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gdb: Setting setter return a bool to tell if the value changed

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GDB can notify observers when a parameter is changed.

To do that, do_set_command (in gdb/cli/cli-setshow.c) compares the new
value against the old one before updating it, and based on that notifies
observers.  This looks like something like:

    int valuechanged = 0;
    switch (cmd->var.type ())
    {
    case var_integer:
      {
        LONGEST new_val = parse_and_eval_long (arg)
        if (new_val != cmd->var.get<int> ())
        {
          cmd->var.get<int> (new_val);
          value_changes = 1;
        }
      }
    case var_uinteger:
    case var_zuinteger:
      {
        unsigned int val
          = parse_cli_var_uinteger (c->var->type (), &arg, true);
        if (c->var->get<unsigned int> () != val)
          {
            c->var->set<unsigned int> (val);
            option_changed = true;
          }
      }
    case...
      /* And so on for all possible var_types.  */
    }

This comparison is done for each possible var_type, which leads to
unnecessary logic duplication.

In this patch I propose to move all those checks in one place within the
setting setter method.  This limits the code duplication and simplifies
the do_set_command implementation.

This patch also changes slightly the way a value change is detected.
Instead of comparing the user provided value against the current value
of the setting, we compare the value of the setting before and after the
set operation.  This is meant to handle edge cases where trying to set
an unrecognized value would be equivalent to a noop (the actual value
remains unchanged).  Doing this requires that the original value needs
to be copied before the update, which can be non trivial for
std::string.

There should be no user visible change introduced by this commit.

Tested on x86_64 GNU/Linux.

[1] https://review.lttng.org/c/binutils-gdb/+/5831/41

Change-Id: If064b9cede3eb56275aacd2b286f74eceb1aed11
This commit is contained in:
Lancelot SIX 2021-09-14 23:37:25 +01:00
parent 702991711a
commit 1a98bb552d
2 changed files with 21 additions and 72 deletions
Download patch file Download diff file Expand all files Collapse all files

83
gdb/cli/cli-setshow.c
View file

@ -360,26 +360,12 @@ do_set_command (const char *arg, int from_tty, struct cmd_list_element *c)
*q++ = '\0';
newobj = (char *) xrealloc (newobj, q - newobj);
const std::string &cur_val = c->var->get<std::string> ();
if (strcmp (cur_val.c_str(), newobj) != 0)
{
c->var->set<std::string> (std::string (newobj));
option_changed = true;
}
option_changed = c->var->set<std::string> (std::string (newobj));
xfree (newobj);
}
break;
case var_string_noescape:
{
const std::string &cur_val = c->var->get<std::string> ();
if (strcmp (cur_val.c_str (), arg) != 0)
{
c->var->set<std::string> (std::string (arg));
option_changed = true;
}
}
option_changed = c->var->set<std::string> (std::string (arg));
break;
case var_filename:
if (*arg == '\0')
@ -405,13 +391,8 @@ do_set_command (const char *arg, int from_tty, struct cmd_list_element *c)
else
val = xstrdup ("");
const std::string &cur_val = c->var->get<std::string> ();
if (strcmp (cur_val.c_str (), val) != 0)
{
c->var->set<std::string> (std::string (val));
option_changed = true;
}
option_changed
= c->var->set<std::string> (std::string (val));
xfree (val);
}
break;
@ -421,39 +402,18 @@ do_set_command (const char *arg, int from_tty, struct cmd_list_element *c)
if (val < 0)
error (_("\"on\" or \"off\" expected."));
if (val != c->var->get<bool> ())
{
c->var->set<bool> (val);
option_changed = true;
}
option_changed = c->var->set<bool> (val);
}
break;
case var_auto_boolean:
{
enum auto_boolean val = parse_auto_binary_operation (arg);
if (c->var->get<enum auto_boolean> () != val)
{
c->var->set<enum auto_boolean> (val);
option_changed = true;
}
}
option_changed = c->var->set<enum auto_boolean> (parse_auto_binary_operation (arg));
break;
case var_uinteger:
case var_zuinteger:
{
unsigned int val
= parse_cli_var_uinteger (c->var->type (), &arg, true);
if (c->var->get<unsigned int> () != val)
{
c->var->set<unsigned int> (val);
option_changed = true;
}
}
option_changed
= c->var->set<unsigned int> (parse_cli_var_uinteger (c->var->type (),
&arg, true));
break;
case var_integer:
case var_zinteger:
@ -483,12 +443,7 @@ do_set_command (const char *arg, int from_tty, struct cmd_list_element *c)
|| (c->var->type () == var_zinteger && val > INT_MAX))
error (_("integer %s out of range"), plongest (val));
if (c->var->get<int> () != val)
{
c->var->set<int> (val);
option_changed = true;
}
option_changed = c->var->set<int> (val);
}
break;
case var_enum:
@ -501,24 +456,12 @@ do_set_command (const char *arg, int from_tty, struct cmd_list_element *c)
if (*after != '\0')
error (_("Junk after item \"%.*s\": %s"), len, arg, after);
if (c->var->get<const char *> () != match)
{
c->var->set<const char *> (match);
option_changed = true;
}
option_changed = c->var->set<const char *> (match);
}
break;
case var_zuinteger_unlimited:
{
int val = parse_cli_var_zuinteger_unlimited (&arg, true);
if (c->var->get<int> () != val)
{
c->var->set<int> (val);
option_changed = true;
}
}
option_changed = c->var->set<int>
(parse_cli_var_zuinteger_unlimited (&arg, true));
break;
default:
error (_("gdb internal error: bad var_type in do_setshow_command"));

10
gdb/command.h
View file

@ -300,7 +300,9 @@ struct setting
return *static_cast<const T *> (m_var);
}
/* Sets the value of the setting to V.
/* Sets the value of the setting to V. Returns true if the setting was
effectively changed, false if the update failed and the setting is left
unchanged.
If we have a user-provided setter, use it to set the setting. Otherwise
copy the value V to the internally referenced buffer.
@ -310,12 +312,14 @@ struct setting
The var_type of the setting must match T. */
template<typename T>
void set (const T &v)
bool set (const T &v)
{
/* Check that the current instance is of one of the supported types for
this instantiation. */
gdb_assert (var_type_uses<T> (m_var_type));
const T old_value = this->get<T> ();
if (m_var == nullptr)
{
gdb_assert (m_setter != nullptr);
@ -324,6 +328,8 @@ struct setting
}
else
*static_cast<T *> (m_var) = v;
return old_value != this->get<T> ();
}
private: