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binutils-gdb/gdb/python/py-prettyprint.c
Andrew Burgess 2e62ab400f gdb: Introduce 'print max-depth' feature 
Introduce a new print setting max-depth which can be set with 'set
print max-depth DEPTH'.  The default value of DEPTH is 20, but this
can also be set to unlimited.

When GDB is printing a value containing nested structures GDB will
stop descending at depth DEPTH.  Here is a small example:

    typedef struct s1 { int a; } s1;
    typedef struct s2 { s1 b; } s2;
    typedef struct s3 { s2 c; } s3;
    typedef struct s4 { s3 d; } s4;

    s4 var = { { { { 3 } } } };

The following table shows how various depth settings affect printing
of 'var':

    | Depth Setting | Result of 'p var'              |
    |---------------+--------------------------------|
    |     Unlimited | $1 = {d = {c = {b = {a = 3}}}} |
    |             4 | $1 = {d = {c = {b = {a = 3}}}} |
    |             3 | $1 = {d = {c = {b = {...}}}}   |
    |             2 | $1 = {d = {c = {...}}}         |
    |             1 | $1 = {d = {...}}               |
    |             0 | $1 = {...}                     |

Only structures, unions, and arrays are replaced in this way, scalars
and strings are not replaced.

The replacement is counted from the level at which you print, not from
the top level of the structure.  So, consider the above example and
this GDB session:

    (gdb) set print max-depth 2
    (gdb) p var
    $1 = {d = {c = {...}}}
    (gdb) p var.d
    $2 = {c = {b = {...}}}
    (gdb) p var.d.c
    $3 = {b = {a = 3}}

Setting the max-depth to 2 doesn't prevent the user from exploring
deeper into 'var' by asking for specific sub-fields to be printed.

The motivation behind this feature is to try and give the user more
control over how much is printed when examining large, complex data
structures.

The default max-depth of 20 means that there is a change in GDB's
default behaviour.  Someone printing a data structure with 20 levels
of nesting will now see '{...}' instead of their data, they would need
to adjust the max depth, or call print again naming a specific field
in order to dig deeper into their data structure.  If this is
considered a problem then we could increase the default, or even make
the default unlimited.

This commit relies on the previous commit, which added a new field to
the language structure, this new field was a string that contained the
pattern that should be used when a structure/union/array is replaced
in the output, this allows languages to use a syntax that is more
appropriate, mostly this will be selecting the correct types of
bracket '(...)' or '{...}', both of which are currently in use.

This commit should have no impact on MI output, expressions are
printed through the MI using -var-create and then -var-list-children.
As each use of -var-list-children only ever displays a single level of
an expression then the max-depth setting will have no impact.

This commit also adds the max-depth mechanism to the scripting
language pretty printers following basically the same rules as for the
built in value printing.

One quirk is that when printing a value using the display hint 'map',
if the keys of the map are structs then GDB will hide the keys one
depth level after it hides the values, this ensures that GDB produces
output like this:

  $1 = map_object = {[{key1}] = {...}, [{key2}] = {...}}

Instead of this less helpful output:

  $1 = map_object = {[{...}] = {...}, [{...}] = {...}}

This is covered by the new tests in gdb.python/py-nested-maps.exp.

gdb/ChangeLog:

	* cp-valprint.c (cp_print_value_fields): Allow an additional level
	of depth when printing anonymous structs or unions.
	* guile/scm-pretty-print.c (gdbscm_apply_val_pretty_printer):
	Don't print either the top-level value, or the children if the
	max-depth is exceeded.
	(ppscm_print_children): When printing the key of a map, allow one
	extra level of depth.
	* python/py-prettyprint.c (gdbpy_apply_val_pretty_printer): Don't
	print either the top-level value, or the children if the max-depth
	is exceeded.
	(print_children): When printing the key of a map, allow one extra
	level of depth.
	* python/py-value.c (valpy_format_string): Add max_depth keyword.
	* valprint.c: (PRINT_MAX_DEPTH_DEFAULT): Define.
	(user_print_options): Initialise max_depth field.
	(val_print_scalar_or_string_type_p): New function.
	(val_print): Check to see if the max depth has been reached.
	(val_print_check_max_depth): Define new function.
	(show_print_max_depth): New function.
	(_initialize_valprint): Add 'print max-depth' option.
	* valprint.h (struct value_print_options) <max_depth>: New field.
	(val_print_check_max_depth): Declare new function.
	* NEWS: Document new feature.

gdb/doc/ChangeLog:

	* gdb.texinfo (Print Settings): Document 'print max-depth'.
	* guile.texi (Guile Pretty Printing API): Document that 'print
	max-depth' can effect the display of a values children.
	* python.texi (Pretty Printing API): Likewise.
	(Values From Inferior): Document max_depth keyword.

gdb/testsuite/ChangeLog:

	* gdb.base/max-depth.c: New file.
	* gdb.base/max-depth.exp: New file.
	* gdb.python/py-nested-maps.c: New file.
	* gdb.python/py-nested-maps.exp: New file.
	* gdb.python/py-nested-maps.py: New file.
	* gdb.python/py-format-string.exp (test_max_depth): New proc.
	(test_all_common): Call test_max_depth.
	* gdb.fortran/max-depth.exp: New file.
	* gdb.fortran/max-depth.f90: New file.
	* gdb.go/max-depth.exp: New file.
	* gdb.go/max-depth.go: New file.
	* gdb.modula2/max-depth.exp: New file.
	* gdb.modula2/max-depth.c: New file.
	* lib/gdb.exp (get_print_expr_at_depths): New proc.
2019-04-29 22:01:09 +01:00

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/* Python pretty-printing
Copyright (C) 2008-2019 Free Software Foundation, Inc.
This file is part of GDB.
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/>. */
#include "defs.h"
#include "objfiles.h"
#include "symtab.h"
#include "language.h"
#include "valprint.h"
#include "extension-priv.h"
#include "python.h"
#include "python-internal.h"
/* Return type of print_string_repr. */
enum string_repr_result
{
/* The string method returned None. */
string_repr_none,
/* The string method had an error. */
string_repr_error,
/* Everything ok. */
string_repr_ok
};
/* Helper function for find_pretty_printer which iterates over a list,
calls each function and inspects output. This will return a
printer object if one recognizes VALUE. If no printer is found, it
will return None. On error, it will set the Python error and
return NULL. */
static gdbpy_ref<>
search_pp_list (PyObject *list, PyObject *value)
{
Py_ssize_t pp_list_size, list_index;
pp_list_size = PyList_Size (list);
for (list_index = 0; list_index < pp_list_size; list_index++)
{
PyObject *function = PyList_GetItem (list, list_index);
if (! function)
return NULL;
/* Skip if disabled. */
if (PyObject_HasAttr (function, gdbpy_enabled_cst))
{
gdbpy_ref<> attr (PyObject_GetAttr (function, gdbpy_enabled_cst));
int cmp;
if (attr == NULL)
return NULL;
cmp = PyObject_IsTrue (attr.get ());
if (cmp == -1)
return NULL;
if (!cmp)
continue;
}
gdbpy_ref<> printer (PyObject_CallFunctionObjArgs (function, value,
NULL));
if (printer == NULL)
return NULL;
else if (printer != Py_None)
return printer;
}
return gdbpy_ref<>::new_reference (Py_None);
}
/* Subroutine of find_pretty_printer to simplify it.
Look for a pretty-printer to print VALUE in all objfiles.
The result is NULL if there's an error and the search should be terminated.
The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
Otherwise the result is the pretty-printer function, suitably inc-ref'd. */
static PyObject *
find_pretty_printer_from_objfiles (PyObject *value)
{
for (objfile *obj : current_program_space->objfiles ())
{
gdbpy_ref<> objf = objfile_to_objfile_object (obj);
if (objf == NULL)
{
/* Ignore the error and continue. */
PyErr_Clear ();
continue;
}
gdbpy_ref<> pp_list (objfpy_get_printers (objf.get (), NULL));
gdbpy_ref<> function (search_pp_list (pp_list.get (), value));
/* If there is an error in any objfile list, abort the search and exit. */
if (function == NULL)
return NULL;
if (function != Py_None)
return function.release ();
}
Py_RETURN_NONE;
}
/* Subroutine of find_pretty_printer to simplify it.
Look for a pretty-printer to print VALUE in the current program space.
