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stefan11111
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PostPosted: Wed May 31, 2023 9:26 am    Post subject: COMMON_FLAGS="-nostdlib" Reply with quote

I have tried to build a patched version of atk with -nostdlib.
Code:
COMMON_FLAGS="-O2 -pipe -march=native -flto=4 -nostdlib"

However, when I do that I get:
Code:
../atk-2.38.0/meson.build:1:0: ERROR: Executables created by c compiler x86_64-pc-linux-gnu-gcc are not runnable.

Any ideas how to fix this?
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INSTALL_MASK="/etc/systemd /lib/systemd /usr/lib/systemd /usr/lib/modules-load.d *udev* /usr/lib/tmpfiles.d *tmpfiles* /var/lib/dbus /usr/bin/gdbus /lib/udev"
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GDH-gentoo
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PostPosted: Wed May 31, 2023 2:22 pm    Post subject: Re: COMMON_FLAGS="-nostdlib" Reply with quote

stefan11111 wrote:
Code:
../atk-2.38.0/meson.build:1:0: ERROR: Executables created by c compiler x86_64-pc-linux-gnu-gcc are not runnable.

That's expected. Option -nostdlib prevents linking by default to the libc, and to the system startup files (*crt*.o) and helper libraries like libgcc. Making the resulting executables essentially unusable on what the C and C++ standards call a "hosted environment".

What did you think that you needed -nostdlib for?
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NeddySeagoon wrote:
I'm not a witch, I'm a retired electronics engineer :)
Ionen wrote:
As a packager I just don't want things to get messier with weird build systems and multiple toolchains requirements though :)
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stefan11111
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PostPosted: Wed May 31, 2023 8:13 pm    Post subject: Re: COMMON_FLAGS="-nostdlib" Reply with quote

GDH-gentoo wrote:
stefan11111 wrote:
Code:
../atk-2.38.0/meson.build:1:0: ERROR: Executables created by c compiler x86_64-pc-linux-gnu-gcc are not runnable.

That's expected. Option -nostdlib prevents linking by default to the libc, and to the system startup files (*crt*.o) and helper libraries like libgcc. Making the resulting executables essentially unusable on what the C and C++ standards call a "hosted environment".

What did you think that you needed -nostdlib for?

The patch I linked strips atk to a couple of functions and typedefs. I don't want to link this against libc if I don't have too.
I've had success in the past with such approaches.
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INSTALL_MASK="/etc/systemd /lib/systemd /usr/lib/systemd /usr/lib/modules-load.d *udev* /usr/lib/tmpfiles.d *tmpfiles* /var/lib/dbus /usr/bin/gdbus /lib/udev"
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GDH-gentoo
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PostPosted: Wed May 31, 2023 9:38 pm    Post subject: Reply with quote

stefan11111 wrote:
I've had success in the past with such approaches.

It won't work if the build system tries to compile and run an executable with your supplied CFLAGS, as ATK's seemingly does. It works for your fake-libudev because its build system is just a makefile that doesn't try to run anything, it only builds a shared library that has no unresolved symbols.
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Ionen wrote:
As a packager I just don't want things to get messier with weird build systems and multiple toolchains requirements though :)
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pingtoo
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PostPosted: Thu Jun 01, 2023 12:24 am    Post subject: Reply with quote

stefan11111,

You may want to read about Hosted versus non-hosted (standalone) to understand what does it mean when using -nostdlib.
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stefan11111
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PostPosted: Wed Jun 07, 2023 10:14 am    Post subject: Reply with quote

I fixed the problem by replacing the meson build system with a Makefile. Seems nothing can beat that.
I changed the repo to this.

