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

[Xavier Roirand <roirand@adacore.com>]

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.  */
+
+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);
 }
 \f
 
-- 
2.15.2 (Apple Git-101.1)