The result is NULL if there's an error and the search should be terminated.
The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
Otherwise the result is the pretty-printer function, suitably inc-ref'd. */
static gdbpy_ref<>
find_pretty_printer_from_progspace (PyObject *value)
{
gdbpy_ref<> obj = pspace_to_pspace_object (current_program_space);
if (obj == NULL)
return NULL;
gdbpy_ref<> pp_list (pspy_get_printers (obj.get (), NULL));
return search_pp_list (pp_list.get (), value);
}
/* Subroutine of find_pretty_printer to simplify it.
Look for a pretty-printer to print VALUE in the gdb module.
The result is NULL if there's an error and the search should be terminated.
The result is Py_None, suitably inc-ref'd, if no pretty-printer was found.
Otherwise the result is the pretty-printer function, suitably inc-ref'd. */
static gdbpy_ref<>
find_pretty_printer_from_gdb (PyObject *value)
{
/* Fetch the global pretty printer list. */
if (gdb_python_module == NULL
|| ! PyObject_HasAttrString (gdb_python_module, "pretty_printers"))
return gdbpy_ref<>::new_reference (Py_None);
gdbpy_ref<> pp_list (PyObject_GetAttrString (gdb_python_module,
"pretty_printers"));
if (pp_list == NULL || ! PyList_Check (pp_list.get ()))
return gdbpy_ref<>::new_reference (Py_None);
return search_pp_list (pp_list.get (), value);
}
/* Find the pretty-printing constructor function for VALUE. If no
pretty-printer exists, return None. If one exists, return a new
reference. On error, set the Python error and return NULL. */
static gdbpy_ref<>
find_pretty_printer (PyObject *value)
{
/* Look at the pretty-printer list for each objfile
in the current program-space. */
gdbpy_ref<> function (find_pretty_printer_from_objfiles (value));
if (function == NULL || function != Py_None)
return function;
/* Look at the pretty-printer list for the current program-space. */
function = find_pretty_printer_from_progspace (value);
if (function == NULL || function != Py_None)
return function;
/* Look at the pretty-printer list in the gdb module. */
return find_pretty_printer_from_gdb (value);
}
/* Pretty-print a single value, via the printer object PRINTER.
If the function returns a string, a PyObject containing the string
is returned. If the function returns Py_NONE that means the pretty
printer returned the Python None as a value. Otherwise, if the
function returns a value, *OUT_VALUE is set to the value, and NULL
is returned. On error, *OUT_VALUE is set to NULL, NULL is
returned, with a python exception set. */
static gdbpy_ref<>
pretty_print_one_value (PyObject *printer, struct value **out_value)
{
gdbpy_ref<> result;
*out_value = NULL;
try
{
if (!PyObject_HasAttr (printer, gdbpy_to_string_cst))
result = gdbpy_ref<>::new_reference (Py_None);
else
{
result.reset (PyObject_CallMethodObjArgs (printer, gdbpy_to_string_cst,
NULL));
if (result != NULL)
{
if (! gdbpy_is_string (result.get ())
&& ! gdbpy_is_lazy_string (result.get ())
&& result != Py_None)
{
*out_value = convert_value_from_python (result.get ());
if (PyErr_Occurred ())
*out_value = NULL;
result = NULL;
}
}
}
}
catch (const gdb_exception &except)
{
}
return result;
}
/* Return the display hint for the object printer, PRINTER. Return
NULL if there is no display_hint method, or if the method did not
return a string. On error, print stack trace and return NULL. On
success, return an xmalloc()d string. */
gdb::unique_xmalloc_ptr<char>
gdbpy_get_display_hint (PyObject *printer)
{
gdb::unique_xmalloc_ptr<char> result;
if (! PyObject_HasAttr (printer, gdbpy_display_hint_cst))
return NULL;
