Re: [PATCH 14/18] -Wwrite-strings: Add a PyArg_ParseTupleAndKeywords "const char *" overload

Pedro Alves
2017-04-05T12:58:08Z

On 04/04/2017 07:37 PM, Sergio Durigan Junior wrote:
> On Tuesday, April 04 2017, Pedro Alves wrote:

>> However, to avoid having all callers add the 'const_cast<char **>'
>> themselves, this commit define a PyArg_ParseTupleAndKeywords overload
>> here with a corresponding 'keywords' parameter type that does the cast
>> in a single place.
>>
>> As in the PyGetSetDef patch, I'd be fine with naming this
>> gdb_PyArg_ParseTupleAndKeywords instead, if people would find having
>> our own overload confusing.
>
> As much as I like the overloading approach in general, I prefer to see
> our own overloads marked with the "gdb_", just to make things clearer.

OK, updated patch below. WDYT?

>
>> BTW, this API issue was discussed years ago in the python-dev list:
>>
>> https://mail.python.org/pipermail/python-dev/2006-February/060689.html
>>
>> ... and an overload for C++ was suggested in there somewhere.
>> Unfortunately, it was never added.
>
> Interesting. I wonder if there's an actual bug/issue opened on their
> bugzilla about this.
>
> Hm, after a quick search I didn't find anything. Maybe it's worth
> creating one.

I had found that thread via this bug: https://bugs.python.org/issue1772673

From 2ea02b3a4f5e7e0a1ecfb206d8a5f04b37876bd2 Mon Sep 17 00:00:00 2001
From: Pedro Alves <palves@redhat.com>
Date: Wed, 5 Apr 2017 13:45:55 +0100
Subject: [PATCH] -Wwrite-strings: Add a PyArg_ParseTupleAndKeywords "const
char *" overload

-Wwrite-strings flags code like:

static char *keywords[] = {"command", "from_tty", "to_string", NULL };

as needing "(char *)" casts, because string literals are "const char []".

We can get rid of the casts by changing the array type like this:

- static char *keywords[] = {"command", "from_tty", "to_string", NULL };
+ static const char *keywords[] = {"command", "from_tty", "to_string", NULL };

However, passing the such array to PyArg_ParseTupleAndKeywords no longer
works OOTB, because PyArg_ParseTupleAndKeywords expects a "char **":

PyArg_ParseTupleAndKeywords(PyObject *args, PyObject *kw,
const char *format,
char *keywords[], ...);

and "const char **" is not implicitly convertible to "char **". C++
is more tolerant that C here WRT aliasing, and a const_cast<char **>
is fine. However, to avoid having all callers do the cast themselves,
this commit defines a gdb_PyArg_ParseTupleAndKeywords function here
with a corresponding 'keywords' parameter type that does the cast in a
single place.

gdb/ChangeLog:
yyyy-mm-dd Pedro Alves <palves@redhat.com>

* python/python-internal.h (gdb_PyArg_ParseTupleAndKeywords): New
static inline function.
* python/py-arch.c (archpy_disassemble): Constify 'keywords'
array and use gdb_PyArg_ParseTupleAndKeywords.
* python/py-cmd.c (cmdpy_init): Likewise.
* python/py-finishbreakpoint.c (bpfinishpy_init): Likewise.
* python/py-inferior.c (infpy_read_memory, infpy_write_memory)
(infpy_search_memory): Likewise.
* python/py-objfile.c (objfpy_add_separate_debug_file)
(gdbpy_lookup_objfile): Likewise.
* python/py-symbol.c (gdbpy_lookup_symbol)
(gdbpy_lookup_global_symbol): Likewise.
* python/py-type.c (gdbpy_lookup_type): Likewise.
* python/py-value.c (valpy_lazy_string, valpy_string): Likewise.
* python/python.c (execute_gdb_command, gdbpy_write, gdbpy_flush):
Likewise.
---
gdb/python/py-arch.c | 7 ++++---
gdb/python/py-breakpoint.c | 10 +++++-----
gdb/python/py-cmd.c | 10 +++++-----
gdb/python/py-finishbreakpoint.c | 6 +++---
gdb/python/py-inferior.c | 21 ++++++++++-----------
gdb/python/py-objfile.c | 10 +++++-----
gdb/python/py-symbol.c | 13 +++++++------
gdb/python/py-type.c | 6 +++---
gdb/python/py-value.c | 12 ++++++------
gdb/python/python-internal.h | 28 ++++++++++++++++++++++++++++
gdb/python/python.c | 20 ++++++++++----------
11 files changed, 86 insertions(+), 57 deletions(-)

