[pushed,master+7.12] Fix PR gdb/20295: GDB segfaults printing bitfield member of optimized out value
Commit Message
[I think this is a pretty obvious and safe fix, so I went ahead and
pushed it to both master and 7.12.]
With something like:
struct A { int bitfield:4; } var;
If 'var' ends up wholly-optimized out, printing 'var.bitfield' crashes
gdb here:
(top-gdb) bt
#0 0x000000000058b89f in extract_unsigned_integer (addr=0x2 <error: Cannot access memory at address 0x2>, len=2, byte_order=BFD_ENDIAN_LITTLE)
at /home/pedro/gdb/mygit/src/gdb/findvar.c:109
#1 0x00000000005a187a in unpack_bits_as_long (field_type=0x16cff70, valaddr=0x0, bitpos=16, bitsize=12) at /home/pedro/gdb/mygit/src/gdb/value.c:3347
#2 0x00000000005a1b9d in unpack_value_bitfield (dest_val=0x1b5d9d0, bitpos=16, bitsize=12, valaddr=0x0, embedded_offset=0, val=0x1b5d8d0)
at /home/pedro/gdb/mygit/src/gdb/value.c:3441
#3 0x00000000005a2a5f in value_fetch_lazy (val=0x1b5d9d0) at /home/pedro/gdb/mygit/src/gdb/value.c:3958
#4 0x00000000005a10a7 in value_primitive_field (arg1=0x1b5d8d0, offset=0, fieldno=0, arg_type=0x16d04c0) at /home/pedro/gdb/mygit/src/gdb/value.c:3161
#5 0x00000000005b01e5 in do_search_struct_field (name=0x1727c60 "bitfield", arg1=0x1b5d8d0, offset=0, type=0x16d04c0, looking_for_baseclass=0, result_ptr=0x7fffffffcaf8,
[...]
unpack_value_bitfield is already optimized-out/unavailable -aware:
(...) VALADDR points to the contents of VAL. If the VAL's contents
required to extract the bitfield from are unavailable/optimized
out, DEST_VAL is correspondingly marked unavailable/optimized out.
however, it is not considering the case of the value having no
contents buffer at all, as can happen through
allocate_optimized_out_value.
gdb/ChangeLog:
2016-08-09 Pedro Alves <palves@redhat.com>
* value.c (unpack_value_bitfield): Skip unpacking if the parent
has no contents buffer to begin with.
gdb/testsuite/ChangeLog:
2016-08-09 Pedro Alves <palves@redhat.com>
* gdb.dwarf2/bitfield-parent-optimized-out.exp: New file.
---
gdb/ChangeLog | 5 ++
gdb/testsuite/ChangeLog | 4 +
.../gdb.dwarf2/bitfield-parent-optimized-out.exp | 87 ++++++++++++++++++++++
gdb/value.c | 23 ++++--
4 files changed, 111 insertions(+), 8 deletions(-)
create mode 100644 gdb/testsuite/gdb.dwarf2/bitfield-parent-optimized-out.exp
@@ -1,3 +1,8 @@
+2016-08-09 Pedro Alves <palves@redhat.com>
+
+ * value.c (unpack_value_bitfield): Skip unpacking if the parent
+ has no contents buffer to begin with.
+
2016-08-08 Pedro Alves <palves@redhat.com>
* features/i386/amd64-avx-mpx-linux.c: Regenerate.
@@ -1,3 +1,7 @@
+2016-08-09 Pedro Alves <palves@redhat.com>
+
+ * gdb.dwarf2/bitfield-parent-optimized-out.exp: New file.
+
2016-08-03 Tom Tromey <tom@tromey.com>
PR python/18565:
new file mode 100644
@@ -0,0 +1,87 @@
+# Copyright 2016 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 printing a bitfield of an optimized-out variable. Regression
+# test for PR gdb/20295.
+
+load_lib dwarf.exp
+
+# This test can only be run on targets which support DWARF-2 and use gas.
+if {![dwarf2_support]} {
+ return 0
+}
+
+standard_testfile main.c .S
+set executable ${testfile}
+
+# Make some DWARF for the test.
+set asm_file [standard_output_file $srcfile2]
+Dwarf::assemble $asm_file {
+ global srcdir subdir srcfile
+
+ cu { version 3 addr_size 4 } {
+ compile_unit {} {
+ declare_labels struct_label var_label int_label
+
+ int_label: base_type {
+ {byte_size 4 sdata}
+ {encoding @DW_ATE_signed}
+ {name int}
+ }
+
+ struct_label: structure_type {
+ {name S}
+ {byte_size 4 DW_FORM_sdata}
+ } {
+ member {
+ {name bitfield}
+ {type :$int_label}
+ {bit_size 12 DW_FORM_sdata}
+ {bit_offset 20 DW_FORM_sdata}
+ {data_member_location 2 DW_FORM_sdata}
+ }
+ member {
+ {name intfield}
+ {type :$int_label}
+ {data_member_location 2 DW_FORM_sdata}
+ }
+ }
+
+ subprogram {
+ {MACRO_AT_func { main ${srcdir}/${subdir}/${srcfile} }}
+ {type :$int_label}
+ {external 1 flag}
+ } {
+ var_label: DW_TAG_variable {
+ {name var}
+ {location {} DW_FORM_block1}
+ {type :$struct_label}
+ }
+ }
+ }
+ }
+}
+
+if [prepare_for_testing ${testfile}.exp $executable "${asm_file} ${srcfile}" {}] {
+ return -1
+}
+
+if ![runto_main] {
+ return -1
+}
+
+gdb_test "p var" " = <optimized out>"
+gdb_test "p var.bitfield" " = <optimized out>"
+gdb_test "p var.intfield" " = <optimized out>"
@@ -3430,17 +3430,24 @@ unpack_value_bitfield (struct value *dest_val,
enum bfd_endian byte_order;
int src_bit_offset;
int dst_bit_offset;
- LONGEST num;
struct type *field_type = value_type (dest_val);
- /* First, unpack and sign extend the bitfield as if it was wholly
- available. Invalid/unavailable bits are read as zero, but that's
- OK, as they'll end up marked below. */
byte_order = gdbarch_byte_order (get_type_arch (field_type));
- num = unpack_bits_as_long (field_type, valaddr + embedded_offset,
- bitpos, bitsize);
- store_signed_integer (value_contents_raw (dest_val),
- TYPE_LENGTH (field_type), byte_order, num);
+
+ /* First, unpack and sign extend the bitfield as if it was wholly
+ valid. Optimized out/unavailable bits are read as zero, but
+ that's OK, as they'll end up marked below. If the VAL is
+ wholly-invalid we may have skipped allocating its contents,
+ though. See allocate_optimized_out_value. */
+ if (valaddr != NULL)
+ {
+ LONGEST num;
+
+ num = unpack_bits_as_long (field_type, valaddr + embedded_offset,
+ bitpos, bitsize);
+ store_signed_integer (value_contents_raw (dest_val),
+ TYPE_LENGTH (field_type), byte_order, num);
+ }
/* Now copy the optimized out / unavailability ranges to the right
bits. */