhat.com/show_bug.cgi?id=2333955

is perhaps due to the following condition

• pcmanfm is using lxde/pcmanfm@836c77c
  • the above pcmanfm is compiled with libfm d9935ec
• Then system libfm is upgraded to cea6607

libfm between these commits includes 2854a4c

Then pcmanfm causes segfault.
The downside bug's backtrace seems to be sugesting that _cfg_mon in _FmConfig is not initialized to 0 despite that g_object_new is called.

[mtasaka]

Actually _cfg_mon seems to be 0-initialized, however gdb shows that later cfg->_cfg_mon gets modified at the wrong place:

tasaka1@localhost ~]$ gdb --args pcmanfm
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Reading symbols from pcmanfm...
Reading symbols from /usr/lib/debug/usr/bin/pcmanfm-1.3.2^20241203git836c77c8-1.fc41.x86_64.debug...
(gdb) set style enabled off
(gdb) break fm_config_init
Function "fm_config_init" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (fm_config_init) pending.
(gdb) r
Starting program: /usr/bin/pcmanfm 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

(pcmanfm:719630): dbind-WARNING **: 16:26:10.627: Couldn't connect to accessibility bus: Failed to connect to socket /root/.cache/at-spi/bus_0: 許可がありません
Breakpoint 1, fm_config_init (self=0x4bc930 [FmConfig])
    at /usr/src/debug/libfm-1.3.2^20241216gitfb651b87-1.fc41.x86_64/libfm/_BUILDDIR_gtk3/../src/base/fm-config.c:137
137     {
(gdb) bt

#0  fm_config_init (self=0x4bc930 [FmConfig])
    at /usr/src/debug/libfm-1.3.2^20241216gitfb651b87-1.fc41.x86_64/libfm/_BUILDDIR_gtk3/../src/base/fm-config.c:137
#1  0x00007ffff6e9af27 in g_type_create_instance (type=0x4c00f0 [FmAppConfig/FmConfig]) at ../gobject/gtype.c:1945
#2  0x00007ffff6e801c4 in g_object_new_internal (class=0x4c0360, params=0x0, n_params=0) at ../gobject/gobject.c:2606
#3  0x00007ffff6e817de in g_object_new_internal (class=<optimized out>, params=<optimized out>, n_params=<optimized out>)
    at ../gobject/gobject.c:2603
#4  g_object_new_with_properties (object_type=<optimized out>, n_properties=<optimized out>, names=names@entry=0x0, values=values@entry=0x0)
    at ../gobject/gobject.c:2769
#5  0x00007ffff6e82801 in g_object_new (object_type=<optimized out>, first_property_name=first_property_name@entry=0x0)
    at ../gobject/gobject.c:2415
#6  0x0000000000407704 in fm_app_config_new () at /usr/src/debug/pcmanfm-1.3.2^20241203git836c77c8-1.fc41.x86_64/pcmanfm/src/app-config.c:543
#7  main (argc=<optimized out>, argv=<optimized out>) at /usr/src/debug/pcmanfm-1.3.2^20241203git836c77c8-1.fc41.x86_64/pcmanfm/src/pcmanfm.c:253
(gdb) p *self

$1 = {parent = {g_type_instance = {g_class = 0x4bff00 [g_type: FmConfig]}, ref_count = 1, qdata = 0x0}, _cfg_name = 0x0, terminal = 0x0, 
  archiver = 0x0, big_icon_size = 0, small_icon_size = 0, pane_icon_size = 0, thumbnail_size = 0, thumbnail_max = 0, auto_selection_delay = 0, 
  drop_default_action = 0, single_click = 0, middle_click = 0, use_trash = 0, confirm_del = 0, confirm_trash = 0, show_thumbnail = 0, 
  thumbnail_local = 0, show_internal_volumes = 0, si_unit = 0, advanced_mode = 0, force_startup_notify = 0, date_iso_8601 = 0, 
  backup_as_hidden = 0, no_usb_trash = 0, no_child_non_expandable = 0, show_full_names = 0, shadow_hidden = 0, places_home = 0, 
  places_desktop = 0, places_applications = 0, places_trash = 0, places_root = 0, places_computer = 0, places_network = 0, places_unmounted = 0, 
  only_user_templates = 0, template_run_app = 0, template_type_once = 0, defer_content_test = 0, quick_exec = 0, modules_blacklist = 0x0, 
  modules_whitelist = 0x0, system_modules_blacklist = 0x0, list_view_size_units = 0x0, format_cmd = 0x0, smart_desktop_autodrop = 0, 
  saved_search = 0x0, _reserved1 = 0x0, _reserved2 = 0x0, _reserved3 = 0x0, _reserved4 = 0x0, _reserved5 = 0x0, _reserved6 = 0x0, 
  _reserved7 = 0x0, _cfg_mon = 0x0}
(gdb) p &(self->_cfg_mon)

