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* [PATCH] [gdb/mi] Don't treat references to compound values as "simple".
@ 2022-09-08  7:18 Gareth Rees
  2022-09-08 10:27 ` Andrew Burgess
  0 siblings, 1 reply; 49+ messages in thread
From: Gareth Rees @ 2022-09-08  7:18 UTC (permalink / raw)
  To: gdb-patches

SUMMARY

The '--simple-values' argument to '-stack-list-arguments' and similar
GDB/MI commands does not take reference types into account, so that
references to arbitrarily large structures are considered "simple" and
printed. This means that the '--simple-values' argument cannot be used
by IDEs when tracing the stack due to the time taken to print large
structures passed by reference.

DETAILS

Various GDB/MI commands ('-stack-list-arguments', '-stack-list-locals',
'-stack-list-variables' and so on) take a PRINT-VALUES argument which
may be '--no-values' (0), '--all-values' (1) or '--simple-values' (2).
In the '--simple-values' case, the command is supposed to print the
name, type, and value of variables with simple types, and print only the
name and type of variables with compound types.

The '--simple-values' argument ought to be suitable for IDEs that need
to update their user interface with the program's call stack every time
the program stops. However, it does not take C++ reference types into
account, and this makes the argument unsuitable for this purpose.

For example, consider the following C++ program:

    struct s {
        int v[10];
    };

    int
    sum(const struct s &s)
    {
        int total = 0;
        for (int i = 0; i < 10; ++i) total += s.v[i];
        return total;
    }

    int
    main(void)
    {
        struct s s = { { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 } };
        return sum(s);
    }

If we start GDB in MI mode and continue to 'sum', the behaviour of
'-stack-list-arguments' is as follows:

    (gdb)
    -stack-list-arguments --simple-values
    ^done,stack-args=[frame={level="0",args=[{name="s",type="const s &",value="@0x7fffffffe310: {v = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}}"}]},frame={level="1",args=[]}]

Note that the value of the argument 's' was printed, even though 's' is
a reference to a structure, which is not a simple value.

See https://github.com/microsoft/MIEngine/pull/673 for a case where this
behaviour caused Microsoft to avoid the use of '--simple-values' in
their MIEngine debug adapter, because it caused Visual Studio Code to
take too long to refresh the call stack in the user interface.

SOLUTIONS

There are two ways we could fix this problem, depending on whether we
consider the current behaviour to be a bug.

1. If the current behaviour is a bug, then we can update the behaviour
   of '--simple-values' so that it takes reference types into account:
   that is, a value is simple if it is neither an array, struct, or
   union, nor a reference to an array, struct or union.

   In this case we must add a feature to the '-list-features' command so
   that IDEs can detect that it is safe to use the '--simple-values'
   argument when refreshing the call stack.

2. If the current behaviour is not a bug, then we can add a new option
   for the PRINT-VALUES argument, for example, '--simplest-values' (3),
   that would be suitable for use by IDEs.

   In this case we must add a feature to the '-list-features' command so
   that IDEs can detect that the '--simplest-values' argument is
   available for use when refreshing the call stack.

PATCH

This patch implements solution (1) as I think the current behaviour of
not printing structures, but printing references to structures, is
surprising. However, if you prefer solution (2) I would be happy to
implement that instead.
---
 gdb/NEWS                                     | 12 ++++++
 gdb/doc/gdb.texinfo                          |  7 ++++
 gdb/mi/mi-cmd-stack.c                        |  6 +--
 gdb/mi/mi-cmd-var.c                          | 22 ++++++----
 gdb/mi/mi-cmds.h                             |  5 +++
 gdb/mi/mi-main.c                             |  7 +---
 gdb/python/py-framefilter.c                  |  6 +--
 gdb/testsuite/gdb.mi/print-simple-values.cc  | 44 ++++++++++++++++++++
 gdb/testsuite/gdb.mi/print-simple-values.exp | 40 ++++++++++++++++++
 9 files changed, 126 insertions(+), 23 deletions(-)
 create mode 100644 gdb/testsuite/gdb.mi/print-simple-values.cc
 create mode 100644 gdb/testsuite/gdb.mi/print-simple-values.exp

diff --git a/gdb/NEWS b/gdb/NEWS
index dee0ac2ecd8..855f42a9549 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -114,6 +114,18 @@ maintenance info line-table
   entry corresponds to an address where a breakpoint should be placed
   to be at the first instruction past a function's prologue.
 
