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[binutils-gdb] error/internal-error printing local variable during "bt full".
- From: Joel Brobecker <brobecke at sourceware dot org>
- To: gdb-cvs at sourceware dot org
- Date: 23 Nov 2015 18:03:28 -0000
- Subject: [binutils-gdb] error/internal-error printing local variable during "bt full".
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=16c3b12f199a7ec99a0b51bd83b66942547bba87
commit 16c3b12f199a7ec99a0b51bd83b66942547bba87
Author: Joel Brobecker <brobecker@adacore.com>
Date: Mon Nov 23 10:02:50 2015 -0800
error/internal-error printing local variable during "bt full".
One of our users reported an internal error using the "bt full"
command. In their situation, reproducing involved the following
scenario:
(gdb) frame 1
(gdb) bt full
#0 0xf7783430 in __kernel_vsyscall ()
No symbol table info available.
#1 0xf5550aeb in waitpid () at ../sysdeps/unix/syscall-template.S:81
No locals.
[...]
#6 0x0fe83139 in xxxx (arg=...)
[...some locals printed, and then...]
<S17b> =
[...]/dwarf2loc.c:364: internal-error: dwarf_expr_frame_base: Assertion
`framefunc != NULL' failed.
As shown above, the error happens while GDB is trying to print the value
of <S17b>, which is a local string internally generated by the compiler.
For that, it finds that the array lives in memory, and therefore tries
to create a struct value for it via:
case DWARF_VALUE_MEMORY:
{
CORE_ADDR address = dwarf_expr_fetch_address (ctx, 0);
[...]
retval = value_at_lazy (type, address + byte_offset);
Unfortunately for us, TYPE happens to be an array whose bounds
are dynamic. More precisely, the bounds of our arrays are described
in the debugging info as being...
<4><2c1985e>: Abbrev Number: 33 (DW_TAG_subrange_type)
<2c1985f> DW_AT_type : <0x2c1989c>
<2c19863> DW_AT_lower_bound : <0x2c19835>
<2c19867> DW_AT_upper_bound : <0x2c19841>
... which are references to a pair of local variables. For instance,
the lower bound is a reference to the following DIE
<3><2c19835>: Abbrev Number: 32 (DW_TAG_variable)
<2c19836> DW_AT_name : [...]
<2c1983a> DW_AT_type : <0x2c198b4>
<2c1983e> DW_AT_artificial : 1
<2c1983e> DW_AT_location : 2 byte block: 91 58 (DW_OP_fbreg: -40)
As a result of the above, value_at_lazy indirectly triggers
a resolution of TYPE (via value_from_contents_and_address),
which means a resolution of TYPE's bounds, and as seen in
the DW_AT_location attribute above for our bounds, computing
the bound's location requires the frame (its location expression
uses DW_OP_fbreg).
Unfortunately for us, value_at_lazy does not get passed a frame,
we've lost the relevant frame when we try to resolve the array's
bounds. Instead, resolve_dynamic_range gets calls dwarf2_evaluate_property
with NULL as the frame:
static struct type *
resolve_dynamic_range (struct type *dyn_range_type,
struct property_addr_info *addr_stack)
{
[...]
if (dwarf2_evaluate_property (prop, NULL, addr_stack, &value))
^^^^
... which then handles this by using the selected frame instead:
if (frame == NULL && has_stack_frames ())
frame = get_selected_frame (NULL);
In our case, the selected frame happens to be frame #1, which is
a frame where we have a minimal amount of debugging info, and in
particular, no debug info for the function itself. And because of that,
when we try to determine the frame's base...
static void
dwarf_expr_frame_base (void *baton, const gdb_byte **start,
size_t * length)
{
struct dwarf_expr_baton *debaton = (struct dwarf_expr_baton *) baton;
const struct block *bl = get_frame_block (debaton->frame, NULL);
[...]
framefunc = block_linkage_function (bl);
... framefunc ends up being NULL, which triggers the assert
in that same function:
gdb_assert (framefunc != NULL);
This patches avoids the issue by temporarily setting the selected_frame
before printing the locals of each frames.
This patch also adds a small testcase, which reproduces the same
issue, but with a slightly different outcome:
(gdb) bt full
#0 0x000000000040049a in opaque_routine ()
No symbol table info available.
#1 0x0000000000400532 in main () at wrong_frame_bt_full-main.c:20
my_table_size = 3
my_table = <error reading variable my_table (frame address is not available.)>
With this patch, the output becomes:
(gdb) bt full
[...]
my_table = {0, 1, 2}
gdb/ChangeLog:
* stack.c (print_frame_local_vars): Temporarily set the selected
frame to FRAME while printing the frame's local variables.
gdb/testsuite/ChangeLog:
* gdb.base/wrong_frame_bt_full-main.c: New file.
* gdb.base/wrong_frame_bt_full-opaque.c: New file.
* gdb.base/wrong_frame_bt_full.exp: New file.
Diff:
---
gdb/ChangeLog | 5 ++
gdb/stack.c | 25 ++++++++--
gdb/testsuite/ChangeLog | 6 +++
gdb/testsuite/gdb.base/wrong_frame_bt_full-main.c | 34 +++++++++++++
.../gdb.base/wrong_frame_bt_full-opaque.c | 22 +++++++++
gdb/testsuite/gdb.base/wrong_frame_bt_full.exp | 55 ++++++++++++++++++++++
6 files changed, 144 insertions(+), 3 deletions(-)
diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index ffcac03..d648e56 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,10 @@
2015-11-23 Joel Brobecker <brobecker@adacore.com>
+ * stack.c (print_frame_local_vars): Temporarily set the selected
+ frame to FRAME while printing the frame's local variables.