$2 = (GFileMonitor **) 0x4bca68
(gdb) watch *((long *)0x4b0x4bca68

Hardware watchpoint 2: *((long *)0x4bca68)
(gdb) c

Continuing.
[New Thread 0x7fffe7c006c0 (LWP 719694)]
[New Thread 0x7fffe72006c0 (LWP 719695)]
[New Thread 0x7fffe68006c0 (LWP 719696)]

Thread 1 "pcmanfm" hit Hardware watchpoint 2: *((long *)0x4bca68)

Old value = 0
New value = 5124544
_cfg_monitor_add (cfg=0x4bc930, path=0x4bde30 "/home/tasaka1/.config/libfm/libfm.conf")
    at /usr/src/debug/libfm-1.3.2^20241216gitfb651b87-1.fc41.x86_64/libfm/_BUILDDIR_gtk3/../src/base/fm-config.c:107
107         g_object_unref(gf);
Missing debuginfo, try: dnf debuginfo-install gvfs-client-1.56.1-1.fc41.x86_64

(gdb) c

Continuing.

Thread 1 "pcmanfm" hit Hardware watchpoint 2: *((long *)0x4bca68)

Old value = 5124544
New value = 4294967296
fm_app_config_init (cfg=0x4bc930) at /usr/src/debug/pcmanfm-1.3.2^20241203git836c77c8-1.fc41.x86_64/pcmanfm/src/app-config.c:495
fm_app_config_init (cfg=0x4bc930) at /usr/src/debug/pcmanfm-1.3.2^20241203git836c77c8-1.fc41.x86_64/pcmanfm/src/app-config.c:495
495         cfg->max_tab_chars = 32;

(gdb) li

490     
491         cfg->desktop_section.desktop_fg.red = cfg->desktop_section.desktop_fg.green = cfg->desktop_section.desktop_fg.blue = 65535;
492         cfg->win_width = 640;
493         cfg->win_height = 480;
494         cfg->splitter_pos = 150;
495         cfg->max_tab_chars = 32;
496         cfg->media_in_new_tab = FALSE;
497         cfg->desktop_folder_new_win = FALSE;
498     
499         cfg->side_pane_mode = FM_SP_PLACES;
(gdb) c

Continuing.
[New Thread 0x7fffe5e006c0 (LWP 719757)]
[New Thread 0x7fffe54006c0 (LWP 719758)]

Thread 1 "pcmanfm" hit Hardware watchpoint 2: *((long *)0x4bca68)

Old value = 4294967296
New value = 4294967297
fm_key_file_get_int (kf=kf@entry=0x5725c0, grp=grp@entry=0x43536c "config", key=key@entry=0x43535d "bm_open_method", val=val@entry=0x4bca68)
    at /usr/src/debug/libfm-1.3.2^20241216gitfb651b87-1.fc41.x86_64/libfm/_BUILDDIR_gtk3/../src/base/fm-utils.c:217
217             g_free(str);

(gdb) bt

#0  fm_key_file_get_int (kf=kf@entry=0x5725c0, grp=grp@entry=0x43536c "config", key=key@entry=0x43535d "bm_open_method", val=val@entry=0x4bca68)
    at /usr/src/debug/libfm-1.3.2^20241216gitfb651b87-1.fc41.x86_64/libfm/_BUILDDIR_gtk3/../src/base/fm-utils.c:217
#1  0x0000000000412437 in fm_app_config_load_from_key_file (cfg=cfg@entry=0x4bc930, kf=kf@entry=0x5725c0)
    at /usr/src/debug/pcmanfm-1.3.2^20241203git836c77c8-1.fc41.x86_64/pcmanfm/src/app-config.c:662
#2  0x0000000000407a7c in fm_app_config_load_from_profile (cfg=0x4bc930, name=0x436908 "default")
    at /usr/src/debug/pcmanfm-1.3.2^20241203git836c77c8-1.fc41.x86_64/pcmanfm/src/app-config.c:846
#3  main (argc=<optimized out>, argv=<optimized out>) at /usr/src/debug/pcmanfm-1.3.2^20241203git836c77c8-1.fc41.x86_64/pcmanfm/src/pcmanfm.c:273
(gdb) li

212     {
213         char* str = g_key_file_get_value(kf, grp, key, NULL);
214         if(G_LIKELY(str))
215         {
216             *val = atoi(str);
217             g_free(str);
218         }
219         return str != NULL;
220     }
221     
(gdb) c