A comparison:
Code:
$ ls -lah /usr/lib64/libatk-1.0.so*
-rwxr-xr-x 1 root root 46K Jun  7 13:10 /usr/lib64/libatk-1.0.so
lrwxrwxrwx 1 root root  13 Jun  7 13:10 /usr/lib64/libatk-1.0.so.0 -> libatk-1.0.so
-rwxr-xr-x 1 root root 78K May 21 16:54 /usr/lib64/libatk-1.0.so.0.bak


Code:
$ objdump -d /usr/lib64/libatk-1.0.so | wc -l
1887
$ objdump -d /usr/lib64/libatk-1.0.so | wc -l
1887


Code:
$ ldd /usr/lib64/*atk*
/usr/lib64/libatk-1.0.so:
        statically linked
/usr/lib64/libatk-1.0.so.0:
        statically linked
/usr/lib64/libatk-1.0.so.0.bak:
        linux-vdso.so.1 (0x00007ffe2bfbc000)
        libglib-2.0.so.0 => /usr/lib64/libglib-2.0.so.0 (0x00007f93d5579000)
        libgobject-2.0.so.0 => /usr/lib64/libgobject-2.0.so.0 (0x00007f93d5518000)
        libpcre2-8.so.0 => /lib64/libpcre2-8.so.0 (0x00007f93d547c000)
        libc.so.6 => /lib64/libc.so.6 (0x00007f93d52a9000)
        libffi.so.8 => /usr/lib64/libffi.so.8 (0x00007f93d529e000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f93d56e0000)


I also added an ebuild for it to my overlay.
When I emerge it, I get a warning I don't get if I emerge fake-libudev.
Code:
 * QA Notice: The following shared libraries lack NEEDED entries
 * /usr/lib64/libatk-1.0.so

Any idea how to fix this?
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GDH-gentoo
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PostPosted: Wed Jun 07, 2023 12:53 pm    Post subject: Reply with quote

stefan11111 wrote:
When I emerge it, I get a warning I don't get if I emerge fake-libudev.
Code:
 * QA Notice: The following shared libraries lack NEEDED entries
 * /usr/lib64/libatk-1.0.so

Any idea how to fix this?

That's a Portage QA check, post the output of nm -D /usr/lib64/libatk-1.0.so.0. For your modified libatk, obviously.
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NeddySeagoon wrote:
I'm not a witch, I'm a retired electronics engineer :)
Ionen wrote:
As a packager I just don't want things to get messier with weird build systems and multiple toolchains requirements though :)
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stefan11111
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PostPosted: Wed Jun 07, 2023 6:49 pm    Post subject: Reply with quote

GDH-gentoo wrote:
stefan11111 wrote:
When I emerge it, I get a warning I don't get if I emerge fake-libudev.
Code:
 * QA Notice: The following shared libraries lack NEEDED entries
 * /usr/lib64/libatk-1.0.so

Any idea how to fix this?

That's a Portage QA check, post the output of nm -D /usr/lib64/libatk-1.0.so.0. For your modified libatk, obviously.

Code:
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                 U g_boxed_type_register_static
                 U g_cclosure_marshal_VOID__BOOLEAN
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                 U g_cclosure_marshal_VOID__UINT_POINTER
                 U g_cclosure_marshal_VOID__VOID
                 U g_dgettext
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                 U g_intern_static_string
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                 U g_param_spec_string
                 U g_return_if_fail_warning
                 U g_signal_new
                 U g_type_add_instance_private
                 U g_type_check_instance_is_a
                 U g_type_class_adjust_private_offset
                 U g_type_class_peek_parent
                 U g_type_interface_add_prerequisite
                 U g_type_register_static
                 U g_type_register_static_simple

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PostPosted: Wed Jun 07, 2023 7:03 pm    Post subject: Reply with quote

stefan11111 wrote:
Code:
                 U g_boxed_type_register_static
                 U g_cclosure_marshal_VOID__BOOLEAN
                 U g_cclosure_marshal_VOID__POINTER
                 U g_cclosure_marshal_VOID__UINT_POINTER
                 U g_cclosure_marshal_VOID__VOID
                 U g_dgettext
                 ...
                 U g_intern_static_string
                 U g_object_class_install_property
                 U g_once_init_enter
                 U g_once_init_leave
                 U g_param_spec_double
                 U g_param_spec_enum
                 U g_param_spec_int
                 U g_param_spec_object
                 U g_param_spec_string
                 U g_return_if_fail_warning
                 U g_signal_new
                 U g_type_add_instance_private
                 U g_type_check_instance_is_a
                 U g_type_class_adjust_private_offset
                 U g_type_class_peek_parent
                 U g_type_interface_add_prerequisite
                 U g_type_register_static
                 U g_type_register_static_simple

You have undefined symbols; your modified code must still have references to those functions / objects / whatever they are (from GLib maybe?).
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PostPosted: Wed Jun 07, 2023 7:11 pm    Post subject: Reply with quote

GDH-gentoo wrote:

You have undefined symbols; your modified code must still have references to those functions / objects / whatever they are (from GLib maybe?).