diff --git a/gdb/python/py-arch.c b/gdb/python/py-arch.c
index 71d2989..cfadb47 100644
--- a/gdb/python/py-arch.c
+++ b/gdb/python/py-arch.c
@@ -116,7 +116,7 @@ archpy_name (PyObject *self, PyObject *args)
static PyObject *
archpy_disassemble (PyObject *self, PyObject *args, PyObject *kw)
{
- static char *keywords[] = { "start_pc", "end_pc", "count", NULL };
+ static const char *keywords[] = { "start_pc", "end_pc", "count", NULL };
CORE_ADDR start, end = 0;
CORE_ADDR pc;
gdb_py_ulongest start_temp;
@@ -126,8 +126,9 @@ archpy_disassemble (PyObject *self, PyObject *args, PyObject *kw)

ARCHPY_REQUIRE_VALID (self, gdbarch);

- if (!PyArg_ParseTupleAndKeywords (args, kw, GDB_PY_LLU_ARG "|OO", keywords,
- &start_temp, &end_obj, &count_obj))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, GDB_PY_LLU_ARG "|OO",
+ keywords, &start_temp, &end_obj,
+ &count_obj))
return NULL;

start = start_temp;
diff --git a/gdb/python/py-breakpoint.c b/gdb/python/py-breakpoint.c
index 34f46fb..a08501e 100644
--- a/gdb/python/py-breakpoint.c
+++ b/gdb/python/py-breakpoint.c
@@ -637,8 +637,8 @@ bppy_get_ignore_count (PyObject *self, void *closure)
static int
bppy_init (PyObject *self, PyObject *args, PyObject *kwargs)
{
- static char *keywords[] = { "spec", "type", "wp_class", "internal",
- "temporary", NULL };
+ static const char *keywords[] = { "spec", "type", "wp_class", "internal",
+ "temporary", NULL };
const char *spec;
int type = bp_breakpoint;
int access_type = hw_write;
@@ -647,9 +647,9 @@ bppy_init (PyObject *self, PyObject *args, PyObject *kwargs)
int internal_bp = 0;
int temporary_bp = 0;

- if (! PyArg_ParseTupleAndKeywords (args, kwargs, "s|iiOO", keywords,
- &spec, &type, &access_type,
- &internal, &temporary))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kwargs, "s|iiOO", keywords,
+ &spec, &type, &access_type,
+ &internal, &temporary))
return -1;

if (internal)
diff --git a/gdb/python/py-cmd.c b/gdb/python/py-cmd.c
index 3aaf7f9..3e60673 100644
--- a/gdb/python/py-cmd.c
+++ b/gdb/python/py-cmd.c
@@ -490,8 +490,8 @@ cmdpy_init (PyObject *self, PyObject *args, PyObject *kw)
char *docstring = NULL;
struct cmd_list_element **cmd_list;
char *cmd_name, *pfx_name;
- static char *keywords[] = { "name", "command_class", "completer_class",
- "prefix", NULL };
+ static const char *keywords[] = { "name", "command_class", "completer_class",
+ "prefix", NULL };
PyObject *is_prefix = NULL;
int cmp;

@@ -504,9 +504,9 @@ cmdpy_init (PyObject *self, PyObject *args, PyObject *kw)
return -1;
}

