gdb: make get_discrete_bounds check for non-constant range bounds

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

2 files changed, 20 insertions, 16 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 90168a3..162929f 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,10 @@
+2020-07-12  Simon Marchi  <simon.marchi@efficios.com>
+
+	* 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.
+
 2020-07-12  Simon Marchi  <simon.marchi@polymtl.ca>
 
 	* gdbtypes.h (TYPE_RANGE_DATA): Remove.  Update callers to use
diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index 957307e..4016556 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;