[PATCH 03/12] gdb: make get_discrete_bounds check for non-constant range bounds

Simon Marchi
2020-07-06T13:38:41Z

The next patch adds getters to the `dynamic_prop` structure. These
getters validate that the accessed data matches the property kind (for
example, to access the `const_val` field, the property must be of kind
`PROP_CONST`). It found one instance where we are accessing the
`const_val` data of a property that has the undefined kind.

This happens in function `get_discrete_bounds`, and is exposed by test
gdb.base/ptype.exp, amongst others. Without this patch, we would get:

$ ./gdb -q -nx --data-directory=data-directory testsuite/outputs/gdb.base/ptype/ptype -ex "ptype t_char_array"
Reading symbols from testsuite/outputs/gdb.base/ptype/ptype...
type = char [
/home/smarchi/src/binutils-gdb/gdb/gdbtypes.h:526: internal-error: LONGEST dynamic_prop::const_val() const: Assertion `m_kind == PROP_CONST' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.
Quit this debugging session? (y or n)

The `get_discrete_bounds` function returns the bounds of a type (not
only range types). For range types, it naturally uses the bound
properties that are intrinsic to the range type. It accesses these
properties using TYPE_LOW_BOUND and TYPE_HIGH_BOUND, which assume the
properties are defined and have constant values. This is sometimes not
the case, and the passed range type (as in the example above) has an
undefined high/upper bound.

Given its current interface (returning two LONGEST values for low and
high), `get_discrete_bounds` can't really work if the range type's
bounds are not both defined and both constant values.

This patch changes the function to return -1 (failure to get the bounds)
if any of the range type's bounds is not a constant value. It is
sufficient to fix the issue and it seems to keep the callers happy, at
least according to the testsuite.

A bit in `get_array_bounds` could be removed, since
`get_discrete_bounds` no longer returns 1 if a bound is undefined.

gdb/ChangeLog:

* gdbtypes.c (get_discrete_bounds): Return failure if
the range type's bounds are not both defined and constant
values.
(get_array_bounds): Update comment. Remove undefined bound check.

Change-Id: I047a3beee2c1e275f888cfc4778228339922bde9
---
gdb/gdbtypes.c | 29 +++++++++++++----------------
1 file changed, 13 insertions(+), 16 deletions(-)

diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index 957307ec6120..40165563b91a 100644
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -1028,8 +1028,11 @@ has_static_range (const struct range_bounds *bounds)

/* Set *LOWP and *HIGHP to the lower and upper bounds of discrete type
- TYPE. Return 1 if type is a range type, 0 if it is discrete (and
- bounds will fit in LONGEST), or -1 otherwise. */
+ TYPE.
+
+ Return 1 if type is a range type with two defined, constant bounds.
+ Else, return 0 if it is discrete (and bounds will fit in LONGEST).
+ Else, return -1. */

int
get_discrete_bounds (struct type *type, LONGEST *lowp, LONGEST *highp)
@@ -1038,8 +1041,15 @@ get_discrete_bounds (struct type *type, LONGEST *lowp, LONGEST *highp)
switch (type->code ())
{
case TYPE_CODE_RANGE:
+ /* This function currently only works for ranges with two defined,
+ constant bounds. */
+ if (type->bounds ()->low.kind () != PROP_CONST
+ || type->bounds ()->high.kind () != PROP_CONST)
+ return -1;
+
*lowp = TYPE_LOW_BOUND (type);
*highp = TYPE_HIGH_BOUND (type);
+
if (TYPE_TARGET_TYPE (type)->code () == TYPE_CODE_ENUM)
{
if (!discrete_position (TYPE_TARGET_TYPE (type), *lowp, lowp)
@@ -1107,14 +1117,7 @@ get_discrete_bounds (struct type *type, LONGEST *lowp, LONGEST *highp)
Save the high bound into HIGH_BOUND if not NULL.

Return 1 if the operation was successful. Return zero otherwise,
- in which case the values of LOW_BOUND and HIGH_BOUNDS are unmodified.
-
- We now simply use get_discrete_bounds call to get the values
- of the low and high bounds.
- get_discrete_bounds can return three values:
- 1, meaning that index is a range,
- 0, meaning that index is a discrete type,
- or -1 for failure. */
+ in which case the values of LOW_BOUND and HIGH_BOUNDS are unmodified. */

int
get_array_bounds (struct type *type, LONGEST *low_bound, LONGEST *high_bound)
@@ -1131,12 +1134,6 @@ get_array_bounds (struct type *type, LONGEST *low_bound, LONGEST *high_bound)
if (res == -1)
return 0;

- /* Check if the array bounds are undefined. */
- if (res == 1
- && ((low_bound && TYPE_ARRAY_LOWER_BOUND_IS_UNDEFINED (type))
- || (high_bound && TYPE_ARRAY_UPPER_BOUND_IS_UNDEFINED (type))))
- return 0;
-
if (low_bound)
*low_bound = low;

--
2.27.0