Continuing.
[Thread 0x7fffe54006c0 (LWP 719758) exited]
[New Thread 0x7fffe54006c0 (LWP 719818)]
[New Thread 0x7fffe4a006c0 (LWP 719819)]
[New Thread 0x7fffdde006c0 (LWP 719820)]
[New Thread 0x7fffdd4006c0 (LWP 719822)]

(
Thread 1 "pcmanfm" received signal SIGSEGV, Segmentation fault.
g_type_check_instance (type_instance=0x100000001) at ../gobject/gtype.c:4257
4257          if (type_instance->g_class)
Missing debuginfo, try: dnf debuginfo-install ibus-gtk3-1.5.31-1.fc41.x86_64
Missing debuginfo, try: dnf debuginfo-install ibus-libs-1.5.31-1.fc41.x86_64
Missing debuginfo, try: dnf debuginfo-install rsvg-pixbuf-loader-2.59.2-1.fc41.x86_64
Missing debuginfo, try: dnf debuginfo-install librsvg2-2.59.2-1.fc41.x86_64

(gdb) bt

#0  g_type_check_instance (type_instance=0x100000001) at ../gobject/gtype.c:4257
#1  0x00007ffff6e8898c in g_signal_handlers_block_matched
    (instance=0x100000001, mask=mask@entry=(G_SIGNAL_MATCH_FUNC | G_SIGNAL_MATCH_DATA), signal_id=signal_id@entry=0, detail=detail@entry=0, closure=closure@entry=0x0, func=func@entry=0x7ffff70ae230 <_on_cfg_file_changed>, data=0x4bc930) at ../gobject/gsignal.c:2881
#2  0x00007ffff70a8296 in fm_config_save (cfg=0x4bc930, name=0x8eeb50 "/home/tasaka1/.config/libfm/libfm.conf", name@entry=0x0)
    at /usr/src/debug/libfm-1.3.2^20241216gitfb651b87-1.fc41.x86_64/libfm/_BUILDDIR_gtk3/../src/base/fm-config.c:487
#3  0x0000000000411f96 in pcmanfm_save_config (immediate=1)
    at /usr/src/debug/pcmanfm-1.3.2^20241203git836c77c8-1.fc41.x86_64/pcmanfm/src/pcmanfm.c:594
#4  on_save_config_idle (user_data=<optimized out>) at /usr/src/debug/pcmanfm-1.3.2^20241203git836c77c8-1.fc41.x86_64/pcmanfm/src/pcmanfm.c:585
#5  0x00007ffff7c2c00d in gdk_threads_dispatch (data=data@entry=0x8cc9a0) at ../gdk/gdk.c:769
#6  0x00007ffff6d5eadd in g_idle_dispatch (source=0x8f5550, callback=0x7ffff7c2bfe0 <gdk_threads_dispatch>, user_data=0x8cc9a0)
    at ../glib/gmain.c:6243
#7  0x00007ffff6d5828c in g_main_dispatch (context=0x48c420) at ../glib/gmain.c:3357
#8  g_main_context_dispatch_unlocked (context=0x48c420) at ../glib/gmain.c:4208
#9  0x00007ffff6db87b8 in g_main_context_iterate_unlocked.isra.0
    (context=0x48c420, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../glib/gmain.c:4273
#10 0x00007ffff6d5e377 in g_main_loop_run (loop=0x5b3cf0) at ../glib/gmain.c:4475
#11 0x00007ffff75efb35 in gtk_main () at ../gtk/gtkmain.c:1329
#12 0x0000000000407aab in main (argc=<optimized out>, argv=<optimized out>)
    at /usr/src/debug/pcmanfm-1.3.2^20241203git836c77c8-1.fc41.x86_64/pcmanfm/src/pcmanfm.c:284
(gdb) up

#1  0x00007ffff6e8898c in g_signal_handlers_block_matched (instance=0x100000001, mask=mask@entry=(G_SIGNAL_MATCH_FUNC | G_SIGNAL_MATCH_DATA), 
    signal_id=signal_id@entry=0, detail=detail@entry=0, closure=closure@entry=0x0, func=func@entry=0x7ffff70ae230 <_on_cfg_file_changed>, 
    data=0x4bc930) at ../gobject/gsignal.c:2881
2881      g_return_val_if_fail (G_TYPE_CHECK_INSTANCE (instance), 0);
(gdb) 

#2  0x00007ffff70a8296 in fm_config_save (cfg=0x4bc930, name=0x8eeb50 "/home/tasaka1/.config/libfm/libfm.conf", name@entry=0x0)
    at /usr/src/debug/libfm-1.3.2^20241216gitfb651b87-1.fc41.x86_64/libfm/_BUILDDIR_gtk3/../src/base/fm-config.c:487
487                 g_signal_handlers_block_by_func(cfg->_cfg_mon, _on_cfg_file_changed, cfg);
(gdb) p *cfg

