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

[Simon Marchi]

On 2018-08-22 06:11, 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.

Ah, that's a really good idea to do it automatically, instead of asking 
the user to do it.

> gdb/ChangeLog:
>     * darwin-nat.c (disable_startup_with_shell): New function.
>     (_initialize_darwin_inferior): Add call.
> 
> Change-Id: Ia3cbeaa89b2b44a173b93ee22cce0d3884a16924
> ---
>  gdb/darwin-nat.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/gdb/darwin-nat.c b/gdb/darwin-nat.c
> index be80163..96f70cf 100644
> --- a/gdb/darwin-nat.c
> +++ b/gdb/darwin-nat.c
> @@ -2362,6 +2362,26 @@ darwin_nat_target::supports_multi_process ()
>    return true;
>  }
> 
> +/* Read kernel version, and set startup-with-shell to false on Sierra 
> or
> +   later.  */
> +
> +void
> +disable_startup_with_shell ()

This function should be static.

> +{
> +  char str[16];
> +    size_t sz = sizeof (str);
> +    int ret;
> +    unsigned long ver;
> +
> +    ret = sysctlbyname ("kern.osrelease", str, &sz, NULL, 0);
> +    if (ret == 0 && sz < sizeof (str))
> +      {
> +       ver = strtoul (str, NULL, 10);
> +       if (ver >= 16)
> +         startup_with_shell = 0;
> +      }
> +}

The indentation is not quite right.  You can also declare variables when 
they are used/initialized.

> +
>  void
>  _initialize_darwin_nat ()
>  {
> @@ -2396,4 +2416,6 @@ When this mode is on, all low level exceptions
> are reported before being\n\
>  reported by the kernel."),
>  			   &set_enable_mach_exceptions, NULL,
>  			   &setlist, &showlist);
> +
> +  disable_startup_with_shell ();
>  }

I don't think we should do that in _initialize_darwin_nat.  Since 
startup-with-shell is supported with remote debugging, you could still 
use it when starting a Linux remote program from a macOS host.

Instead, we should probably only disable it at the moment we create a 
new inferior in the darwin_nat target, so in 
darwin_nat_target::create_inferior.  We also don't want to permanently 
change the setting, so we should restore the value.  Presumably, putting 
something like this in darwin_nat_target::create_inferior should work (I 
haven't tested it, and sorry for the potential formatting mess my email 
client will do):

   gdb::optional<scoped_restore_tmpl<int>> restore_startup_with_shell;
   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);
     }

Instead of setting/restoring startup_with_shell, it might be better if 
its value was passed as a parameter all the way down instead of having 
functions read the global variable, but that's a bigger job.

Simon