+* MI changes
+
+  ** The '--simple-values' argument to the '-stack-list-arguments',
+     '-stack-list-locals', '-stack-list-variables', and
+     '-var-list-children' commands takes reference types into account:
+     that is, a value is now considered simple if it is neither an
+     array, structure, or union, nor a reference to an array, structure,
+     or union. (Previously all references were considered simple.)
+     Support for this feature can be verified by using the
+     '-list-features' command, which should contain
+     "simple-values-ref-types".
+
 * New targets
 
 GNU/Linux/LoongArch (gdbserver)	loongarch*-*-linux*
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 238a49b027d..5ccf6609709 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -37295,6 +37295,13 @@ option (@pxref{GDB/MI Program Execution}).
 @item data-disassemble-a-option
 Indicates that the @code{-data-disassemble} command supports the @option{-a}
 option (@pxref{GDB/MI Data Manipulation}).
+@item simple-values-ref-types
+Indicates that the @code{--simple-values} argument to the
+@code{-stack-list-arguments}, @code{-stack-list-locals},
+@code{-stack-list-variables}, and @code{-var-list-children} commands
+takes reference types into account: that is, a value is considered
+simple if it neither an array, structure, or union, nor a reference to
+an array, structure, or union.
 @end ftable
 
 @subheading The @code{-list-target-features} Command
diff --git a/gdb/mi/mi-cmd-stack.c b/gdb/mi/mi-cmd-stack.c
index 0fe204dbc66..f8f4ad266d0 100644
--- a/gdb/mi/mi-cmd-stack.c
+++ b/gdb/mi/mi-cmd-stack.c
@@ -571,7 +571,6 @@ list_args_or_locals (const frame_print_options &fp_opts,
   const struct block *block;
   struct symbol *sym;
   struct block_iterator iter;
-  struct type *type;
   const char *name_of_result;
   struct ui_out *uiout = current_uiout;
 
@@ -650,10 +649,7 @@ list_args_or_locals (const frame_print_options &fp_opts,
 	      switch (values)
 		{
 		case PRINT_SIMPLE_VALUES:
-		  type = check_typedef (sym2->type ());
-		  if (type->code () != TYPE_CODE_ARRAY
-		      && type->code () != TYPE_CODE_STRUCT
-		      && type->code () != TYPE_CODE_UNION)
+                  if (mi_simple_values_type_p (sym2->type ()))
 		    {
 		case PRINT_ALL_VALUES:
 		  if (sym->is_argument ())
diff --git a/gdb/mi/mi-cmd-var.c b/gdb/mi/mi-cmd-var.c
index 3db09cf7815..f9d332d13a4 100644
--- a/gdb/mi/mi-cmd-var.c
+++ b/gdb/mi/mi-cmd-var.c
@@ -335,15 +335,21 @@ mi_print_value_p (struct varobj *var, enum print_values print_values)
   if (type == NULL)
     return 1;
   else
-    {
-      type = check_typedef (type);
+    return mi_simple_values_type_p (type);
+}
 
-      /* For PRINT_SIMPLE_VALUES, only print the value if it has a type
-	 and that type is not a compound type.  */
-      return (type->code () != TYPE_CODE_ARRAY
-	      && type->code () != TYPE_CODE_STRUCT
-	      && type->code () != TYPE_CODE_UNION);
-    }
+int
+mi_simple_values_type_p (struct type *type)
+{
+  type = check_typedef (type);
+
+  if (type->code () == TYPE_CODE_REF || type->code () == TYPE_CODE_RVALUE_REF)
+    type = TYPE_TARGET_TYPE (type);
+
+  return (type
+          && type->code () != TYPE_CODE_ARRAY
+          && type->code () != TYPE_CODE_STRUCT
+          && type->code () != TYPE_CODE_UNION);
 }
 
 void
diff --git a/gdb/mi/mi-cmds.h b/gdb/mi/mi-cmds.h
index 9ffb11bf997..81a5578ca1c 100644
--- a/gdb/mi/mi-cmds.h
+++ b/gdb/mi/mi-cmds.h
@@ -226,4 +226,9 @@ using remove_mi_cmd_entries_ftype
   = gdb::function_view<bool (mi_command *)>;
 extern void remove_mi_cmd_entries (remove_mi_cmd_entries_ftype callback);
 
