[Bug gdb/34279] New: build failure on fedora rawhide x86-64 under clang: static_assert (sizeof (compat_x32_siginfo_t) == GDB_SI_SIZE);

https://sourceware.org/bugzilla/show_bug.cgi?id=34279

            Bug ID: 34279
           Summary: build failure on fedora rawhide x86-64 under clang:
                    static_assert (sizeof (compat_x32_siginfo_t) ==
                    GDB_SI_SIZE);
           Product: gdb
           Version: unknown
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
          Assignee: unassigned at sourceware dot org
          Reporter: fche at redhat dot com
  Target Milestone: ---

make[2]: Leaving directory
'/home/buildbot/buildbot/binutils-gdb-clang-fedrawhide-x86_64/build/gdb'
nat/amd64-linux-siginfo.c:610:16: error: static assertion failed due to
requirement 'sizeof(compat_x32_siginfo_t) == 128'
  610 | static_assert (sizeof (compat_x32_siginfo_t) == GDB_SI_SIZE);
      |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
nat/amd64-linux-siginfo.c:610:46: note: expression evaluates to '136 == 128'
  610 | static_assert (sizeof (compat_x32_siginfo_t) == GDB_SI_SIZE);
      |                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
1 error generated.

https://builder.sourceware.org/buildbot/#/builders/84/builds/5157/steps/3/logs/stdio


According to an ai speculation of the build logs, this may be likely due to
changes of clang versions:

The error was triggered by a compiler upgrade on the Fedora Rawhide buildbot
worker:
* **[Build
5155](https://builder.sourceware.org/testrun/432002d3102e15ef7f49e3f6e7cb0fc1bfb52180)**
(Completed successfully at 03:45 UTC) compiled with
`clang-22.1.6-6.fc45.x86_64`.
* **[Build
5156](https://builder.sourceware.org/testrun/6077e7a4f3cd813d13152111d4c227bf4a18c44d)**
(Started at 06:56 UTC) compiled with `clang-22.1.7-1.fc45.x86_64`.

The upgrade to **Clang 22.1.7** changed how the alignment attribute
`__attribute__ ((__aligned__ (4)))` is processed within aliases or structures,
resulting in different padding inside `compat_x32_siginfo_t` and increasing its
computed size from `128` bytes to `136` bytes.

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