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gdb: fix getting range of flexible array member in Python

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As reported in bug 27757, we get an internal error when doing:

    $ cat test.c
    struct foo {
        int len;
        int items[];
    };

    struct foo *p;

    int main() {
        return 0;
    }
    $ gcc test.c -g -O0 -o test
    $ ./gdb -q -nx --data-directory=data-directory ./test -ex 'python gdb.parse_and_eval("p").type.target()["items"].type.range()'
    Reading symbols from ./test...
    /home/simark/src/binutils-gdb/gdb/gdbtypes.h:435: internal-error: LONGEST dynamic_prop::const_val() const: Assertion `m_kind == PROP_CONST' failed.
    A problem internal to GDB has been detected,
    further debugging may prove unreliable.
    Quit this debugging session? (y or n)

This is because the Python code (typy_range) blindly reads the high
bound of the type of `items` as a constant value.  Since it is a
flexible array member, it has no high bound, the property is undefined.
Since commit 8c2e4e0689 ("gdb: add accessors to struct dynamic_prop"),
the getters check that you are not getting a property value of the wrong
kind, so this causes a failed assertion.

Fix it by checking if the property is indeed a constant value before
accessing it as such.  Otherwise, use 0.  This restores the previous GDB
behavior: because the structure was zero-initialized, this is what was
returned before.  But now this behavior is explicit and not accidental.

Add a test, gdb.python/flexible-array-member.exp, that is derived from
gdb.base/flexible-array-member.exp.  It tests the same things, but
through the Python API.  It also specifically tests getting the range
from the various kinds of flexible array member types (AFAIK it wasn't
possible to do the equivalent through the CLI).

gdb/ChangeLog:

	PR gdb/27757
	* python/py-type.c (typy_range): Check that bounds are constant
	before accessing them as such.
	* guile/scm-type.c (gdbscm_type_range): Likewise.

gdb/testsuite/ChangeLog:

	PR gdb/27757
	* gdb.python/flexible-array-member.c: New test.
	* gdb.python/flexible-array-member.exp: New test.
	* gdb.guile/scm-type.exp (test_range): Add test for flexible
	array member.
	* gdb.guile/scm-type.c (struct flex_member): New.
	(main): Use it.

Change-Id: Ibef92ee5fd871ecb7c791db2a788f203dff2b841
This commit is contained in:
Simon Marchi 2021-04-22 15:01:28 -04:00
parent 2f63213381
commit e25d6d93c4
8 changed files with 210 additions and 4 deletions
Download patch file Download diff file Expand all files Collapse all files

7
gdb/ChangeLog
View file

@ -1,3 +1,10 @@
2021-04-22 Simon Marchi <simon.marchi@polymtl.ca>
PR gdb/27757
* python/py-type.c (typy_range): Check that bounds are constant
before accessing them as such.
* guile/scm-type.c (gdbscm_type_range): Likewise.
2021-04-22 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
* Makefile.in (COMMON_SFILES): Remove continuations.c.

11
gdb/guile/scm-type.c
View file

@ -823,8 +823,15 @@ gdbscm_type_range (SCM self)
case TYPE_CODE_ARRAY:
case TYPE_CODE_STRING:
case TYPE_CODE_RANGE:
low = type->bounds ()->low.const_val ();
high = type->bounds ()->high.const_val ();
if (type->bounds ()->low.kind () == PROP_CONST)
low = type->bounds ()->low.const_val ();
else
low = 0;
if (type->bounds ()->high.kind () == PROP_CONST)
high = type->bounds ()->high.const_val ();
else
high = 0;
break;
}

11
gdb/python/py-type.c
View file

@ -592,8 +592,15 @@ typy_range (PyObject *self, PyObject *args)
case TYPE_CODE_ARRAY:
case TYPE_CODE_STRING:
case TYPE_CODE_RANGE:
low = type->bounds ()->low.const_val ();
high = type->bounds ()->high.const_val ();;
if (type->bounds ()->low.kind () == PROP_CONST)
low = type->bounds ()->low.const_val ();
else
low = 0;
if (type->bounds ()->high.kind () == PROP_CONST)
high = type->bounds ()->high.const_val ();
else
high = 0;
break;
}

10
gdb/testsuite/ChangeLog
View file

@ -1,3 +1,13 @@
2021-04-22 Simon Marchi <simon.marchi@polymtl.ca>
PR gdb/27757
* gdb.python/flexible-array-member.c: New test.
* gdb.python/flexible-array-member.exp: New test.
* gdb.guile/scm-type.exp (test_range): Add test for flexible
array member.
* gdb.guile/scm-type.c (struct flex_member): New.
(main): Use it.
2021-04-22 Tom Tromey <tom@tromey.com>
* gdb.rust/modules.exp: Add checks for syntax errors.

