Make exceptions use std::string and be self-managing

This changes the exception's "message" member to be a shared_ptr
wrapping a std::string.  This allows removing the stack of exception
messages, because now exceptions will self-destruct when needed.  This
also adds a noexcept copy constructor and operator= to gdb_exception,
plus a "what" method.

gdb/ChangeLog
2019-04-08  Tom Tromey  <tom@tromey.com>

	* xml-support.c (gdb_xml_parser::parse): Update.
	* x86-linux-nat.c (x86_linux_nat_target::enable_btrace): Update.
	* value.c (show_convenience): Update.
	* unittests/cli-utils-selftests.c (test_number_or_range_parser)
	(test_parse_flags_qcs): Update.
	* thread.c (thr_try_catch_cmd): Update.
	* target.c (target_translate_tls_address): Update.
	* stack.c (print_frame_arg, read_frame_local, read_frame_arg)
	(info_frame_command_core, frame_apply_command_count): Update.
	* rust-exp.y (rust_lex_exception_test): Update.
	* riscv-tdep.c (riscv_print_one_register_info): Update.
	* remote.c (remote_target::enable_btrace): Update.
	* record-btrace.c (record_btrace_enable_warn): Update.
	* python/py-utils.c (gdbpy_convert_exception): Update.
	* printcmd.c (do_one_display, print_variable_and_value): Update.
	* mi/mi-main.c (mi_print_exception): Update.
	* mi/mi-interp.c (mi_cmd_interpreter_exec): Use SCOPE_EXIT.
	* mi/mi-cmd-stack.c (list_arg_or_local): Update.
	* linux-nat.c (linux_nat_target::attach): Update.
	* linux-fork.c (class scoped_switch_fork_info): Update.
	* infrun.c (displaced_step_prepare): Update.
	* infcall.c (call_function_by_hand_dummy): Update.
	* guile/scm-exception.c (gdbscm_scm_from_gdb_exception): Update.
	* gnu-v3-abi.c (print_one_vtable): Update.
	* frame.c (get_prev_frame_always): Update.
	* f-valprint.c (info_common_command_for_block): Update.
	* exec.c (try_open_exec_file): Update.
	* exceptions.c (print_exception, exception_print)
	(exception_fprintf, exception_print_same): Update.
	* dwarf2-frame.c (dwarf2_build_frame_info): Update.
	* dwarf-index-cache.c (index_cache::store)
	(index_cache::lookup_gdb_index): Update.
	* darwin-nat.c (maybe_cache_shell): Update.
	* cp-valprint.c (cp_print_value_fields): Update.
	* compile/compile-cplus-symbols.c (gcc_cplus_convert_symbol)
	(gcc_cplus_symbol_address): Update.
	* compile/compile-c-symbols.c (gcc_convert_symbol)
	(gcc_symbol_address, generate_c_for_for_one_variable): Update.
	* common/selftest.c: Update.
	* common/common-exceptions.h (struct gdb_exception) <message>: Now
	a std::string.
	(exception_try_scope_entry, exception_try_scope_exit): Don't
	declare.
	(struct exception_try_scope): Remove.
	(TRY): Don't use exception_try_scope.
	(struct gdb_exception): Add constructor, operator=.
	<what>: New method.
	(struct gdb_exception_RETURN_MASK_ALL)
	(struct gdb_exception_RETURN_MASK_ERROR)
	(struct gdb_exception_RETURN_MASK_QUIT): Add constructor.
	(struct gdb_quit_bad_alloc): Update.
	* common/common-exceptions.c (exception_none): Change
	initializer.
	(struct catcher) <state, exception>: Initialize inline.
	<prev>: Remove member.
	(current_catcher): Remove.
	(catchers): New global.
	(exceptions_state_mc_init): Simplify.
	(catcher_pop): Remove.
	(exceptions_state_mc, exceptions_state_mc_catch): Update.
	(try_scope_depth, exception_try_scope_entry)
	(exception_try_scope_exit): Remove.
	(throw_exception_sjlj): Update.
	(exception_messages, exception_messages_size): Remove.
	(throw_it): Simplify.
	(gdb_exception_sliced_copy): Remove.
	(throw_exception_cxx): Update.
	* cli/cli-script.c (script_from_file): Update.
	* breakpoint.c (insert_bp_location, update_breakpoint_locations):
	Update.
	* ada-valprint.c (ada_val_print): Update.
	* ada-lang.c (ada_to_fixed_type_1, ada_exception_name_addr)
	(create_excep_cond_exprs): Update.

gdb/gdbserver/ChangeLog
2019-04-08  Tom Tromey  <tom@tromey.com>

	* server.c (handle_btrace_general_set, handle_qxfer_btrace)
	(handle_qxfer_btrace_conf, detach_or_kill_for_exit_cleanup)
	(captured_main, main): Update.
	* gdbreplay.c (main): Update.