You mean the U 's?
The unmodified atk has plenty of those too.
Code:
                 w __cxa_finalize@GLIBC_2.2.5
                 U dcgettext@GLIBC_2.2.5
                 U g_array_append_vals
                 U g_array_remove_index
                 U g_array_sized_new
                 U g_assertion_message_expr
                 U g_boxed_type_register_static
                 U g_cclosure_marshal_VOID__BOOLEAN
                 U g_cclosure_marshal_VOID__BOXED
                 U g_cclosure_marshal_VOID__INT
                 U g_cclosure_marshal_VOID__POINTER
                 U g_cclosure_marshal_VOID__UINT_POINTER
                 U g_cclosure_marshal_VOID__VOID
                 U g_dgettext
                 U g_enum_get_value
                 U g_enum_get_value_by_nick
                 U g_enum_register_static
                 U g_flags_register_static
                 U g_free
                 U g_hash_table_destroy
                 U g_hash_table_insert
                 U g_hash_table_lookup
                 U g_hash_table_new
                 U g_hash_table_new_full
                 U g_hash_table_remove
                 U g_int_equal
                 U g_intern_static_string
                 U g_int_hash
                 U g_log_structured_standard
                 U g_malloc
                 U g_malloc0
                 w __gmon_start__
                 U g_object_class_install_property
                 U g_object_get_property
                 U g_object_get_qdata
                 U g_object_new
                 U g_object_notify
                 U g_object_ref
                 U g_object_set_qdata
                 U g_object_unref
                 U g_object_weak_ref
                 U g_object_weak_unref
                 U g_once_init_enter
                 U g_once_init_leave
                 U g_param_spec_boolean
                 U g_param_spec_double
                 U g_param_spec_enum
                 U g_param_spec_int
                 U g_param_spec_object
                 U g_param_spec_string
                 U g_param_spec_value_array
                 U g_ptr_array_add
                 U g_ptr_array_free
                 U g_ptr_array_new
                 U g_ptr_array_remove
                 U g_ptr_array_sized_new
                 U g_quark_from_static_string
                 U g_quark_from_string
                 U g_realloc
                 U g_return_if_fail_warning
                 U g_signal_add_emission_hook
                 U g_signal_emit
                 U g_signal_lookup
                 U g_signal_new
                 U g_signal_remove_emission_hook
                 U g_slice_alloc
                 U g_slice_free1
                 U g_slist_free
                 U g_strdup
                 U g_strfreev
                 U g_strsplit
                 U g_strv_length
                 U g_type_add_instance_private
                 U g_type_add_interface_static
                 U g_type_check_class_is_a
                 U g_type_check_instance_is_a
                 U g_type_check_instance_is_fundamentally_a
                 U g_type_check_value
                 U g_type_class_adjust_private_offset
                 U g_type_class_peek
                 U g_type_class_peek_parent
                 U g_type_class_ref
                 U g_type_class_unref
                 U g_type_create_instance
                 U g_type_free_instance
                 U g_type_from_name
                 U g_type_interface_add_prerequisite
                 U g_type_interface_peek
                 U g_type_name
                 U g_type_parent
                 U g_type_register_static
                 U g_type_register_static_simple
                 U g_utf8_strlen
                 U g_value_array_append
                 U g_value_array_free
                 U g_value_array_get_nth
                 U g_value_array_new
                 U g_value_get_boxed
                 U g_value_get_enum
                 U g_value_get_object
                 U g_value_get_string
                 U g_value_init
                 U g_value_peek_pointer
                 U g_value_set_boolean
                 U g_value_set_boxed
                 U g_value_set_enum
                 U g_value_set_int
                 U g_value_set_object
                 U g_value_set_string
                 U g_value_unset
                 w _ITM_deregisterTMCloneTable
                 w _ITM_registerTMCloneTable
                 U setlocale@GLIBC_2.2.5
                 U __stack_chk_fail@GLIBC_2.4
                 U strcmp@GLIBC_2.2.5

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PostPosted: Wed Jun 07, 2023 7:20 pm    Post subject: Reply with quote

stefan11111 wrote:
You mean the U 's?

Yup.

stefan11111 wrote:
The unmodified atk has plenty of those too.

It has more, but more importantly, it specifies the set of shared libraries that should provide corresponding definitions because it was properly linked:

stefan11111 wrote:
Code:
/usr/lib64/libatk-1.0.so.0.bak:
        linux-vdso.so.1 (0x00007ffe2bfbc000)
        libglib-2.0.so.0 => /usr/lib64/libglib-2.0.so.0 (0x00007f93d5579000)
        libgobject-2.0.so.0 => /usr/lib64/libgobject-2.0.so.0 (0x00007f93d5518000)
        libpcre2-8.so.0 => /lib64/libpcre2-8.so.0 (0x00007f93d547c000)
        libc.so.6 => /lib64/libc.so.6 (0x00007f93d52a9000)
        libffi.so.8 => /usr/lib64/libffi.so.8 (0x00007f93d529e000)
        /lib64/ld-linux-x86-64.so.2 (0x00007f93d56e0000)

If you are going to use -nostdlib, you can't have undefined symbols. Not a single one.
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PostPosted: Wed Jun 07, 2023 9:47 pm    Post subject: Reply with quote

Shouldn't those undefined symbols cause a linker error when building the shared library?
If I try to build something like this:
Code:
void main()
{
    __asm__(".globl _start\n"
            "_start:"
           );
    printf("Hello world!\n");
}

It fails with a linker error:
Code:
/usr/lib/gcc/x86_64-pc-linux-gnu/13/../../../../x86_64-pc-linux-gnu/bin/ld: /tmp/cc3S4PKG.o: in function `_start':
ttt.c:(.text+0xf): undefined reference to `puts'
collect2: error: ld returned 1 exit status


What is going to happen if one of those undefined symbols gets called? Segfault?
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PostPosted: Wed Jun 07, 2023 10:12 pm    Post subject: Reply with quote

Undefined symbols in a shared library may or may not be fatal at link time, depending on whether the linker was told to make them fatal. If not fatal at link time, then they will be fatal at resolution time if no defined symbol can be found for them.
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PostPosted: Wed Jun 07, 2023 11:32 pm    Post subject: Reply with quote

stefan11111 wrote:
What is going to happen if one of those undefined symbols gets called? Segfault?

What Hu said. A link failure.

I did some tests with GCC. It will let you create a shared library without complaints:

Code:
$ cat test1.c
int some_other_function(void);

int some_function() {
   return some_other_function();
}

$ gcc -fPIC -shared -Wl,-soname=test.so -nostdlib -o test.so test1.c && echo No problems here
No problems here

$ objdump -p test.so

test.so:     file format elf64-x86-64

Program Header:
...

Dynamic Section:
  SONAME               test.so
  GNU_HASH             0x0000000000000270
  STRTAB               0x00000000000002e0
  SYMTAB               0x0000000000000298
  STRSZ                0x000000000000002b
  SYMENT               0x0000000000000018
  PLTGOT               0x0000000000004000
  PLTRELSZ             0x0000000000000018
  PLTREL               0x0000000000000007
  JMPREL               0x0000000000000310

$ nm -D test.so
0000000000001020 T some_function
                 U some_other_function

It won't let you create an executable linked to such a library.