- if (! PyArg_ParseTupleAndKeywords (args, kw, "si|iO",
- keywords, &name, &cmdtype,
- &completetype, &is_prefix))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "si|iO",
+ keywords, &name, &cmdtype,
+ &completetype, &is_prefix))
return -1;

if (cmdtype != no_class && cmdtype != class_run
diff --git a/gdb/python/py-finishbreakpoint.c b/gdb/python/py-finishbreakpoint.c
index 76189b8..06f6ff9 100644
--- a/gdb/python/py-finishbreakpoint.c
+++ b/gdb/python/py-finishbreakpoint.c
@@ -156,7 +156,7 @@ bpfinishpy_post_stop_hook (struct gdbpy_breakpoint_object *bp_obj)
static int
bpfinishpy_init (PyObject *self, PyObject *args, PyObject *kwargs)
{
- static char *keywords[] = { "frame", "internal", NULL };
+ static const char *keywords[] = { "frame", "internal", NULL };
struct finish_breakpoint_object *self_bpfinish =
(struct finish_breakpoint_object *) self;
PyObject *frame_obj = NULL;
@@ -169,8 +169,8 @@ bpfinishpy_init (PyObject *self, PyObject *args, PyObject *kwargs)
CORE_ADDR pc;
struct symbol *function;

- if (!PyArg_ParseTupleAndKeywords (args, kwargs, "|OO", keywords,
- &frame_obj, &internal))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kwargs, "|OO", keywords,
+ &frame_obj, &internal))
return -1;

TRY
diff --git a/gdb/python/py-inferior.c b/gdb/python/py-inferior.c
index 77fc543..41bedb5 100644
--- a/gdb/python/py-inferior.c
+++ b/gdb/python/py-inferior.c
@@ -435,10 +435,10 @@ infpy_read_memory (PyObject *self, PyObject *args, PyObject *kw)
CORE_ADDR addr, length;
gdb_byte *buffer = NULL;
PyObject *addr_obj, *length_obj, *result;
- static char *keywords[] = { "address", "length", NULL };
+ static const char *keywords[] = { "address", "length", NULL };

- if (! PyArg_ParseTupleAndKeywords (args, kw, "OO", keywords,
- &addr_obj, &length_obj))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "OO", keywords,
+ &addr_obj, &length_obj))
return NULL;

if (get_addr_from_python (addr_obj, &addr) < 0
@@ -494,13 +494,12 @@ infpy_write_memory (PyObject *self, PyObject *args, PyObject *kw)
const gdb_byte *buffer;
CORE_ADDR addr, length;
PyObject *addr_obj, *length_obj = NULL;
- static char *keywords[] = { "address", "buffer", "length", NULL };
+ static const char *keywords[] = { "address", "buffer", "length", NULL };
#ifdef IS_PY3K
Py_buffer pybuf;

- if (! PyArg_ParseTupleAndKeywords (args, kw, "Os*|O", keywords,
- &addr_obj, &pybuf,
- &length_obj))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "Os*|O", keywords,
+ &addr_obj, &pybuf, &length_obj))
return NULL;

buffer = (const gdb_byte *) pybuf.buf;
@@ -643,7 +642,7 @@ infpy_search_memory (PyObject *self, PyObject *args, PyObject *kw)
{
struct gdb_exception except = exception_none;
CORE_ADDR start_addr, length;
- static char *keywords[] = { "address", "length", "pattern", NULL };
+ static const char *keywords[] = { "address", "length", "pattern", NULL };
PyObject *start_addr_obj, *length_obj;
Py_ssize_t pattern_size;
const gdb_byte *buffer;
@@ -652,9 +651,9 @@ infpy_search_memory (PyObject *self, PyObject *args, PyObject *kw)
#ifdef IS_PY3K
Py_buffer pybuf;

- if (! PyArg_ParseTupleAndKeywords (args, kw, "OOs*", keywords,
- &start_addr_obj, &length_obj,
- &pybuf))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "OOs*", keywords,
+ &start_addr_obj, &length_obj,
+ &pybuf))
return NULL;

buffer = (const gdb_byte *) pybuf.buf;
diff --git a/gdb/python/py-objfile.c b/gdb/python/py-objfile.c
index 6a47c17..52f2e1f 100644
--- a/gdb/python/py-objfile.c
+++ b/gdb/python/py-objfile.c
@@ -432,13 +432,13 @@ objfpy_is_valid (PyObject *self, PyObject *args)
static PyObject *
objfpy_add_separate_debug_file (PyObject *self, PyObject *args, PyObject *kw)
{
- static char *keywords[] = { "file_name", NULL };
+ static const char *keywords[] = { "file_name", NULL };
objfile_object *obj = (objfile_object *) self;
const char *file_name;

OBJFPY_REQUIRE_VALID (obj);

