From e5ca03b41d2c94919d5cb59d8d7adad98c29d156 Mon Sep 17 00:00:00 2001 From: Pedro Alves Date: Tue, 9 Aug 2016 12:04:48 +0100 Subject: [PATCH] Fix PR gdb/20295: GDB segfaults printing bitfield member of optimized out value 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 , 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 * 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 * gdb.dwarf2/bitfield-parent-optimized-out.exp: New file. --- gdb/ChangeLog | 5 ++ gdb/testsuite/ChangeLog | 4 + .../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 diff --git a/gdb/ChangeLog b/gdb/ChangeLog index e5e6f2d4ce..dd874209e7 100644 --- a/gdb/ChangeLog +++ b/gdb/ChangeLog @@ -1,3 +1,8 @@ +2016-08-09 Pedro Alves + + * value.c (unpack_value_bitfield): Skip unpacking if the parent + has no contents buffer to begin with. + 2016-08-08 Pedro Alves * features/i386/amd64-avx-mpx-linux.c: Regenerate. diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog index 9f336df109..4b700591bf 100644 --- a/gdb/testsuite/ChangeLog +++ b/gdb/testsuite/ChangeLog @@ -1,3 +1,7 @@ +2016-08-09 Pedro Alves + + * gdb.dwarf2/bitfield-parent-optimized-out.exp: New file. + 2016-08-03 Tom Tromey PR python/18565: diff --git a/gdb/testsuite/gdb.dwarf2/bitfield-parent-optimized-out.exp b/gdb/testsuite/gdb.dwarf2/bitfield-parent-optimized-out.exp new file mode 100644 index 0000000000..27d80448db --- /dev/null +++ b/gdb/testsuite/gdb.dwarf2/bitfield-parent-optimized-out.exp @@ -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 . + +# 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" " = " +gdb_test "p var.bitfield" " = " +gdb_test "p var.intfield" " = " diff --git a/gdb/value.c b/gdb/value.c index cd59f43f01..d6eab24e62 100644 --- a/gdb/value.c +++ b/gdb/value.c @@ -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. */