Code:
$ cat test2.c
int some_function(void);

int main() {
   return some_function();
}

$ gcc -o test test2.c test.so
/usr/bin/ld: test.so: undefined reference to `some_other_function'
collect2: error: ld returned 1 exit status

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PostPosted: Wed Jun 14, 2023 10:59 am    Post subject: Reply with quote

I looked a bit into different compiler optimization levels:
Here is what one empty function looks like.
With -O1, it produces this code, which is inefficient:
Code:
    5090:       b8 00 00 00 00          mov    $0x0,%eax
    5095:       c3                      ret

With -Os, it produces the xor(efficient) version of this:
Code:
    5090:       31 c0                   xor    %eax,%eax
    5092:       c3                      ret

With -O2, -O3 and -Ofast, it adds some more stuff which I have no idea what it does:
Code:
    5090:       31 c0                   xor    %eax,%eax
    5092:       c3                      ret
    5093:       66 66 2e 0f 1f 84 00    data16 cs nopw 0x0(%rax,%rax,1)
    509a:       00 00 00 00
    509e:       66 90                   xchg   %ax,%ax

What's this about? Also, isn't everything after ret ignored?

Also, I removed most of the undefined symbols.
These are the one I am left with as of now:
Code:
                 U g_object_class_install_property
                 U g_param_spec_object
                 U g_param_spec_string
                 U g_type_add_instance_private
                 U g_type_class_adjust_private_offset
                 U g_type_class_peek_parent
                 U g_type_register_static

If I leave them undefined and just live with that emerge warning, will there be any problems?
If programs will just fail with a linker warning if they are not linked against glib, there is no way to introduce other problems, like segfaults and security vulnerabilities.
It seems like the useful part of atk can be reduced to:
Code:
static void bloat()
{
}

long unsigned int
atk_object_get_type (void)
{
  static long unsigned int type = 0;

  if (!type)
    {
      static const GTypeInfo typeInfo =
      {
        sizeof (AtkObjectClass),
        0,
        0,
        atk_object_class_init,
        0,
        0,
        sizeof (AtkObject),
        0,
        bloat,
      } ;
      type = g_type_register_static (G_TYPE_OBJECT, "AtkObject", &typeInfo, 0) ;

      AtkObject_private_offset =
        g_type_add_instance_private (type, sizeof (AtkObjectPrivate));
    }
  return type;
}

static inline void*
atk_object_get_instance_private (AtkObject *self)
{
  return (G_STRUCT_MEMBER_P (self, AtkObject_private_offset));
}

static void
atk_object_class_init (AtkObjectClass *klass)
{
  GObjectClass *gobject_class = G_OBJECT_CLASS (klass);

  parent_class = g_type_class_peek_parent (klass);

  if (AtkObject_private_offset != 0)
    g_type_class_adjust_private_offset (klass, &AtkObject_private_offset);

  gobject_class->set_property = bloat;
  gobject_class->get_property = bloat;
  gobject_class->finalize = bloat;
  gobject_class->notify = bloat;

  klass->get_name = bloat;
  klass->get_description = bloat;
  klass->get_parent = bloat;
  klass->get_n_children = 0;
  klass->ref_child = 0;
  klass->get_index_in_parent = 0;
  klass->ref_relation_set = bloat;
  klass->get_role = bloat;
  klass->get_layer = bloat;
  klass->get_mdi_zorder = 0;
  klass->initialize = bloat;
  klass->ref_state_set = bloat;
  klass->set_name = bloat;
  klass->set_description = bloat;
  klass->set_parent = bloat;
  klass->set_role = bloat;
  klass->get_object_locale = bloat;

  /*
   * We do not define default signal handlers here
   */
  klass->children_changed = 0;
  klass->focus_event = 0;
  klass->property_change = 0;
  klass->visible_data_changed = 0;
  klass->active_descendant_changed = 0;

  g_object_class_install_property (gobject_class,
                                   PROP_NAME,
                                   g_param_spec_string (atk_object_name_property_name,
                                                        0,
                                                        0,
                                                        0,
                                                        G_PARAM_READWRITE));
  g_object_class_install_property (gobject_class,
                                   PROP_PARENT,
                                   g_param_spec_object (atk_object_name_property_parent,
                                                        0,
                                                        0,
                                                        ATK_TYPE_OBJECT,
                                                        G_PARAM_READWRITE));
}

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PostPosted: Thu Jun 15, 2023 9:37 am    Post subject: Reply with quote

stefan11111 wrote:
I If I leave them undefined and just live with that emerge warning, will there be any problems?