gdbpy_ref<> hint (PyObject_CallMethodObjArgs (printer, gdbpy_display_hint_cst,
NULL));
if (hint != NULL)
{
if (gdbpy_is_string (hint.get ()))
{
result = python_string_to_host_string (hint.get ());
if (result == NULL)
gdbpy_print_stack ();
}
}
else
gdbpy_print_stack ();
return result;
}
/* A wrapper for gdbpy_print_stack that ignores MemoryError. */
static void
print_stack_unless_memory_error (struct ui_file *stream)
{
if (PyErr_ExceptionMatches (gdbpy_gdb_memory_error))
{
gdbpy_err_fetch fetched_error;
gdb::unique_xmalloc_ptr<char> msg = fetched_error.to_string ();
if (msg == NULL || *msg == '\0')
fprintf_filtered (stream, _("<error reading variable>"));
else
fprintf_filtered (stream, _("<error reading variable: %s>"),
msg.get ());
}
else
gdbpy_print_stack ();
}
/* Helper for gdbpy_apply_val_pretty_printer which calls to_string and
formats the result. */
static enum string_repr_result
print_string_repr (PyObject *printer, const char *hint,
struct ui_file *stream, int recurse,
const struct value_print_options *options,
const struct language_defn *language,
struct gdbarch *gdbarch)
{
struct value *replacement = NULL;
enum string_repr_result result = string_repr_ok;
gdbpy_ref<> py_str = pretty_print_one_value (printer, &replacement);
if (py_str != NULL)
{
if (py_str == Py_None)
result = string_repr_none;
else if (gdbpy_is_lazy_string (py_str.get ()))
{
CORE_ADDR addr;
long length;
struct type *type;
gdb::unique_xmalloc_ptr<char> encoding;
struct value_print_options local_opts = *options;
gdbpy_extract_lazy_string (py_str.get (), &addr, &type,
&length, &encoding);
local_opts.addressprint = 0;
val_print_string (type, encoding.get (), addr, (int) length,
stream, &local_opts);
}
else
{
gdbpy_ref<> string
= python_string_to_target_python_string (py_str.get ());
if (string != NULL)
{
char *output;
long length;
struct type *type;
output = PyBytes_AS_STRING (string.get ());
length = PyBytes_GET_SIZE (string.get ());
type = builtin_type (gdbarch)->builtin_char;
if (hint && !strcmp (hint, "string"))
LA_PRINT_STRING (stream, type, (gdb_byte *) output,
length, NULL, 0, options);
else
fputs_filtered (output, stream);
}
else
{
result = string_repr_error;
print_stack_unless_memory_error (stream);
}
}
}
else if (replacement)
{
struct value_print_options opts = *options;
opts.addressprint = 0;
common_val_print (replacement, stream, recurse, &opts, language);
}
else
{
result = string_repr_error;
print_stack_unless_memory_error (stream);
}
return result;
}
/* Helper for gdbpy_apply_val_pretty_printer that formats children of the
printer, if any exist. If is_py_none is true, then nothing has
been printed by to_string, and format output accordingly. */
static void
print_children (PyObject *printer, const char *hint,
struct ui_file *stream, int recurse,
const struct value_print_options *options,
const struct language_defn *language,
int is_py_none)
{
int is_map, is_array, done_flag, pretty;
unsigned int i;
if (! PyObject_HasAttr (printer, gdbpy_children_cst))
return;
/* If we are printing a map or an array, we want some special
formatting. */
is_map = hint && ! strcmp (hint, "map");
is_array = hint && ! strcmp (hint, "array");
gdbpy_ref<> children (PyObject_CallMethodObjArgs (printer, gdbpy_children_cst,
NULL));
if (children == NULL)
{
print_stack_unless_memory_error (stream);
return;
}
gdbpy_ref<> iter (PyObject_GetIter (children.get ()));
if (iter == NULL)
{
print_stack_unless_memory_error (stream);
return;
}
/* Use the prettyformat_arrays option if we are printing an array,
and the pretty option otherwise. */
if (is_array)
pretty = options->prettyformat_arrays;
else
{
