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1d7fe7f01b
cmd_list_element can contain a pointer to data that can be set and / or
shown. This is achieved with the void* VAR member which points to the
data that can be accessed, while the VAR_TYPE member (of type enum
var_types) indicates how to interpret the data pointed to.
With this pattern, the user of the cmd_list_element needs to know what
is the storage type associated with a given VAR_TYPES in order to do
the proper casting. No automatic safeguard is available to prevent
miss-use of the pointer. Client code typically looks something like:
switch (c->var_type)
{
case var_zuinteger:
unsigned int v = *(unsigned int*) c->var;
...
break;
case var_boolean:
bool v = *(bool *) c->var;
...
break;
...
}
This patch proposes to add an abstraction around the var_types and void*
pointer pair. The abstraction is meant to prevent the user from having
to handle the cast and verify that the data is read or written as a type
that is coherent with the setting's var_type. This is achieved by
introducing the struct setting which exposes a set of templated get /
set member functions. The template parameter is the type of the
variable that holds the referred variable.
Using those accessors allows runtime checks to be inserted in order to
ensure that the data pointed to has the expected type. For example,
instantiating the member functions with bool will yield something
similar to:
const bool &get<bool> () const
{
gdb_assert (m_var_type == var_boolean);
gdb_assert (m_var != nullptr);
return *static_cast<bool *> (m_var);
}
void set<bool> (const bool &var)
{
gdb_assert (m_var_type == var_boolean);
gdb_assert (m_var != nullptr);
*static_cast<bool *> (m_var) = var;
}
Using the new abstraction, our initial example becomes:
switch (c->var_type)
{
case var_zuinteger:
unsigned int v = c->var->get<unsigned int> ();
...
break;
case var_boolean:
bool v = c->var->get<bool> ();
...
break;
...
}
While the call site is still similar, the introduction of runtime checks
help ensure correct usage of the data.
In order to avoid turning the bulk of add_setshow_cmd_full into a
templated function, and following a suggestion from Pedro Alves, a
setting can be constructed from a pre validated type erased reference to
a variable. This is what setting::erased_args is used for.
Introducing an opaque abstraction to describe a setting will also make
it possible to use callbacks to retrieve or set the value of the setting
on the fly instead of pointing to a static chunk of memory. This will
be done added in a later commit.
Given that a cmd_list_element may or may not reference a setting, the
VAR and VAR_TYPES members of the struct are replaced with a
gdb::optional<setting> named VAR.
Few internal function signatures have been modified to take into account
this new abstraction:
-The functions value_from_setting, str_value_from_setting and
get_setshow_command_value_string used to have a 'cmd_list_element *'
parameter but only used it for the VAR and VAR_TYPE member. They now
take a 'const setting &' parameter instead.
- Similarly, the 'void *' and a 'enum var_types' parameters of
pascm_param_value and gdbpy_parameter_value have been replaced with a
'const setting &' parameter.
No user visible change is expected after this patch.
Tested on GNU/Linux x86_64, with no regression noticed.
Co-authored-by: Simon Marchi <simon.marchi@polymtl.ca>
Change-Id: Ie1d08c3ceb8b30b3d7bf1efe036eb8acffcd2f34
66 lines
2.7 KiB
C++
66 lines
2.7 KiB
C++
/* Header file for GDB CLI set and show commands implementation.
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Copyright (C) 2000-2021 Free Software Foundation, Inc.
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>. */
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#ifndef CLI_CLI_SETSHOW_H
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#define CLI_CLI_SETSHOW_H
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#include <string>
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struct cmd_list_element;
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/* Parse ARG, an option to a boolean variable.
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Returns 1 for true, 0 for false, and -1 if invalid. */
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extern int parse_cli_boolean_value (const char *arg);
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/* Same as above, but work with a pointer to pointer. ARG is advanced
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past a successfully parsed value. */
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extern int parse_cli_boolean_value (const char **arg);
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/* Parse ARG, an option to a var_uinteger or var_zuinteger variable.
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Either returns the parsed value on success or throws an error. If
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EXPRESSION is true, *ARG is parsed as an expression; otherwise, it
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is parsed with get_ulongest. It's not possible to parse the
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integer as an expression when there may be valid input after the
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integer, such as when parsing command options. E.g., "print
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-elements NUMBER -obj --". In such case, parsing as an expression
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would parse "-obj --" as part of the expression as well. */
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extern unsigned int parse_cli_var_uinteger (var_types var_type,
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const char **arg,
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bool expression);
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/* Like parse_cli_var_uinteger, for var_zuinteger_unlimited. */
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extern int parse_cli_var_zuinteger_unlimited (const char **arg,
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bool expression);
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/* Parse ARG, an option to a var_enum variable. ENUM is a
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null-terminated array of possible values. Either returns the parsed
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value on success or throws an error. ARG is advanced past the
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parsed value. */
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const char *parse_cli_var_enum (const char **args,
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const char *const *enums);
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extern void do_set_command (const char *arg, int from_tty,
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struct cmd_list_element *c);
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extern void do_show_command (const char *arg, int from_tty,
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struct cmd_list_element *c);
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/* Get a string version of VAR's value. */
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extern std::string get_setshow_command_value_string (const setting &var);
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extern void cmd_show_list (struct cmd_list_element *list, int from_tty);
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#endif /* CLI_CLI_SETSHOW_H */
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