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.