if (options->prettyformat == Val_prettyformat)
pretty = 1;
else
pretty = options->prettyformat_structs;
}
done_flag = 0;
for (i = 0; i < options->print_max; ++i)
{
PyObject *py_v;
const char *name;
gdbpy_ref<> item (PyIter_Next (iter.get ()));
if (item == NULL)
{
if (PyErr_Occurred ())
print_stack_unless_memory_error (stream);
/* Set a flag so we can know whether we printed all the
available elements. */
else
done_flag = 1;
break;
}
if (! PyTuple_Check (item.get ()) || PyTuple_Size (item.get ()) != 2)
{
PyErr_SetString (PyExc_TypeError,
_("Result of children iterator not a tuple"
" of two elements."));
gdbpy_print_stack ();
continue;
}
if (! PyArg_ParseTuple (item.get (), "sO", &name, &py_v))
{
/* The user won't necessarily get a stack trace here, so provide
more context. */
if (gdbpy_print_python_errors_p ())
fprintf_unfiltered (gdb_stderr,
_("Bad result from children iterator.\n"));
gdbpy_print_stack ();
continue;
}
/* Print initial "{". For other elements, there are three
cases:
1. Maps. Print a "," after each value element.
2. Arrays. Always print a ",".
3. Other. Always print a ",". */
if (i == 0)
{
if (is_py_none)
fputs_filtered ("{", stream);
else
fputs_filtered (" = {", stream);
}
else if (! is_map || i % 2 == 0)
fputs_filtered (pretty ? "," : ", ", stream);
/* In summary mode, we just want to print "= {...}" if there is
a value. */
if (options->summary)
{
/* This increment tricks the post-loop logic to print what
we want. */
++i;
/* Likewise. */
pretty = 0;
break;
}
if (! is_map || i % 2 == 0)
{
if (pretty)
{
fputs_filtered ("\n", stream);
print_spaces_filtered (2 + 2 * recurse, stream);
}
else
wrap_here (n_spaces (2 + 2 *recurse));
}
if (is_map && i % 2 == 0)
fputs_filtered ("[", stream);
else if (is_array)
{
/* We print the index, not whatever the child method
returned as the name. */
if (options->print_array_indexes)
fprintf_filtered (stream, "[%d] = ", i);
}
else if (! is_map)
{
fputs_filtered (name, stream);
fputs_filtered (" = ", stream);
}
if (gdbpy_is_lazy_string (py_v))
{
CORE_ADDR addr;
struct type *type;
long length;
gdb::unique_xmalloc_ptr<char> encoding;
struct value_print_options local_opts = *options;
gdbpy_extract_lazy_string (py_v, &addr, &type, &length, &encoding);
local_opts.addressprint = 0;
val_print_string (type, encoding.get (), addr, (int) length, stream,
&local_opts);
}
else if (gdbpy_is_string (py_v))
{
gdb::unique_xmalloc_ptr<char> output;
output = python_string_to_host_string (py_v);
if (!output)
gdbpy_print_stack ();
else
fputs_filtered (output.get (), stream);
}
else
{
struct value *value = convert_value_from_python (py_v);
if (value == NULL)
{
gdbpy_print_stack ();
error (_("Error while executing Python code."));
}
else
{
/* When printing the key of a map we allow one additional
level of depth. This means the key will print before the
value does. */
struct value_print_options opt = *options;
if (is_map && i % 2 == 0
&& opt.max_depth != -1
&& opt.max_depth < INT_MAX)
++opt.max_depth;
common_val_print (value, stream, recurse + 1, &opt, language);
}
}
if (is_map && i % 2 == 0)
fputs_filtered ("] = ", stream);
}
if (i)
{
if (!done_flag)
{
if (pretty)
{
fputs_filtered ("\n", stream);
print_spaces_filtered (2 + 2 * recurse, stream);
}
fputs_filtered ("...", stream);
}
if (pretty)
{
fputs_filtered ("\n", stream);
print_spaces_filtered (2 * recurse, stream);
}
fputs_filtered ("}", stream);
}
}
enum ext_lang_rc
gdbpy_apply_val_pretty_printer (const struct extension_language_defn *extlang,
struct type *type,
LONGEST embedded_offset, CORE_ADDR address,
struct ui_file *stream, int recurse,
struct value *val,