+/* Return 1 if type is suitable for printing with PRINT_SIMPLE_VALUES, that is,
+   if type is neither a compound type nor a reference to a compound type. */
+
+extern int mi_simple_values_type_p (struct type *type);
+
 #endif /* MI_MI_CMDS_H */
diff --git a/gdb/mi/mi-main.c b/gdb/mi/mi-main.c
index b758f398e2a..dd1962fd0e2 100644
--- a/gdb/mi/mi-main.c
+++ b/gdb/mi/mi-main.c
@@ -1663,6 +1663,7 @@ mi_cmd_list_features (const char *command, char **argv, int argc)
       uiout->field_string (NULL, "undefined-command-error-code");
       uiout->field_string (NULL, "exec-run-start-option");
       uiout->field_string (NULL, "data-disassemble-a-option");
+      uiout->field_string (NULL, "simple-values-ref-types");
 
       if (ext_lang_initialized_p (get_ext_lang_defn (EXT_LANG_PYTHON)))
 	uiout->field_string (NULL, "python");
@@ -2462,7 +2463,6 @@ static void
 print_variable_or_computed (const char *expression, enum print_values values)
 {
   struct value *val;
-  struct type *type;
   struct ui_out *uiout = current_uiout;
 
   string_file stb;
@@ -2482,12 +2482,9 @@ print_variable_or_computed (const char *expression, enum print_values values)
   switch (values)
     {
     case PRINT_SIMPLE_VALUES:
-      type = check_typedef (value_type (val));
       type_print (value_type (val), "", &stb, -1);
       uiout->field_stream ("type", stb);
-      if (type->code () != TYPE_CODE_ARRAY
-	  && type->code () != TYPE_CODE_STRUCT
-	  && type->code () != TYPE_CODE_UNION)
+      if (mi_simple_values_type_p (value_type (val)))
 	{
 	  struct value_print_options opts;
 
diff --git a/gdb/python/py-framefilter.c b/gdb/python/py-framefilter.c
index 366f3745b9d..227a9ecb4f1 100644
--- a/gdb/python/py-framefilter.c
+++ b/gdb/python/py-framefilter.c
@@ -235,14 +235,10 @@ py_print_value (struct ui_out *out, struct value *val,
   if (args_type == MI_PRINT_SIMPLE_VALUES
       || args_type == MI_PRINT_ALL_VALUES)
     {
-      struct type *type = check_typedef (value_type (val));
-
       if (args_type == MI_PRINT_ALL_VALUES)
 	should_print = 1;
       else if (args_type == MI_PRINT_SIMPLE_VALUES
-	       && type->code () != TYPE_CODE_ARRAY
-	       && type->code () != TYPE_CODE_STRUCT
-	       && type->code () != TYPE_CODE_UNION)
+	       && mi_simple_values_type_p (value_type (val)))
 	should_print = 1;
     }
   else if (args_type != NO_VALUES)
diff --git a/gdb/testsuite/gdb.mi/print-simple-values.cc b/gdb/testsuite/gdb.mi/print-simple-values.cc
new file mode 100644
index 00000000000..15567c740a0
--- /dev/null
+++ b/gdb/testsuite/gdb.mi/print-simple-values.cc
@@ -0,0 +1,44 @@
+/* This test case is part of GDB, the GNU debugger.
+
+   Copyright 2022 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* PRINT_SIMPLE_VALUES test program.
+
+   Test that PRINT_SIMPLE_VALUES handles C++ reference types correctly.
+
+   In the function f(), arguments a, b, and c are either ints or references to
+   int, and their values should be printed by PRINT_SIMPLE_VALUES, but arguments
+   s, t, and u are structures or references to structures, and their values
+   should not be printed by PRINT_SIMPLE_VALUES. */
+
+struct s
+{
+    int v;
+};
+
+int
+f(int a, int &b, int &&c, struct s s, struct s &t, struct s &&u)
+{
+    return a + b + c + s.v + t.v + u.v;
+}
+
+int
+main(void)
+{
+    int a = 1, b = 2;
+    struct s s = { 4 }, t = { 5 };
+    return f(a, b, 3, s, t, (struct s){ 6 });
+}
diff --git a/gdb/testsuite/gdb.mi/print-simple-values.exp b/gdb/testsuite/gdb.mi/print-simple-values.exp
new file mode 100644
index 00000000000..c1b5a54ad3b
--- /dev/null
+++ b/gdb/testsuite/gdb.mi/print-simple-values.exp
@@ -0,0 +1,40 @@
+# Copyright 2022 Free Software Foundation, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+if { [skip_cplus_tests] } { continue }
+
+load_lib mi-support.exp
+standard_testfile .cc
+
+if { [gdb_compile "$srcdir/$subdir/$srcfile" $binfile executable {debug c++}] != "" } {
+    untested "failed to compile"
+    return -1
+}
+
+mi_clean_restart $binfile
+
+mi_runto_main
+
+mi_gdb_test "-break-insert f" "\\^done.*" "set breakpoint on f"
+
+mi_send_resuming_command "exec-continue" "exec-continue to breakpoint on f"
+
+mi_expect_stop "breakpoint-hit" "f" ".*" ".*" ".*" {.* disp="keep"} "run until breakpoint on f"
+
+mi_gdb_test "-stack-list-arguments 2" \
+    "\\^done,stack-args=\\\[frame=\{level=\"0\",args=\\\[\{name=\"a\",type=\"int\",value=\"1\"\},\{name=\"b\",type=\"int &\",value=\"@0x\[0-9a-f\]+: 2\"\},\{name=\"c\",type=\"int &&\",value=\"@0x\[0-9a-f\]+: 3\"\},\{name=\"s\",type=\"s\"\},\{name=\"t\",type=\"s &\"\},\{name=\"u\",type=\"s &&\"\}\\\]\},frame=\{level=\"1\",args=\\\[\\\]\}\\\]" \
+    "stack list arguments, simple types: names, types and values, compound types: names and types"
+
+mi_gdb_exit
-- 
2.26.0