- if (!PyArg_ParseTupleAndKeywords (args, kw, "s", keywords, &file_name))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "s", keywords, &file_name))
return NULL;

TRY
@@ -559,14 +559,14 @@ objfpy_lookup_objfile_by_build_id (const char *build_id)
PyObject *
gdbpy_lookup_objfile (PyObject *self, PyObject *args, PyObject *kw)
{
- static char *keywords[] = { "name", "by_build_id", NULL };
+ static const char *keywords[] = { "name", "by_build_id", NULL };
const char *name;
PyObject *by_build_id_obj = NULL;
int by_build_id;
struct objfile *objfile;

- if (! PyArg_ParseTupleAndKeywords (args, kw, "s|O!", keywords,
- &name, &PyBool_Type, &by_build_id_obj))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "s|O!", keywords,
+ &name, &PyBool_Type, &by_build_id_obj))
return NULL;

by_build_id = 0;
diff --git a/gdb/python/py-symbol.c b/gdb/python/py-symbol.c
index 05b002f..c9f83a3 100644
--- a/gdb/python/py-symbol.c
+++ b/gdb/python/py-symbol.c
@@ -373,13 +373,14 @@ gdbpy_lookup_symbol (PyObject *self, PyObject *args, PyObject *kw)
int domain = VAR_DOMAIN;
struct field_of_this_result is_a_field_of_this;
const char *name;
- static char *keywords[] = { "name", "block", "domain", NULL };
+ static const char *keywords[] = { "name", "block", "domain", NULL };
struct symbol *symbol = NULL;
PyObject *block_obj = NULL, *sym_obj, *bool_obj;
const struct block *block = NULL;

- if (! PyArg_ParseTupleAndKeywords (args, kw, "s|O!i", keywords, &name,
- &block_object_type, &block_obj, &domain))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "s|O!i", keywords, &name,
+ &block_object_type, &block_obj,
+ &domain))
return NULL;

if (block_obj)
@@ -443,12 +444,12 @@ gdbpy_lookup_global_symbol (PyObject *self, PyObject *args, PyObject *kw)
{
int domain = VAR_DOMAIN;
const char *name;
- static char *keywords[] = { "name", "domain", NULL };
+ static const char *keywords[] = { "name", "domain", NULL };
struct symbol *symbol = NULL;
PyObject *sym_obj;

- if (! PyArg_ParseTupleAndKeywords (args, kw, "s|i", keywords, &name,
- &domain))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "s|i", keywords, &name,
+ &domain))
return NULL;

TRY
diff --git a/gdb/python/py-type.c b/gdb/python/py-type.c
index 12b6310..aa20d4c 100644
--- a/gdb/python/py-type.c
+++ b/gdb/python/py-type.c
@@ -1347,14 +1347,14 @@ type_object_to_type (PyObject *obj)
PyObject *
gdbpy_lookup_type (PyObject *self, PyObject *args, PyObject *kw)
{
- static char *keywords[] = { "name", "block", NULL };
+ static const char *keywords[] = { "name", "block", NULL };
const char *type_name = NULL;
struct type *type = NULL;
PyObject *block_obj = NULL;
const struct block *block = NULL;

- if (! PyArg_ParseTupleAndKeywords (args, kw, "s|O", keywords,
- &type_name, &block_obj))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "s|O", keywords,
+ &type_name, &block_obj))
return NULL;

if (block_obj)
diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
index 9c0470f..b5a0ef8 100644
--- a/gdb/python/py-value.c
+++ b/gdb/python/py-value.c
@@ -431,11 +431,11 @@ valpy_lazy_string (PyObject *self, PyObject *args, PyObject *kw)
gdb_py_longest length = -1;
struct value *value = ((value_object *) self)->value;
const char *user_encoding = NULL;
- static char *keywords[] = { "encoding", "length", NULL };
+ static const char *keywords[] = { "encoding", "length", NULL };
PyObject *str_obj = NULL;

- if (!PyArg_ParseTupleAndKeywords (args, kw, "|s" GDB_PY_LL_ARG, keywords,
- &user_encoding, &length))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "|s" GDB_PY_LL_ARG,
+ keywords, &user_encoding, &length))
return NULL;

if (length < -1)
@@ -526,10 +526,10 @@ valpy_string (PyObject *self, PyObject *args, PyObject *kw)
const char *user_encoding = NULL;
const char *la_encoding = NULL;
struct type *char_type;
- static char *keywords[] = { "encoding", "errors", "length", NULL };
+ static const char *keywords[] = { "encoding", "errors", "length", NULL };

