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gdb/dwarf: fix UBsan crash in read_subrange_type

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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
This commit is contained in:
Simon Marchi 2023-01-20 11:51:54 -05:00
parent 173628ae68
commit b70bff5ea5
2 changed files with 41 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

29
gdb/dwarf2/read.c
View File

@ -17588,7 +17588,6 @@ read_subrange_type (struct die_info *die, struct dwarf2_cu *cu)
int low_default_is_valid;
int high_bound_is_count = 0;
const char *name;
ULONGEST negative_mask;
orig_base_type = read_subrange_index_type (die, cu);
@ -17684,15 +17683,25 @@ read_subrange_type (struct die_info *die, struct dwarf2_cu *cu)
with GCC, for instance, where the ambiguous DW_FORM_dataN form
is used instead. To work around that ambiguity, we treat
the bounds as signed, and thus sign-extend their values, when
the base type is signed. */
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);
if (high.kind () == PROP_CONST
&& !base_type->is_unsigned () && (high.const_val () & negative_mask))
high.set_const_val (high.const_val () | negative_mask);
the base type is signed.
Skip it if the base type's length is larger than ULONGEST, to avoid
the undefined behavior of a too large left shift. We don't really handle
constants larger than 8 bytes anyway, at the moment. */
if (base_type->length () <= sizeof (ULONGEST))
{
ULONGEST 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);
if (high.kind () == PROP_CONST
&& !base_type->is_unsigned () && (high.const_val () & negative_mask))
high.set_const_val (high.const_val () | negative_mask);
}
/* Check for bit and byte strides. */
struct dynamic_prop byte_stride_prop;

22
gdb/testsuite/gdb.dwarf2/subrange.exp
View File

@ -77,6 +77,26 @@ Dwarf::assemble $asm_file {
{name subrange_with_buggy_negative_bounds_variable}
{type :$subrange_with_buggy_negative_bounds_label}
}
# This subrange's base type is 16-bytes long (although the bounds fit in
# signed 64-bit). This is to test the fix for PR 29386.
declare_labels a_16_byte_integer_label a_16_byte_subrange_label
a_16_byte_integer_label: base_type {
{byte_size 16 udata}
{encoding @DW_ATE_signed}
}
a_16_byte_subrange_label: subrange_type {
{lower_bound -9223372036854775808 DW_FORM_sdata}
{upper_bound 9223372036854775807 DW_FORM_sdata}
{type :$a_16_byte_integer_label}
}
DW_TAG_variable {
{name a_16_byte_subrange_variable}
{type :$a_16_byte_subrange_label}
}
}
}
}
@ -92,3 +112,5 @@ gdb_test "ptype TByteArray" \
"type = array \\\[0\\.\\.191\\\] of byte"
gdb_test "ptype subrange_with_buggy_negative_bounds_variable" \
"type = -16\\.\\.-12"
gdb_test "ptype a_16_byte_subrange_variable" \
"type = -9223372036854775808\\.\\.9223372036854775807"