Yes, see posts above yours.

stefan11111 wrote:
If programs will just fail with a linker warning if they are not linked against glib, there is no way to introduce other problems, like segfaults and security vulnerabilities.

Not warning, fatal failure. The build is aborted and you end up with no program at all.

stefan11111 wrote:
It seems like the useful part of atk can be reduced to:
Code:
...

Yeah. bloat() contains the important part :-P
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PostPosted: Thu Jun 15, 2023 11:49 am    Post subject: Reply with quote

The more I look into Glib, the more I hate it:
Code:
struct  _GObjectClass
{
  GTypeClass   g_type_class;

  /*< private >*/
  GSList      *construct_properties;

  /*< public >*/
  /* seldom overridden */
  GObject*   (*constructor)     (GType                  type,
                                 guint                  n_construct_properties,
                                 GObjectConstructParam *construct_properties);
  /* overridable methods */
  void       (*set_property)            (GObject        *object,
                                         guint           property_id,
                                         const GValue   *value,
                                         GParamSpec     *pspec);
  void       (*get_property)            (GObject        *object,
                                         guint           property_id,
                                         GValue         *value,
                                         GParamSpec     *pspec);
  void       (*dispose)                 (GObject        *object);
  void       (*finalize)                (GObject        *object);
  /* seldom overridden */
  void       (*dispatch_properties_changed) (GObject      *object,
                                             guint         n_pspecs,
                                             GParamSpec  **pspecs);
  /* signals */
  void       (*notify)                  (GObject        *object,
                                         GParamSpec     *pspec);

  /* called when done constructing */
  void       (*constructed)             (GObject        *object);

  /*< private >*/
  gsize         flags;

  gsize         n_construct_properties;

  gpointer pspecs;
  gsize n_pspecs;

  /* padding */
  gpointer      pdummy[3];
};

Code:
typedef struct _GTypeClass              GTypeClass;

Code:
struct _GTypeClass
{
  /*< private >*/
  GType g_type;
};

Code:
typedef gsize GType;

Code:
typedef unsigned long gsize;

So GObjectClass is struct _GObjectClass which has a member of type GTypeClass which is struct _GTypeClass which only has a member of type GType which is gsize which is unsigned long.
Why?
Why everything is scattered across so many files with so many levels of opacity?
Why does that struct have 3 pointer of padding? It's not like when people add char[n] to make use of padding that is already there. This is just there to waste memory.
Why do we need a typedef for a struct with a single member?
And worst of all, why do this travesty with function pointers? What is wrong with having functions and structs separate?
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GDH-gentoo
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PostPosted: Thu Jun 15, 2023 2:51 pm    Post subject: Reply with quote

stefan11111 wrote:
Why?
Why everything is scattered across so many files with so many levels of opacity?
Why does that struct have 3 pointer of padding? It's not like when people add char[n] to make use of padding that is already there. This is just there to waste memory.
Why do we need a typedef for a struct with a single member?
And worst of all, why do this travesty with function pointers? What is wrong with having functions and structs separate?

That's how object-oriented programming style in a language that doesn't support it natively ends up looking like. It's support for classes and objects of class types 'hand-compiled' by a programmer to something that can be expressed in C.
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PostPosted: Thu Jun 15, 2023 3:22 pm    Post subject: Reply with quote

GDH-gentoo wrote:
stefan11111 wrote:
Why?
Why everything is scattered across so many files with so many levels of opacity?
Why does that struct have 3 pointer of padding? It's not like when people add char[n] to make use of padding that is already there. This is just there to waste memory.
Why do we need a typedef for a struct with a single member?
And worst of all, why do this travesty with function pointers? What is wrong with having functions and structs separate?

That's how object-oriented programming style in a language that doesn't support it natively ends up looking like. It's support for classes and objects of class types 'hand-compiled' by a programmer to something that can be expressed in C.