12
gdb/testsuite/gdb.guile/scm-type.c
View file

@ -15,6 +15,8 @@
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 <stdlib.h>
struct s
{
int a;
@ -53,6 +55,12 @@ enum E
struct s vec_data_1 = {1, 1};
struct s vec_data_2 = {1, 2};
struct flex_member
{
int n;
int items[];
};
int
main ()
{
@ -72,6 +80,10 @@ main ()
st.b = 5;
e = v2;
struct flex_member *f = (struct flex_member *) malloc (100);
f->items[0] = 111;
f->items[1] = 222;
return 0; /* break to inspect struct and array. */
}

12
gdb/testsuite/gdb.guile/scm-type.exp
View file

@ -261,6 +261,18 @@ proc test_range {} {
"ERROR: .*: Wrong type argument in position 1 \\(expecting ranged type\\): .*" \
"check range for non ranged type"
}
with_test_prefix "on flexible array member" {
gdb_scm_test_silent_cmd "print f" "print value (f)"
gdb_scm_test_silent_cmd "guile (define f (history-ref 0))" \
"get value (f) from history"
gdb_test "guile (print (type-range (field-type (type-field (value-type (value-dereference f)) \"items\"))))" \
"= \\(0 0\\)"
gdb_test "guile (print (value-subscript (value-field (value-dereference f) \"items\") 0))" \
"= 111"
gdb_test "guile (print (value-subscript (value-field (value-dereference f) \"items\") 1))" \
"= 222"
}
}
}

70
gdb/testsuite/gdb.python/flexible-array-member.c Normal file
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@ -0,0 +1,70 @@
/* This testcase is part of GDB, the GNU debugger.
Copyright 2020-2021 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/>. */
#include <stdlib.h>
struct no_size
{
int n;
int items[];
};
struct zero_size
{
int n;
int items[0];
};
struct zero_size_only
{
int items[0];
};
struct no_size *ns;
struct zero_size *zs;
struct zero_size_only *zso;
static void
break_here (void)
{
}
int
main (void)
{
ns = (struct no_size *) malloc (sizeof (*ns) + 3 * sizeof (int));
zs = (struct zero_size *) malloc (sizeof (*zs) + 3 * sizeof (int));
zso = (struct zero_size_only *) malloc (sizeof (*zso) + 3 * sizeof (int));
ns->n = 3;
ns->items[0] = 101;
ns->items[1] = 102;
ns->items[2] = 103;
zs->n = 3;
zs->items[0] = 201;
zs->items[1] = 202;
zs->items[2] = 203;
zso->items[0] = 301;
zso->items[1] = 302;
zso->items[2] = 303;
break_here ();
return 0;
}

81
gdb/testsuite/gdb.python/flexible-array-member.exp Normal file
View file

@ -0,0 +1,81 @@
# Copyright 2020-2021 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/>.
# Test getting the range of flexible array members in Python.
standard_testfile
if { [prepare_for_testing "failed to prepare" \
${testfile} ${srcfile}] } {
return
}
if { ![runto break_here] } {
untested "could not run to break_here"
return
}
# The various cases are:
#
# - ns: flexible array member with no size
# - zs: flexible array member with size 0 (GNU C extension that predates the
# standardization of the feature, but widely supported)
# - zso: zero-size only, a corner case where the array is the sole member of
# the structure
gdb_test "python ns = gdb.parse_and_eval('ns').dereference()"
gdb_test "python zs = gdb.parse_and_eval('zs').dereference()"
gdb_test "python zso = gdb.parse_and_eval('zso').dereference()"
# Print the whole structure.
gdb_test "python print(ns)" "{n = 3, items = $hex}"
gdb_test "python print(zs)" "{n = 3, items = $hex}"
gdb_test "python print(zso)" "{items = $hex}"
# Print all items.
gdb_test "python print(ns\['items'\])" "$hex"
gdb_test "python print(ns\['items'\]\[0\])" "101"
gdb_test "python print(ns\['items'\]\[1\])" "102"
gdb_test "python print(ns\['items'\]\[2\])" "103"
gdb_test "python print(zs\['items'\])" "$hex"
gdb_test "python print(zs\['items'\]\[0\])" "201"
gdb_test "python print(zs\['items'\]\[1\])" "202"
gdb_test "python print(zs\['items'\]\[2\])" "203"
gdb_test "python print(zso\['items'\])" "$hex"
gdb_test "python print(zso\['items'\]\[0\])" "301"
gdb_test "python print(zso\['items'\]\[1\])" "302"
gdb_test "python print(zso\['items'\]\[2\])" "303"
# Check taking the address of array elements (how PR 28675 was originally
# reported).
gdb_test "python print(ns\['items'\] == ns\['items'\]\[0\].address)" "True"
gdb_test "python print(ns\['items'\]\[0\].address + 1 == ns\['items'\]\[1\].address)" "True"
gdb_test "python print(zs\['items'\] == zs\['items'\]\[0\].address)" "True"
gdb_test "python print(zs\['items'\]\[0\].address + 1 == zs\['items'\]\[1\].address)" "True"
gdb_test "python print(zso\['items'\] == zso\['items'\]\[0\].address)" "True"
gdb_test "python print(zso\['items'\]\[0\].address + 1 == zso\['items'\]\[1\].address)" "True"
# Verify the range attribute. It looks a bit inconsistent that the high bound
# is sometimes 0, sometimes -1, but that's what GDB produces today, so that's
# what we test.
gdb_test "python print(ns\['items'\].type.range())" "\\(0, 0\\)"
gdb_test "python print(zs\['items'\].type.range())" "\\(0, -1\\)"
gdb_test "python print(zso\['items'\].type.range())" "\\(0, -1\\)"