Re: [RFA 3/5 v2] Darwin: set startup-with-shell to off on Sierra and later.

[Simon Marchi <simon.marchi@polymtl.ca>]

Thanks for the update!

CCing Tom, because he had a similar patch that was unfortunately not 
looked at yet... so maybe he has an opinion about this.

On 2018-09-09 11:17, Xavier Roirand wrote:
> On Mac OS X Sierra and later, the shell is not allowed to be
> debug so add a check and disable startup with shell in that
> case. This disabling is done temporary before forking
> inferior and restored after the fork.
> 
> gdb/ChangeLog:
> 
>         * darwin-nat.c (should_disable_startup_with_shell):
>         New function.
>         (darwin_nat_target::create_inferior): Add call.
> 
> Change-Id: Ie4d9090f65fdf2e83ecf7a0f9d0647fb1c27cdcc
> ---
>  gdb/darwin-nat.c | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/gdb/darwin-nat.c b/gdb/darwin-nat.c
> index be80163d22e..d23706d79fd 100644
> --- a/gdb/darwin-nat.c
> +++ b/gdb/darwin-nat.c
> @@ -1854,15 +1854,47 @@ darwin_execvp (const char *file, char * const
> argv[], char * const env[])
>    posix_spawnp (NULL, argv[0], NULL, &attr, argv, env);
>  }
> 
> +/* Read kernel version, and return false on Sierra or later.  */

I think this is the other way around (return trun on Sierra or later).

> +
> +static int
> +should_disable_startup_with_shell ()
> +{
> +  char str[16];
> +  size_t sz = sizeof (str);
> +  int ret;
> +
> +  ret = sysctlbyname ("kern.osrelease", str, &sz, NULL, 0);
> +  if (ret == 0 && sz < sizeof (str))
> +    {
> +      unsigned long ver = strtoul (str, NULL, 10);
> +      if (ver >= 16)
> +        return TRUE;
> +    }
> +  return FALSE;
> +}
> +
>  void
>  darwin_nat_target::create_inferior (const char *exec_file,
>  				    const std::string &allargs,
>  				    char **env, int from_tty)
>  {
> +  gdb::optional<scoped_restore_tmpl<int>> restore_startup_with_shell;
> +  int startup_shell_disabled = 0;
> +
> +  if (startup_with_shell && should_disable_startup_with_shell ())
> +    {
> +      warning (_("startup-with-shell not supported on this macOS
> version, disabling it."));
> +      restore_startup_with_shell.emplace (&startup_with_shell, 0);
> +      startup_shell_disabled = 1;
> +    }
> +
>    /* Do the hard work.  */
>    fork_inferior (exec_file, allargs, env, darwin_ptrace_me,
>  		 darwin_ptrace_him, darwin_pre_ptrace, NULL,
>  		 darwin_execvp);
> +
> +  if (startup_shell_disabled)
> +    restore_startup_with_shell.emplace (&startup_with_shell, 1);

You shouldn't need this last bit, nor the startup_shell_disabled 
variable.  When it gets destroyed, the restore_startup_with_shell object 
takes care of restoring the value of the startup_with_shell variable to 
the value it had when it was constructed (the first emplace call).

In other words, this call:

   restore_startup_with_shell.emplace (&startup_with_shell, 0);

means "save the current value of startup_with_shell, then put 0 in it".

When the destructor of restore_startup_with_shell is called, it restores 
the saved value.

With that fixed, it would LGTM, although I did not try it because I 
don't have access to a Mac at the moment.

Simon