+
+2015-11-23 Joel Brobecker <brobecker@adacore.com>
+
* amd64-windows-tdep.c (amd64_windows_frame_decode_epilogue):
Increment PC in while loop skipping "pop reg" instructions.
diff --git a/gdb/stack.c b/gdb/stack.c
index b825bdf..163b72d 100644
--- a/gdb/stack.c
+++ b/gdb/stack.c
@@ -2082,6 +2082,7 @@ print_frame_local_vars (struct frame_info *frame, int num_tabs,
struct print_variable_and_value_data cb_data;
const struct block *block;
CORE_ADDR pc;
+ struct gdb_exception except = exception_none;
if (!get_frame_pc_if_available (frame, &pc))
{
@@ -2102,9 +2103,27 @@ print_frame_local_vars (struct frame_info *frame, int num_tabs,
cb_data.stream = stream;
cb_data.values_printed = 0;
- iterate_over_block_local_vars (block,
- do_print_variable_and_value,
- &cb_data);
+ /* Temporarily change the selected frame to the given FRAME.
+ This allows routines that rely on the selected frame instead
+ of being given a frame as parameter to use the correct frame. */
+ select_frame (frame);
+
+ TRY
+ {
+ iterate_over_block_local_vars (block,
+ do_print_variable_and_value,
+ &cb_data);
+ }
+ CATCH (ex, RETURN_MASK_ALL)
+ {
+ except = ex;
+ }
+ END_CATCH
+
+ /* Restore the selected frame, and then rethrow if there was a problem. */
+ select_frame (frame_find_by_id (cb_data.frame_id));
+ if (except.reason < 0)
+ throw_exception (except);
/* do_print_variable_and_value invalidates FRAME. */
frame = NULL;
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 6518f14..2c59ad8 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,5 +1,11 @@
2015-11-23 Joel Brobecker <brobecker@adacore.com>
+ * gdb.base/wrong_frame_bt_full-main.c: New file.
+ * gdb.base/wrong_frame_bt_full-opaque.c: New file.
+ * gdb.base/wrong_frame_bt_full.exp: New file.
+
+2015-11-23 Joel Brobecker <brobecker@adacore.com>
+
* testsuite/gdb.ada/var_rec_arr.exp: Add "ptype a1(1)" test.
2015-11-20 Jose E. Marchesi <jose.marchesi@oracle.com>
diff --git a/gdb/testsuite/gdb.base/wrong_frame_bt_full-main.c b/gdb/testsuite/gdb.base/wrong_frame_bt_full-main.c
new file mode 100644
index 0000000..73ab34c
--- /dev/null
+++ b/gdb/testsuite/gdb.base/wrong_frame_bt_full-main.c
@@ -0,0 +1,34 @@
+/* Copyright (C) 2015 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/>. */
+
+extern void opaque_routine (void);
+
+int dyn_arr_size = 4;
+
+int
+main (void)
+{
+ int i;
+ int my_table_size = dyn_arr_size - 1;
+ int my_table [my_table_size];
+
+ for (i = 0; i < my_table_size; i++)
+ my_table[i] = i;
+
+ opaque_routine ();
+ return 0;
+}
diff --git a/gdb/testsuite/gdb.base/wrong_frame_bt_full-opaque.c b/gdb/testsuite/gdb.base/wrong_frame_bt_full-opaque.c
new file mode 100644
index 0000000..19b8770
--- /dev/null
+++ b/gdb/testsuite/gdb.base/wrong_frame_bt_full-opaque.c
@@ -0,0 +1,22 @@
+/* Copyright (C) 2015 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/>. */
+
+void
+opaque_routine (void)
+{
+ /* Do nothing. */
+}
diff --git a/gdb/testsuite/gdb.base/wrong_frame_bt_full.exp b/gdb/testsuite/gdb.base/wrong_frame_bt_full.exp
new file mode 100644
index 0000000..863cc1b
--- /dev/null
+++ b/gdb/testsuite/gdb.base/wrong_frame_bt_full.exp
@@ -0,0 +1,55 @@
+# Copyright (C) 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/>.
+
+# Build wrong_frame_bt_full-main using two C files:
+# - wrong_frame_bt_full-opaque.c, which needs to be built without
+# debugging info;
+# - wrong_frame_bt_full-main.c, which needs to be built with
+# debugging info.
+# This is why we use gdb_compile instead of relying on he usual call
+# to prepare_for_testing.
+
+set main_testfile wrong_frame_bt_full-main
+set opaque_testfile wrong_frame_bt_full-opaque
+
+if {[gdb_compile "${srcdir}/${subdir}/$opaque_testfile.c" \
+ $opaque_testfile.o \
+ object {}] != ""} {
+ untested "failed to compile $opaque_testfile.c"
+ return -1
+}
+
+if {[gdb_compile \
+ [list ${srcdir}/${subdir}/$main_testfile.c $opaque_testfile.o] \
+ [standard_output_file ${main_testfile}] \
+ executable {debug}] != ""} {
+ untested "failed to build $main_testfile"
+ return -1
+}
+
+clean_restart ${main_testfile}
+
+if ![runto opaque_routine] {
+ untested "could not run to opaque_routine"
+ return -1
+}
+
+# Make sure that "bt full" command is capable of displaying MY_TABLE
+# correctly when frame #0 (the frame which does not have any debugging
+# info) is the selected frame.
+
+gdb_test "bt full" \
+ ".*\[\r\n\]+ *my_table = \\{0, 1, 2\\}\[\r\n\]+.*"
+