$3 = {parent = {g_type_instance = {g_class = Python Exception <class 'gdb.error'>: value has been optimized out
}, ref_count = 2, qdata = 0x0}, _cfg_name = 0x4bcbf0 "libfm/libfm.conf", 
  terminal = 0x4cafd0 "lxterminal", archiver = 0x4cafb0 "file-roller", big_icon_size = 64, small_icon_size = 24, pane_icon_size = 24, 
  thumbnail_size = 128, thumbnail_max = 0, auto_selection_delay = 600, drop_default_action = 0, single_click = 0, middle_click = 0, 
  use_trash = 0, confirm_del = 1, confirm_trash = 1, show_thumbnail = 1, thumbnail_local = 0, show_internal_volumes = 0, si_unit = 0, 
  advanced_mode = 0, force_startup_notify = 1, date_iso_8601 = 0, backup_as_hidden = 1, no_usb_trash = 0, no_child_non_expandable = 0, 
  show_full_names = 1, shadow_hidden = 0, places_home = 1, places_desktop = 1, places_applications = 1, places_trash = 1, places_root = 0, 
  places_computer = 0, places_network = 0, places_unmounted = 1, only_user_templates = 0, template_run_app = 0, template_type_once = 0, 
  defer_content_test = 0, quick_exec = 0, modules_blacklist = 0x0, modules_whitelist = 0x0, system_modules_blacklist = 0x0, 
  list_view_size_units = 0x0, format_cmd = 0x0, smart_desktop_autodrop = 1, saved_search = 0x4bef10 "401/*54*/", _reserved1 = 0x0, 
  _reserved2 = 0x0, _reserved3 = 0x0, _reserved4 = 0x0, _reserved5 = 0x0, _reserved6 = 0x0, _reserved7 = 0x0, _cfg_mon = 0x100000001}
(gdb) quit

A debugging session is active.

        Inferior 1 [process 719630] will be killed.

Quit anyway? (y or n) quit

EOF [assumed Y]
[tasaka1@localhost ~]$ 

exit

[ib]

I'm afraid I was too hasty with your pull request and need to revert it and bump the major version of libfm instead. Otherwise, configuring date_iso_8601 won't work in pcmanfm.

Right now, pcmanfm is still safe because all uses of the new configuration settings are safeguarded with FM_CHECK_VERSION. But date_iso_8601, once available in libfm, will be read by INIT_BOOL_SHOW(builder, FmConfig, date_iso_8601, NULL) with gboolean* val = (gboolean*)G_STRUCT_MEMBER_P(fm_config, off) and *val which won't work with the definition of gintptr date_iso_8601 if gboolean is smaller than gintptr on big-endian.

[mtasaka]

Or create INIT_INTPTR or so. Otherwise struct _FmConfig have to have every bool reserved, int reserved type.

[mtasaka]

Or create INIT_FMCONFIG_WITH_SIZE with specifying size to read?

[ib]

INIT_FMCONFIG_WITH_SIZE

What you mean by that?

[ib]

The ABI remains stable with anonymous unions:

    union
    {
        gboolean date_iso_8601;
        gpointer _reserved1;
    };
    union
    {
        gboolean middle_click;
        gpointer _reserved2;
    };

Unless I missed something, this is how I'm going to fix #105.

[mtasaka]

INIT_FMCONFIG_WITH_SIZE

What you mean by that?

Currently INIT_BOOL or INIT_BOOL_SHOW cast a pointer by *gboolean and read it.
Instead, create go to a pointer and specify the size to read, something like:

static void init_bool(GtkBuilder* b, const char* name, gsize off,
                      const char* changed_notify, gboolean force_show,
                      gsize read_size
)
{
    GtkToggleButton* btn = GTK_TOGGLE_BUTTON(gtk_builder_get_object(b, name));
    gpointer* val = (gpointer*)G_STRUCT_MEMBER_P(fm_config, off);

    long value;
    switch (read_size) {
    case 1:
          int8_t val8;
          memcpy(&val8, val, 1);
         value = val8;
         break;
  case 2:
         int16_t val16;
         memcpy(&val16, val, 2);
        value = val16;
      break;
    ......
 }
}

[mtasaka]

But maybe the above method is overdone.

[mtasaka]

The ABI remains stable with anonymous unions:

    union
    {
        gboolean date_iso_8601;
        gpointer _reserved1;
    };
    union
    {
        gboolean middle_click;
        gpointer _reserved2;
    };

Unless I missed something, this is how I'm going to fix #105.

This seems reasonable to me.

[ib]

Applied.