- if (!PyArg_ParseTupleAndKeywords (args, kw, "|ssi", keywords,
- &user_encoding, &errors, &length))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "|ssi", keywords,
+ &user_encoding, &errors, &length))
return NULL;

TRY
diff --git a/gdb/python/python-internal.h b/gdb/python/python-internal.h
index d4ed170..db75002 100644
--- a/gdb/python/python-internal.h
+++ b/gdb/python/python-internal.h
@@ -316,6 +316,34 @@ struct gdb_PyGetSetDef : PyGetSetDef
{}
};

+/* The 'keywords' parameter of PyArg_ParseTupleAndKeywords has type
+ 'char **'. However, string literals are const in C++, and so to
+ avoid casting at every keyword array definition, we'll need to make
+ the keywords array an array of 'const char *'. To avoid having all
+ callers add a 'const_cast<char **>' themselves when passing such an
+ array through 'char **', we define our own version of
+ PyArg_ParseTupleAndKeywords here with a corresponding 'keywords'
+ parameter type that does the cast in a single place. (This is not
+ an overload of PyArg_ParseTupleAndKeywords in order to make it
+ clearer that we're calling our own function instead of a function
+ that exists in some newer Python version.) */
+
+static inline int
+gdb_PyArg_ParseTupleAndKeywords (PyObject *args, PyObject *kw,
+ const char *format, const char **keywords, ...)
+{
+ va_list ap;
+ int res;
+
+ va_start (ap, keywords);
+ res = PyArg_VaParseTupleAndKeywords (args, kw, format,
+ const_cast<char **> (keywords),
+ ap);
+ va_end (ap);
+
+ return res;
+}
+
/* In order to be able to parse symtab_and_line_to_sal_object function
a real symtab_and_line structure is needed. */
#include "symtab.h"
diff --git a/gdb/python/python.c b/gdb/python/python.c
index a7aff53..25f475f 100644
--- a/gdb/python/python.c
+++ b/gdb/python/python.c
@@ -572,11 +572,11 @@ execute_gdb_command (PyObject *self, PyObject *args, PyObject *kw)
const char *arg;
PyObject *from_tty_obj = NULL, *to_string_obj = NULL;
int from_tty, to_string;
- static char *keywords[] = {"command", "from_tty", "to_string", NULL };
+ static const char *keywords[] = { "command", "from_tty", "to_string", NULL };

- if (! PyArg_ParseTupleAndKeywords (args, kw, "s|O!O!", keywords, &arg,
- &PyBool_Type, &from_tty_obj,
- &PyBool_Type, &to_string_obj))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "s|O!O!", keywords, &arg,
+ &PyBool_Type, &from_tty_obj,
+ &PyBool_Type, &to_string_obj))
return NULL;

from_tty = 0;
@@ -1047,11 +1047,11 @@ static PyObject *
gdbpy_write (PyObject *self, PyObject *args, PyObject *kw)
{
const char *arg;
- static char *keywords[] = {"text", "stream", NULL };
+ static const char *keywords[] = { "text", "stream", NULL };
int stream_type = 0;

- if (! PyArg_ParseTupleAndKeywords (args, kw, "s|i", keywords, &arg,
- &stream_type))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "s|i", keywords, &arg,
+ &stream_type))
return NULL;

TRY
@@ -1088,11 +1088,11 @@ gdbpy_write (PyObject *self, PyObject *args, PyObject *kw)
static PyObject *
gdbpy_flush (PyObject *self, PyObject *args, PyObject *kw)
{
- static char *keywords[] = {"stream", NULL };
+ static const char *keywords[] = { "stream", NULL };
int stream_type = 0;

- if (! PyArg_ParseTupleAndKeywords (args, kw, "|i", keywords,
- &stream_type))
+ if (!gdb_PyArg_ParseTupleAndKeywords (args, kw, "|i", keywords,
+ &stream_type))
return NULL;

switch (stream_type)
--
2.5.5