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Avoid crash from coerce_unspec_val_to_type

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With a certain Ada program, ada-lang.c:coerce_unspec_val_to_type can
cause a crash.  This function may copy a value, and in the particular
case in the crash, the new value's type is smaller than the original
type.  This causes coerce_unspec_val_to_type to create a lazy value --
but the original value is also not_lval, so later, when the value is
un-lazied, gdb asserts.

As with the previous patch, we believe there is a compiler bug here,
but it is difficult to reproduce, so we're not completely certain.

In the particular case we saw, the original value has record type, and
the record holds some variable-length arrays.  This leads to the
type's length being 0.  At the same time, the value is optimized out.

This patch changes coerce_unspec_val_to_type to handle an
optimized-out value correctly.

It also slightly restructures this code to avoid a crash should a
not_lval value wind up here.  This is a purely defensive change.

This change also made it clear that value_contents_copy_raw can now be
made static, so that is also done.

gdb/ChangeLog
2021-02-09  Tom Tromey  <tromey@adacore.com>

	* ada-lang.c (coerce_unspec_val_to_type): Avoid making lazy
	not_lval value.
	* value.c (value_contents_copy_raw): Now static.
	* value.h (value_contents_copy_raw): Don't declare.
This commit is contained in:
Tom Tromey 2021-02-09 12:15:39 -07:00
parent a4f0544b1b
commit f73e424f7b
4 changed files with 15 additions and 7 deletions
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7
gdb/ChangeLog
View File

@ -1,3 +1,10 @@
2021-02-09 Tom Tromey <tromey@adacore.com>
* ada-lang.c (coerce_unspec_val_to_type): Avoid making lazy
not_lval value.
* value.c (value_contents_copy_raw): Now static.
* value.h (value_contents_copy_raw): Don't declare.
2021-02-09 Tom Tromey <tromey@adacore.com>
* gdbtypes.c (resolve_dynamic_struct): Handle structure with no

10
gdb/ada-lang.c
View File

@ -601,13 +601,17 @@ coerce_unspec_val_to_type (struct value *val, struct type *type)
trying to allocate some memory for it. */
ada_ensure_varsize_limit (type);
if (value_lazy (val)
|| TYPE_LENGTH (type) > TYPE_LENGTH (value_type (val)))
if (value_optimized_out (val))
result = allocate_optimized_out_value (type);
else if (value_lazy (val)
/* Be careful not to make a lazy not_lval value. */
|| (VALUE_LVAL (val) != not_lval
&& TYPE_LENGTH (type) > TYPE_LENGTH (value_type (val))))
result = allocate_value_lazy (type);
else
{
result = allocate_value (type);
value_contents_copy_raw (result, 0, val, 0, TYPE_LENGTH (type));
value_contents_copy (result, 0, val, 0, TYPE_LENGTH (type));
}
set_value_component_location (result, val);
set_value_bitsize (result, value_bitsize (val));

2
gdb/value.c
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@ -1304,7 +1304,7 @@ value_ranges_copy_adjusted (struct value *dst, int dst_bit_offset,
It is assumed the contents of DST in the [DST_OFFSET,
DST_OFFSET+LENGTH) range are wholly available. */
void
static void
value_contents_copy_raw (struct value *dst, LONGEST dst_offset,
struct value *src, LONGEST src_offset, LONGEST length)
{

3
gdb/value.h
View File

@ -739,9 +739,6 @@ extern struct value *allocate_value_lazy (struct type *type);
extern void value_contents_copy (struct value *dst, LONGEST dst_offset,
struct value *src, LONGEST src_offset,
LONGEST length);
extern void value_contents_copy_raw (struct value *dst, LONGEST dst_offset,
struct value *src, LONGEST src_offset,
LONGEST length);
extern struct value *allocate_repeat_value (struct type *type, int count);