^ permalink raw reply	[flat|nested] 49+ messages in thread
end of thread, other threads:[~2023-05-04 15:08 UTC | newest]

Thread overview: 49+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-09-08  7:18 [PATCH] [gdb/mi] Don't treat references to compound values as "simple" Gareth Rees
2022-09-08 10:27 ` Andrew Burgess
2022-09-08 11:02   ` [PATCH v2] " Gareth Rees
2022-09-08 13:30     ` Eli Zaretskii
2022-09-08 13:58       ` Gareth Rees
2022-09-08 14:07         ` Eli Zaretskii
2022-09-09  8:01       ` [PATCH v3] [PR mi/29554] New PRINT-VALUES option '--scalar-values' Gareth Rees
2022-09-15  9:06         ` [PING] " Gareth Rees
2022-09-25  8:15         ` Gareth Rees
2022-09-25  8:25           ` Eli Zaretskii
2022-09-25  9:00             ` Gareth Rees
2022-09-25 10:16               ` Eli Zaretskii
2022-09-26 12:48                 ` Gareth Rees
2022-09-25 10:16           ` Eli Zaretskii
2022-09-26 12:46         ` [PATCH v4] " Gareth Rees
2022-10-04  9:08           ` [PING] " Gareth Rees
2022-10-18 11:59             ` Gareth Rees
2022-10-12 16:38           ` Andrew Burgess
2022-10-20 17:47             ` [PATCH v5] " Gareth Rees
2022-10-20 18:00               ` Eli Zaretskii
2022-11-03 16:20               ` [PING] " Gareth Rees
2022-11-14  9:25                 ` Gareth Rees
2022-12-01 13:41                 ` Gareth Rees
2022-12-14  8:50                 ` Gareth Rees
2023-02-01 10:00                 ` Gareth Rees
2023-02-16 10:08                 ` Gareth Rees
2023-03-06  9:52                 ` Gareth Rees
2023-03-08 12:35               ` Andrew Burgess
2023-03-10 11:04                 ` Gareth Rees
2023-03-10 12:05                   ` Eli Zaretskii
2023-03-10 12:58                     ` Gareth Rees
2023-03-13 17:17                     ` Andrew Burgess
2023-03-16 12:28                       ` Gareth Rees
2023-03-11 11:58                   ` Gareth Rees
2023-04-11 13:15                     ` Pedro Alves
2023-03-11 11:49               ` [PATCH v6] [gdb/mi] Don't treat references to compound values as "simple" Gareth Rees
2023-03-21  9:50                 ` [PING] " Gareth Rees
2023-03-26  9:56                   ` Gareth Rees
2023-04-03  9:22                     ` Gareth Rees
2023-05-04 15:08                       ` Tom Tromey
2023-04-18  9:23                   ` Gareth Rees
2023-04-24  9:53                   ` Gareth Rees
2023-05-02  9:13                   ` Gareth Rees
2023-03-27 14:34                 ` Tom Tromey
2023-03-29  9:14                   ` Gareth Rees
2023-04-06 17:18                   ` Gareth Rees
2022-10-20 17:58             ` [PATCH v4] [PR mi/29554] New PRINT-VALUES option '--scalar-values' Gareth Rees
2022-09-09  8:04       ` [PATCH v2] [gdb/mi] Don't treat references to compound values as "simple" Gareth Rees
2022-09-08 11:09   ` [PATCH] " Gareth Rees

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