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Fix PR gdb/20295: GDB segfaults printing bitfield member of optimized out value

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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.
This commit is contained in:
Pedro Alves 2016-08-09 12:04:48 +01:00
parent 02183cb7d3
commit e5ca03b41d
4 changed files with 111 additions and 8 deletions
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23
gdb/value.c
View file

@ -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. */