That explains the function pointers, but why the typedefs? Why the extra 3 pointers of wasted space? Why all the wasted space? You don't need so much space and so many types.
Code:
typedef gint   gboolean;

Why waste 4 bytes on a bool? Why define all these new types? What did the standard ones not accomplish?
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sMueggli
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PostPosted: Thu Jun 15, 2023 4:00 pm    Post subject: Reply with quote

stefan11111 wrote:

Code:
typedef gint   gboolean;

Why waste 4 bytes on a bool? Why define all these new types? What did the standard ones not accomplish?


Why do you think, that 4 bytes are wasted for a bool? On a x86_64 system, the cpu register has a size of 64 bits and 4 bytes occupy only 32 bit (if one byte is defined as 8 bit).

I guess it is easier to change typedefs in a project.

And what are "the standard ones" for you?
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PostPosted: Thu Jun 15, 2023 4:03 pm    Post subject: Reply with quote

glib also predates C99. They're working on moving to standard types too (https://gitlab.gnome.org/GNOME/glib/-/issues/1484). _Bool vs int can also affect ABI.
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PostPosted: Thu Jun 15, 2023 4:51 pm    Post subject: Reply with quote

sMueggli wrote:
stefan11111 wrote:

Code:
typedef gint   gboolean;

Why waste 4 bytes on a bool? Why define all these new types? What did the standard ones not accomplish?


Why do you think, that 4 bytes are wasted for a bool? On a x86_64 system, the cpu register has a size of 64 bits and 4 bytes occupy only 32 bit (if one byte is defined as 8 bit).

Try it on x86_64:
Code:
int main() {
    printf("%d\n", sizeof(int));
    return 0;
}


gint is a int, not a pointer;
sMueggli wrote:

And what are "the standard ones" for you?

These:
https://en.wikipedia.org/wiki/C_data_types
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PostPosted: Fri Jun 16, 2023 9:57 am    Post subject: Reply with quote

Ok, I was digging a bit deeper.

With the Makefile
Code:
all: booleans_bin booleans_opt

booleans_bin: booleans.c
   gcc -o booleans -Wall -Wpedantic booleans.c

booleans_opt: booleans.c
   gcc -o booleans_opt -Wall -Wpedantic -O3 booleans.c

clean:
   rm -rf *.o *~


and the code
Code:
#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>

int main(int argc, char* argv[]) {

  typedef int gint;
  typedef gint gboolean;

  bool stdbool = 2 == argc;
  gboolean glibbool = 3 == argc;

  if (stdbool) {
    puts("2");
  }

  if (glibbool) {
    puts("3");
  }

  return EXIT_SUCCESS;
}


Using radare2 resulted in
Code:
            ; DATA XREF from entry0 @ 0x1064(r)
┌ 87: int main (uint32_t argc, char **argv);
│           ; arg uint32_t argc @ rdi
│           ; arg char **argv @ rsi
│           ; var uint32_t var_4h @ rbp-0x4
│           ; var uint32_t var_5h @ rbp-0x5
│           ; var uint32_t var_14h @ rbp-0x14
│           ; var char **var_20h @ rbp-0x20
│           0x00001165      55             push rbp
│           0x00001166      4889e5         mov rbp, rsp
│           0x00001169      4883ec20       sub rsp, 0x20
│           0x0000116d      897dec         mov dword [var_14h], edi    ; argc
│           0x00001170      488975e0       mov qword [var_20h], rsi    ; argv
│           0x00001174      837dec02       cmp dword [var_14h], 2
│           0x00001178      0f94c0         sete al
│           0x0000117b      8845fb         mov byte [var_5h], al
│           0x0000117e      837dec03       cmp dword [var_14h], 3
│           0x00001182      0f94c0         sete al
│           0x00001185      0fb6c0         movzx eax, al
│           0x00001188      8945fc         mov dword [var_4h], eax
│           0x0000118b      807dfb00       cmp byte [var_5h], 0
│       ┌─< 0x0000118f      740f           je 0x11a0
│       │   0x00001191      488d056c0e00.  lea rax, [0x00002004]       ; u"23\u1b01\u3b03,"
│       │   0x00001198      4889c7         mov rdi, rax                ; const char *s
│       │   0x0000119b      e890feffff     call sym.imp.puts           ; int puts(const char *s)
│       │   ; CODE XREF from main @ 0x118f(x)
│       └─> 0x000011a0      837dfc00       cmp dword [var_4h], 0
│       ┌─< 0x000011a4      740f           je 0x11b5
│       │   0x000011a6      488d05590e00.  lea rax, [0x00002006]       ; "3"
│       │   0x000011ad      4889c7         mov rdi, rax                ; const char *s
│       │   0x000011b0      e87bfeffff     call sym.imp.puts           ; int puts(const char *s)
│       │   ; CODE XREF from main @ 0x11a4(x)
│       └─> 0x000011b5      b800000000     mov eax, 0
│           0x000011ba      c9             leave
└           0x000011bb      c3             ret