const struct value_print_options *options,
const struct language_defn *language)
{
struct gdbarch *gdbarch = get_type_arch (type);
struct value *value;
enum string_repr_result print_result;
if (value_lazy (val))
value_fetch_lazy (val);
/* No pretty-printer support for unavailable values. */
if (!value_bytes_available (val, embedded_offset, TYPE_LENGTH (type)))
return EXT_LANG_RC_NOP;
if (!gdb_python_initialized)
return EXT_LANG_RC_NOP;
gdbpy_enter enter_py (gdbarch, language);
/* Instantiate the printer. */
value = value_from_component (val, type, embedded_offset);
gdbpy_ref<> val_obj (value_to_value_object (value));
if (val_obj == NULL)
{
print_stack_unless_memory_error (stream);
return EXT_LANG_RC_ERROR;
}
/* Find the constructor. */
gdbpy_ref<> printer (find_pretty_printer (val_obj.get ()));
if (printer == NULL)
{
print_stack_unless_memory_error (stream);
return EXT_LANG_RC_ERROR;
}
if (printer == Py_None)
return EXT_LANG_RC_NOP;
if (val_print_check_max_depth (stream, recurse, options, language))
return EXT_LANG_RC_OK;
/* If we are printing a map, we want some special formatting. */
gdb::unique_xmalloc_ptr<char> hint (gdbpy_get_display_hint (printer.get ()));
/* Print the section */
print_result = print_string_repr (printer.get (), hint.get (), stream,
recurse, options, language, gdbarch);
if (print_result != string_repr_error)
print_children (printer.get (), hint.get (), stream, recurse, options,
language, print_result == string_repr_none);
if (PyErr_Occurred ())
print_stack_unless_memory_error (stream);
return EXT_LANG_RC_OK;
}
/* Apply a pretty-printer for the varobj code. PRINTER_OBJ is the
print object. It must have a 'to_string' method (but this is
checked by varobj, not here) which takes no arguments and
returns a string. The printer will return a value and in the case
of a Python string being returned, this function will return a
PyObject containing the string. For any other type, *REPLACEMENT is
set to the replacement value and this function returns NULL. On
error, *REPLACEMENT is set to NULL and this function also returns
NULL. */
gdbpy_ref<>
apply_varobj_pretty_printer (PyObject *printer_obj,
struct value **replacement,
struct ui_file *stream)
{
*replacement = NULL;
gdbpy_ref<> py_str = pretty_print_one_value (printer_obj, replacement);
if (*replacement == NULL && py_str == NULL)
print_stack_unless_memory_error (stream);
return py_str;
}
/* Find a pretty-printer object for the varobj module. Returns a new
reference to the object if successful; returns NULL if not. VALUE
is the value for which a printer tests to determine if it
can pretty-print the value. */
gdbpy_ref<>
gdbpy_get_varobj_pretty_printer (struct value *value)
{
try
{
value = value_copy (value);
}
catch (const gdb_exception &except)
{
GDB_PY_HANDLE_EXCEPTION (except);
}
gdbpy_ref<> val_obj (value_to_value_object (value));
if (val_obj == NULL)
return NULL;
return find_pretty_printer (val_obj.get ());
}
/* A Python function which wraps find_pretty_printer and instantiates
the resulting class. This accepts a Value argument and returns a
pretty printer instance, or None. This function is useful as an
argument to the MI command -var-set-visualizer. */
PyObject *
gdbpy_default_visualizer (PyObject *self, PyObject *args)
{
PyObject *val_obj;
struct value *value;
if (! PyArg_ParseTuple (args, "O", &val_obj))
return NULL;
value = value_object_to_value (val_obj);
if (! value)
{
PyErr_SetString (PyExc_TypeError,
_("Argument must be a gdb.Value."));
return NULL;
}
return find_pretty_printer (val_obj).release ();
}
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