[Bug gdb/30547] [gdb, s390x, ppc64] segfault in for_each_block

["cvs-commit at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30547

--- Comment #9 from Sourceware Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tom de Vries <vries@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=14414227bfac8ef1803715b3b642f8ba0ab6fff8

commit 14414227bfac8ef1803715b3b642f8ba0ab6fff8
Author: Tom de Vries <tdevries@suse.de>
Date:   Tue Nov 28 10:31:25 2023 +0100

    [gdb] Fix segfault in for_each_block, part 2

    The previous commit describes PR gdb/30547, a segfault when running
test-case
    gdb.base/vfork-follow-parent.exp on powerpc64 (likewise on s390x).

    The root cause for the segmentation fault is that linux_is_uclinux gives an
    incorrect result: it returns true instead of false.

    So, why does linux_is_uclinux:
    ...
    int
    linux_is_uclinux (void)
    {
      CORE_ADDR dummy;

      return (target_auxv_search (AT_NULL, &dummy) > 0
              && target_auxv_search (AT_PAGESZ, &dummy) == 0);
    ...
    return true?

    This is because ppc_linux_target_wordsize returns 4 instead of 8, causing
    ppc_linux_nat_target::auxv_parse to misinterpret the auxv vector.

    So, why does ppc_linux_target_wordsize:
    ...
    int
    ppc_linux_target_wordsize (int tid)
    {
      int wordsize = 4;

      /* Check for 64-bit inferior process.  This is the case when the host is
         64-bit, and in addition the top bit of the MSR register is set.  */
      long msr;

      errno = 0;
      msr = (long) ptrace (PTRACE_PEEKUSER, tid, PT_MSR * 8, 0);
      if (errno == 0 && ppc64_64bit_inferior_p (msr))
        wordsize = 8;

      return wordsize;
    }
    ...
    return 4?

    Specifically, we get this result because because tid == 0, so we get
    errno == ESRCH.

    The tid == 0 is caused by the switch_to_no_thread in
    handle_vfork_child_exec_or_exit:
    ...
              /* Switch to no-thread while running clone_program_space, so
                 that clone_program_space doesn't want to read the
                 selected frame of a dead process.  */
              scoped_restore_current_thread restore_thread;
              switch_to_no_thread ();

              inf->pspace = new program_space (maybe_new_address_space ());
    ...
    but moving the maybe_new_address_space call to before that gives us the
    same result.  The tid is no longer 0, but we still get ESRCH because the
    thread has exited.

    Fix this in handle_vfork_child_exec_or_exit by doing the
    maybe_new_address_space call in the context of the vfork parent.

    Tested on top of trunk on x86_64-linux and ppc64le-linux.
    Tested on top of gdb-14-branch on ppc64-linux.

    Co-Authored-By: Simon Marchi <simon.marchi@polymtl.ca>

    PR gdb/30547
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30547

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