and
Code:
            ;-- section..text:
            ; DATA XREF from entry0 @ 0x10a4(r)
┌ 49: int main (uint32_t argc);
│           ; arg uint32_t argc @ rdi
│           0x00001050      4883ec08       sub rsp, 8                  ; [14] -r-x section size 341 named .text
│           0x00001054      83ff02         cmp edi, 2                  ; argc
│       ┌─< 0x00001057      740c           je 0x1065
│       │   0x00001059      83ff03         cmp edi, 3                  ; argc
│      ┌──< 0x0000105c      7415           je 0x1073
│      ││   ; CODE XREFS from main @ 0x1071(x), 0x107f(x)
│    ┌┌───> 0x0000105e      31c0           xor eax, eax
│    ╎╎││   0x00001060      4883c408       add rsp, 8
│    ╎╎││   0x00001064      c3             ret
│    ╎╎││   ; CODE XREF from main @ 0x1057(x)
│    ╎╎│└─> 0x00001065      488d3d980f00.  lea rdi, [0x00002004]       ; u"23\u1b01\u3b03," ; const char *s
│    ╎╎│    0x0000106c      e8bfffffff     call sym.imp.puts           ; int puts(const char *s)
│    └────< 0x00001071      ebeb           jmp 0x105e
│     ╎│    ; CODE XREF from main @ 0x105c(x)
│     ╎└──> 0x00001073      488d3d8c0f00.  lea rdi, [0x00002006]       ; "3" ; const char *s
│     ╎     0x0000107a      e8b1ffffff     call sym.imp.puts           ; int puts(const char *s)
└     └───< 0x0000107f      ebdd           jmp 0x105e


And indeed, the "normal" compiled binary contains one instruction more for the "gboolean" part:
Code:
0x00001185      0fb6c0         movzx eax, al

I am not sure, but I guess, the performance of "mov byte trgt, src" and "mov dword trgt,src" is the same.

The "optimised" binary though does not contain a trace of the local variables. So there is no waste of "bytes".
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PostPosted: Fri Jun 16, 2023 10:26 am    Post subject: Reply with quote

Yours is a very specific use case of gboolean.
I can live with 3 bytes of wasted memory.
but what if I create a struct with a few gboolean members? Maybe a linked list with such elements.
It's not just about 3 bytes. They add up.

And also, why those 3 pointers of padding in struct _GObjectClass?
Those aren't three bytes, on amd64 those are 24 bytes for each GObjectClass element. That really adds up. and it's a waste of space.
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PostPosted: Fri Jun 16, 2023 1:27 pm    Post subject: Reply with quote

stefan11111 wrote:
Yours is a very specific use case of gboolean.

Yes, indeed.

stefan11111 wrote:

I can live with 3 bytes of wasted memory.
but what if I create a struct with a few gboolean members? Maybe a linked list with such elements.
It's not just about 3 bytes. They add up.


If you are creating a struct, you are also responsible for the memory layout/alignment. If you take gbooleans, you might have your reasons (readability, ease of maintenance...). But you can also choose another approach which is more "resource-friendly" in one or another way.

Depending on the elements and the order, a struct may use more space due to padding.

stefan11111 wrote:

And also, why those 3 pointers of padding in struct _GObjectClass?
Those aren't three bytes, on amd64 those are 24 bytes for each GObjectClass element. That really adds up. and it's a waste of space.


I am not a C programmer and also not using glib. So I do not have any practical experience in this regard.
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