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Forward VALUE_LVAL when avoiding side effects for STRUCTOP_STRUCT

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Assume foo_array is a pointer to a C structure. GDB must evaluate the
following expression properly, but it does not currently:

    (gdb) print 1 && &foo_array[1].a
    Attempt to take address of value not located in memory.

The problem is that in EVAL_AVOID_SIDE_EFFECTS mode,
eval.c:evaluate_subexp_standard always returns a not_lval value as the
result for a STRUCTOP_STRUCT operation. As a consequence, the rest of
the code believes that one cannot take the address of the returned
value.

This patch fixes STRUCTOP_STRUCT handling so that the VALUE_LVAL
attribute for the returned value is properly initialized.  After this
change, the above session becomes:

    (gdb) print 1 && &foo_array[1].a
    $1 = 1

gdb/ChangeLog:

	* eval.c (evaluate_subexp_standard) <STRUCTOP_STRUCT>: If
	EVAL_AVOID_SIDE_EFFECTS mode, forward the VALUE_LVAL attribute
	to the returned value.

gdb/testsuite/ChangeLog:

	* gdb.base/nested-addr.c: New file.
	* gdb.base/nested-addr.exp: New testcase.

Tested on x86_64-linux, no regression.
This commit is contained in:
Pierre-Marie de Rodat 2015-09-15 15:46:17 +02:00
parent 431ff0756a
commit 2520f728b7
5 changed files with 81 additions and 1 deletions
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6
gdb/ChangeLog
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@ -1,3 +1,9 @@
2015-10-12 Pierre-Marie de Rodat <derodat@adacore.com>
* eval.c (evaluate_subexp_standard) <STRUCTOP_STRUCT>: If
EVAL_AVOID_SIDE_EFFECTS mode, forward the VALUE_LVAL attribute
to the returned value.
2015-10-09 Joel Brobecker <brobecker@adacore.com>
* ada-lang.c (ada_unpack_from_contents): Add guard that unpacked

2
gdb/eval.c
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@ -1862,7 +1862,7 @@ evaluate_subexp_standard (struct type *expect_type,
arg3 = value_struct_elt (&arg1, NULL, &exp->elts[pc + 2].string,
NULL, "structure");
if (noside == EVAL_AVOID_SIDE_EFFECTS)
arg3 = value_zero (value_type (arg3), not_lval);
arg3 = value_zero (value_type (arg3), VALUE_LVAL (arg3));
return arg3;
case STRUCTOP_PTR:

5
gdb/testsuite/ChangeLog
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@ -1,3 +1,8 @@
2015-10-12 Pierre-Marie de Rodat <derodat@adacore.com>
* gdb.base/nested-addr.c: New file.
* gdb.base/nested-addr.exp: New testcase.
2015-10-09 Markus Metzger <markus.t.metzger@intel.com>
* gdb.btrace/vdso.c (main): Remove breakpoint markers.

35
gdb/testsuite/gdb.base/nested-addr.c Normal file
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@ -0,0 +1,35 @@
/* This testcase is part of GDB, the GNU debugger.
Copyright 2015 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>
typedef struct foo
{
int a;
int b;
} foo;
static foo *foo_array = NULL;
int
main (void)
{
foo_array = calloc (3, sizeof (*foo_array));
foo_array[1].a = 10;
foo_array[2].b = 20;
return 0; /* BREAK */
}

34
gdb/testsuite/gdb.base/nested-addr.exp Normal file
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@ -0,0 +1,34 @@
# Copyright 2015 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/>. */
standard_testfile
if {[prepare_for_testing "${testfile}.exp" "${testfile}" "${srcfile}"]} {
return -1
}
if ![runto_main] {
return -1
}
gdb_breakpoint [gdb_get_line_number "BREAK"]
gdb_continue_to_breakpoint "BREAK"
# Sanity checking:
gdb_test "print &foo_array\[1\].a" "= \\(int \\*\\) $hex.*"
# A bug in EVAL_AVOID_SIDE_EFFECTS mode used to yield the following error:
# Attempt to take address of value not located in memory.
gdb_test "print 1 && &foo_array\[1\].a" "= 1"