update info on the segfault on RHEL

	/* show panel, wait 3s, then hide panel and exit app */

	err = NULL;

	const gchar *const candidates[] = {"第一个", "第二个", "第三个"};

	/* g_message("first: %s", candidates[0]); */

	GVariant *hints = NULL;

	GVariantBuilder b = {0};

	g_variant_builder_init(&b, G_VARIANT_TYPE("a{sv}"));

* current                                                             :entry:

** 

** 2023-08-16 bug: ./build/zero-panel-client-demo segfault on RHEL9.

** 2023-08-16 bug: ./build/zero-panel-client-demo with -O2 segfault on RHEL9.

- it runs fine on lat21. but has a few warnings. fix the warnings.

  #+BEGIN_SRC sh

    sylecn@lat21:~/projects/zero-panel$ ./build/zero-panel-client-demo

    ,** Message: 12:11:41.111: call Hide() okay

    ,** Message: 12:11:41.111: shutdown()

  #+END_SRC

- search: GLib-CRITICAL assert how to debug get source code line?

  rm -rf build/

  env G_DEBUG=fatal-criticals ./build/zero-panel-client-demo

- I think the Chinese char* literal is most suspicious.

- INVALID I think the Chinese char* literal is most suspicious.

  try use ascii string there.

  yes. debugoptimized build warning is gone when only use ascii string.

  all char* is assumed to be utf-8. it is supported out of the box.

- I got a minimal reproducible demo.

  // segfault also happen in -O2 with ascii literal. it's not utf-8 string

  issue.

- FIXED I got a minimal reproducible demo. // this is another locale issue. fixed.

  #+BEGIN_SRC c

    const gchar* first = "第一个";

    g_assert_true(g_utf8_validate(first, -1, NULL));

  // good.

- warning still persist after adding setlocale() call.

  new code still segfault on RHEL9.

  on RHEL9,

  debug build doesn't segfault.

  has a warning.

  #+BEGIN_SRC sh

    ,** (zero-panel-client-demo:36293): WARNING **: 14:43:15.167: call ShowCandidates() failed: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name is not activatable

  #+END_SRC

  the demo requires zero-panel service running.

  when zero-panel service is running. the program in debug mode runs fine in

  RHEL9.

  debugoptimized still segfault.

  #+BEGIN_SRC sh

    or help, type "help".

    Type "apropos word" to search for commands related to "word"...

    Reading symbols from ./build/zero-panel-client-demo...

    (gdb) run

    Starting program: /home/sylecn/fromsource/zero-panel/build/zero-panel-client-demo 

    [Thread debugging using libthread_db enabled]

    Using host libthread_db library "/lib64/libthread_db.so.1".

    [New Thread 0x7fffea1ff640 (LWP 37881)]

    [New Thread 0x7fffe99fe640 (LWP 37882)]

    Thread 1 "zero-panel-clie" received signal SIGSEGV, Segmentation fault.

    0x00007ffff7cce680 in g_utf8_validate () from /lib64/libglib-2.0.so.0

    Missing separate debuginfos, use: dnf debuginfo-install glib2-2.68.4-6.el9.x86_64 glibc-2.34-60.el9.x86_64 libblkid-2.37.4-11.el9_2.x86_64 libffi-3.4.2-7.el9.x86_64 libmount-2.37.4-11.el9_2.x86_64 libselinux-3.5-1.el9.x86_64 pcre-8.44-3.el9.3.x86_64 pcre2-10.40-2.el9.x86_64

    (gdb) 

  #+END_SRC

  sudo dnf debuginfo-install glib2-2.68.4-6.el9.x86_64 glibc-2.34-60.el9.x86_64 \

    libblkid-2.37.4-11.el9_2.x86_64 libffi-3.4.2-7.el9.x86_64 \

    libmount-2.37.4-11.el9_2.x86_64 libselinux-3.5-1.el9.x86_64 \

    pcre-8.44-3.el9.3.x86_64 pcre2-10.40-2.el9.x86_64 \

    zlib-1.2.11-39.el9.x86_64

- gdb show error is in

  0x00007ffff7cce680 in g_utf8_validate () from /lib64/libglib-2.0.so.0

  #+BEGIN_SRC sh

    Thread 1 "zero-panel-clie" received signal SIGSEGV, Segmentation fault.

    g_utf8_validate (str=0x1 <error: Cannot access memory at address 0x1>, 

	max_len=-1, end=0x0) at ../glib/gutf8.c:1671

    1671	g_utf8_validate (const char   *str,

  #+END_SRC

  now this is clear.

  str=0x1 <error: Cannot access memory at address 0x1>

  0x1 doesn't look like a proper memory address.

  C Language, cannot access memory at 0x1

  http://computer-programming-forum.com/17-c-language/91171078d803c0ab.htm

  #+begin_quote

  Almost certainly an uninitialised pointer

  #+end_quote

  #+begin_quote

  The usual cause of this type of problem is misusing, or abusing, a pointer.

  #+end_quote

  on rh901, in build/ dir.

  meson configure --optimization=1

  no error when running ./build/zero-panel-client-demo

  unicode literal in source code is no issue.

  meson configure --optimization=2

  segfault.

  confirmed it's gcc optimization issue.

  my code has problem when compiled with gcc -O2.

  c - signal SIGSEGV caused by the -O2 flag - Stack Overflow

  https://stackoverflow.com/questions/70629842/signal-sigsegv-caused-by-the-o2-flag

  debugging - What are best practices for finding a bug in a C program that only shows up in optimized build - Stack Overflow

  https://stackoverflow.com/questions/6455347/what-are-best-practices-for-finding-a-bug-in-a-c-program-that-only-shows-up-in-o

  valgrind

  just use valgrind to run it on lat21. it will reveal the problem.

- use valgrind to find bugs.

  ==9852==    by 0x10BF77: zero_panel_call_show_candidates_sync (zero-panel-generated-fixed.c:901)

  I can't see what's wrong there.

  all passed in arguments are initialized.

- problems

  - I can't install valgrind on rh901. license issue.

    VM is not registered properly.

** 2023-08-16 what's new in gtk4? should I upgrade?

- Gtk – 4.0: Migrating from GTK 3.x to GTK 4