gdb/dwarf: fix UBsan crash in read_subrange_type

When running gdb.ada/arrayptr.exp (and others) on Ubuntu 22.04, with the
`gnat-11` package installed (not `gnat`), with UBSan activated, I get:

    (gdb) break foo.adb:40
    /home/smarchi/src/binutils-gdb/gdb/dwarf2/read.c:17689:20: runtime error: shift exponent 127 is too large for 64-bit type 'long unsigned int'

The problematic DIEs are:

    0x00001460:       DW_TAG_subrange_type
                        DW_AT_lower_bound [DW_FORM_data1]   (0x00)
                        DW_AT_upper_bound [DW_FORM_data16]  (ffffffffffffffff3f00000000000000)
                        DW_AT_name [DW_FORM_strp]   ("foo__packed_array___XP7___XDLU_0__1180591620717411303423")
                        DW_AT_type [DW_FORM_ref4]   (0x0000153f "long_long_long_unsigned")
                        DW_AT_GNAT_descriptive_type [DW_FORM_ref4]  (0x0000147e)
                        DW_AT_artificial [DW_FORM_flag_present]     (true)

    0x0000153f:   DW_TAG_base_type
                    DW_AT_byte_size [DW_FORM_data1] (0x10)
                    DW_AT_encoding [DW_FORM_data1]  (DW_ATE_unsigned)
                    DW_AT_name [DW_FORM_strp]       ("long_long_long_unsigned")
                    DW_AT_artificial [DW_FORM_flag_present] (true)

When processed by this code:

    negative_mask =
      -((ULONGEST) 1 << (base_type->length () * TARGET_CHAR_BIT - 1));
    if (low.kind () == PROP_CONST
        && !base_type->is_unsigned () && (low.const_val () & negative_mask))
      low.set_const_val (low.const_val () | negative_mask);

When the base type's length (16 bytes in this case) is larger than a
ULONGEST (typically 8 bytes), the bit shift is too large.

My obvious fix is just to skip the fixup for base types larger than a
ULONGEST (8 bytes).  I don't think we really handle constant attribute
values larger than 8 bytes anyway, so this is part of a much larger
problem.

Add a test that replicates this situation, but uses bounds that fit in a
signed 64 bit, so we get a sensible result.

Change-Id: I8d0a24f3edd83b44e0761a0ce38922d3e2e112fb
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29386

0 files changed, 0 insertions, 0 deletions