1 files changed, 55 insertions, 26 deletions

diff --git a/gdb/common/common-exceptions.h b/gdb/common/common-exceptions.h
index 6cc09ea..54e7404 100644
--- a/gdb/common/common-exceptions.h
+++ b/gdb/common/common-exceptions.h
@@ -22,6 +22,7 @@
 
 #include <setjmp.h>
 #include <new>
+#include <memory>
 
 /* Reasons for calling throw_exceptions().  NOTE: all reason values
    must be different from zero.  enum value 0 is reserved for internal
@@ -110,9 +111,47 @@ enum errors {
 
 struct gdb_exception
 {
+  gdb_exception ()
+    : reason ((enum return_reason) 0),
+      error (GDB_NO_ERROR)
+  {
+  }
+
+  gdb_exception (enum return_reason r, enum errors e)
+    : reason (r),
+      error (e)
+  {
+  }
+
+  /* The copy constructor exists so that we can mark it "noexcept",
+     which is a good practice for any sort of exception object.  */
+  gdb_exception (const gdb_exception &other) noexcept
+    : reason (other.reason),
+      error (other.error),
+      message (other.message)
+  {
+  }
+
+  /* The assignment operator exists so that we can mark it "noexcept",
+     which is a good practice for any sort of exception object.  */
+  gdb_exception &operator= (const gdb_exception &other) noexcept
+  {
+    reason = other.reason;
+    error = other.error;
+    message = other.message;
+    return *this;
+  }
+
+  /* Return the contents of the exception message, as a C string.  The
+     string remains owned by the exception object.  */
+  const char *what () const noexcept
+  {
+    return message->c_str ();
+  }
+
   enum return_reason reason;
   enum errors error;
-  const char *message;
+  std::shared_ptr<std::string> message;
 };
 
 /* Functions to drive the sjlj-based exceptions state machine.  Though
@@ -127,8 +166,6 @@ extern int exceptions_state_mc_catch (struct gdb_exception *, int);
 
 /* For the C++ try/catch-based TRY/CATCH mechanism.  */
 
-extern void *exception_try_scope_entry (void);
-extern void exception_try_scope_exit (void *saved_state);
 extern void exception_rethrow (void) ATTRIBUTE_NORETURN;
 
 /* Macro to wrap up standard try/catch behavior.
@@ -178,23 +215,6 @@ extern void exception_rethrow (void) ATTRIBUTE_NORETURN;
 #define END_CATCH_SJLJ				\
   }
 
-/* Prevent error/quit during TRY from calling cleanups established
-   prior to here.  This pops out the scope in either case of normal
-   exit or exception exit.  */
-struct exception_try_scope
-{
-  exception_try_scope ()
-  {
-    saved_state = exception_try_scope_entry ();
-  }
-  ~exception_try_scope ()
-  {
-    exception_try_scope_exit (saved_state);
-  }
-
-  void *saved_state;
-};
-
 /* We still need to wrap TRY/CATCH in C++ so that cleanups and C++
    exceptions can coexist.
 
@@ -214,7 +234,6 @@ struct exception_try_scope
   {									\
     try									\
       {									\
-	exception_try_scope exception_try_scope_instance;		\
 	do								\
 	  {
 
@@ -236,14 +255,26 @@ struct exception_try_scope
 
 struct gdb_exception_RETURN_MASK_ALL : public gdb_exception
 {
+  explicit gdb_exception_RETURN_MASK_ALL (const gdb_exception &ex) noexcept
+    : gdb_exception (ex)
+  {
+  }
 };
 
 struct gdb_exception_RETURN_MASK_ERROR : public gdb_exception_RETURN_MASK_ALL
 {
+  explicit gdb_exception_RETURN_MASK_ERROR (const gdb_exception &ex) noexcept
+    : gdb_exception_RETURN_MASK_ALL (ex)
+  {
+  }
 };
 
 struct gdb_exception_RETURN_MASK_QUIT : public gdb_exception_RETURN_MASK_ALL
 {
+  explicit gdb_exception_RETURN_MASK_QUIT (const gdb_exception &ex) noexcept
+    : gdb_exception_RETURN_MASK_ALL (ex)
+  {
+  }
 };
 
 /* An exception type that inherits from both std::bad_alloc and a gdb
@@ -256,12 +287,10 @@ struct gdb_quit_bad_alloc
   : public gdb_exception_RETURN_MASK_QUIT,
     public std::bad_alloc
 {
-  explicit gdb_quit_bad_alloc (gdb_exception ex)
-    : std::bad_alloc ()
+  explicit gdb_quit_bad_alloc (const gdb_exception &ex) noexcept
+    : gdb_exception_RETURN_MASK_QUIT (ex),
+      std::bad_alloc ()
   {
-    gdb_exception *self = this;
-
-    *self = ex;
   }
 };