This patch makes sure gdb compiled inside chroot works outside where python
environment is different.

It ported two changes sitting in android code base:
https://android-review.googlesource.com/c/toolchain/gdb/+/202979
https://android-review.googlesource.com/c/toolchain/gdb/+/515189

BUG: crbug.com/1051736

diff --git a/gdb/defs.h b/gdb/defs.h
index a44e18690..392126c36 100644
--- a/gdb/defs.h
+++ b/gdb/defs.h
@@ -669,4 +669,8 @@ DEF_ENUM_FLAGS_TYPE (enum user_selected_what_flag, user_selected_what);
 
 #include "utils.h"
 
+#ifdef HAVE_PYTHON
+extern int python_available (void);
+#endif
+
 #endif /* #ifndef DEFS_H */
diff --git a/gdb/python/py-auto-load.c b/gdb/python/py-auto-load.c
index c7b9afdb1..db53acae9 100644
--- a/gdb/python/py-auto-load.c
+++ b/gdb/python/py-auto-load.c
@@ -46,6 +46,8 @@ show_auto_load_python_scripts (struct ui_file *file, int from_tty,
 int
 gdbpy_auto_load_enabled (const struct extension_language_defn *extlang)
 {
+  if (!python_available ())
+    return 0;
   return auto_load_python_scripts;
 }
 
diff --git a/gdb/python/py-prettyprint.c b/gdb/python/py-prettyprint.c
index 8effa81d5..62b3e08a4 100644
--- a/gdb/python/py-prettyprint.c
+++ b/gdb/python/py-prettyprint.c
@@ -664,7 +664,7 @@ gdbpy_apply_val_pretty_printer (const struct extension_language_defn *extlang,
   if (!value_bytes_available (val, embedded_offset, TYPE_LENGTH (type)))
     return EXT_LANG_RC_NOP;
 
-  if (!gdb_python_initialized)
+  if (!python_available () || !gdb_python_initialized)
     return EXT_LANG_RC_NOP;
 
   gdbpy_enter enter_py (gdbarch, language);
diff --git a/gdb/python/python.c b/gdb/python/python.c
index c23db2c12..6bf492dd5 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -33,6 +33,13 @@
 #include "python.h"
 #include "extension-priv.h"
 #include "cli/cli-utils.h"
+
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+
+#include <sys/types.h>
+#include <sys/wait.h>
 #include <ctype.h>
 #include "location.h"
 #include "ser-event.h"
@@ -1635,6 +1642,9 @@ do_start_initialization ()
 #endif
 #endif
 
+  if (!python_available ())
+    return true;
+
   Py_Initialize ();
   PyEval_InitThreads ();
 
@@ -1751,6 +1761,44 @@ do_start_initialization ()
 /* See python.h.  */
 cmd_list_element *python_cmd_element = nullptr;
 
+#ifdef HAVE_PYTHON
+/* Check whether python is available at runtime. */
+
+int
+python_available(void)
+{
+#ifndef HAVE_WORKING_FORK
+  return 1;
+#endif
+
+  static int python_status = -1;
+  int child_status = 0;
+
+  if (python_status != -1)
+    return python_status;
+
+  pid_t pid = fork ();
+
+  if (pid < 0)
+    perror_with_name (("fork"));
+
+  if (pid == 0)
+    {
+      freopen ("/dev/null", "w", stderr);
+      Py_Initialize ();
+      _exit(0);
+    }
+
+  wait (&child_status);
+  if (WIFEXITED (child_status) && WEXITSTATUS (child_status) == 0)
+    python_status = 1;
+  else
+    python_status = 0;
+
+  return python_status;
+}
+#endif
+
 void
 _initialize_python (void)
 {
@@ -1825,7 +1873,7 @@ message == an error message without a stack will be printed."),
 			&user_show_python_list);
 
 #ifdef HAVE_PYTHON
-  if (!do_start_initialization () && PyErr_Occurred ())
+  if (!do_start_initialization () && python_available () && PyErr_Occurred ())
     gdbpy_print_stack ();
 #endif /* HAVE_PYTHON */
 }
@@ -1904,6 +1952,9 @@ do_finish_initialization (const struct extension_language_defn *extlang)
 static void
 gdbpy_finish_initialization (const struct extension_language_defn *extlang)
 {
+  if (!python_available())
+    return;
+
   gdbpy_enter enter_py (get_current_arch (), current_language);
 
   if (!do_finish_initialization (extlang))
diff --git a/gdb/varobj.c b/gdb/varobj.c
index b03307068..13a6fa3bf 100644
--- a/gdb/varobj.c
+++ b/gdb/varobj.c
@@ -542,7 +542,7 @@ varobj_get_display_hint (const struct varobj *var)
   gdb::unique_xmalloc_ptr<char> result;
 
 #if HAVE_PYTHON
-  if (!gdb_python_initialized)
+  if (!python_available () || !gdb_python_initialized)
     return NULL;
 
   gdbpy_enter_varobj enter_py (var);
@@ -676,7 +676,7 @@ dynamic_varobj_has_child_method (const struct varobj *var)
 {
   PyObject *printer = var->dynamic->pretty_printer;
 
-  if (!gdb_python_initialized)
+  if (!python_available () || !gdb_python_initialized)
     return false;
 
   gdbpy_enter_varobj enter_py (var);
@@ -1181,7 +1181,7 @@ install_new_value_visualizer (struct varobj *var)
 #if HAVE_PYTHON
   /* If the constructor is None, then we want the raw value.  If VAR
      does not have a value, just skip this.  */
-  if (!gdb_python_initialized)
+  if (!python_available () || !gdb_python_initialized)
     return;
 
   if (var->dynamic->constructor != Py_None && var->value != NULL)
@@ -1450,7 +1450,7 @@ varobj_set_visualizer (struct varobj *var, const char *visualizer)
 #if HAVE_PYTHON
   PyObject *mainmod;
 
-  if (!gdb_python_initialized)
+  if (!python_available () || !gdb_python_initialized)
     return;
 
   gdbpy_enter_varobj enter_py (var);
@@ -2298,7 +2298,7 @@ varobj_value_get_print_value (struct value *value,
   std::string thevalue;
 
 #if HAVE_PYTHON
-  if (gdb_python_initialized)
+  if (python_available () && gdb_python_initialized)
     {
       PyObject *value_formatter =  var->dynamic->pretty_printer;