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Prefer existing data when evaluating DWARF expression

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When evaluating a DWARF expression, the dynamic type resolution code
will pass in a buffer of bytes via the property_addr_info.  However,
the DWARF expression evaluator will then proceed to read memory from
the inferior, even when the request could be filled from this buffer.

This, in turn, is a problem in some cases; and specifically when
trying to handle the Ada scenario of extracting a variable-length
value from a packed array.  Here, the ordinary DWARF expression cannot
be directly evaluated, because the data may appear at some arbitrary
bit offset.  So, it is unpacked into a staging area and then the
expression is evaluated -- using an address of 0.

This patch fixes the problem by arranging for the DWARF evaluator, in
this case, to prefer passed-in memory when possible.  The type of the
buffer in the property_addr_info is changed to an array_view so that
bounds checking can be done.

gdb/ChangeLog
2020-04-24  Tom Tromey  <tromey@adacore.com>

	* ada-lang.c (ada_discrete_type_high_bound, ada_discrete_type_low)
	(ada_value_primitive_packed_val): Update.
	* ada-valprint.c (ada_value_print_1): Update.
	* dwarf2/loc.c (evaluate_for_locexpr_baton): New struct.
	(dwarf2_locexpr_baton_eval): Take a property_addr_info rather than
	just an address.  Use evaluate_for_locexpr_baton.
	(dwarf2_evaluate_property): Update.
	* dwarf2/loc.h (struct property_addr_info) <valaddr>: Now an
	array_view.
	* findvar.c (default_read_var_value): Update.
	* gdbtypes.c (compute_variant_fields_inner)
	(resolve_dynamic_type_internal): Update.
	(resolve_dynamic_type): Change type of valaddr parameter.
	* gdbtypes.h (resolve_dynamic_type): Update.
	* valarith.c (value_subscripted_rvalue): Update.
	* value.c (value_from_contents_and_address): Update.
This commit is contained in:
Tom Tromey
2020-04-24 13:40:31 -06:00
parent 61122aa9ed
commit b249d2c2c0
10 changed files with 104 additions and 34 deletions
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6
gdb/findvar.c
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@@ -615,7 +615,7 @@ default_read_var_value (struct symbol *var, const struct block *var_block,
if (is_dynamic_type (type))
{
/* Value is a constant byte-sequence and needs no memory access. */
type = resolve_dynamic_type (type, NULL, /* Unused address. */ 0);
type = resolve_dynamic_type (type, {}, /* Unused address. */ 0);
}
/* Put the constant back in target format. */
v = allocate_value (type);
@@ -647,7 +647,7 @@ default_read_var_value (struct symbol *var, const struct block *var_block,
if (is_dynamic_type (type))
{
/* Value is a constant byte-sequence and needs no memory access. */
type = resolve_dynamic_type (type, NULL, /* Unused address. */ 0);
type = resolve_dynamic_type (type, {}, /* Unused address. */ 0);
}
v = allocate_value (type);
memcpy (value_contents_raw (v), SYMBOL_VALUE_BYTES (var),
@@ -788,7 +788,7 @@ default_read_var_value (struct symbol *var, const struct block *var_block,
case LOC_OPTIMIZED_OUT:
if (is_dynamic_type (type))
type = resolve_dynamic_type (type, NULL, /* Unused address. */ 0);
type = resolve_dynamic_type (type, {}, /* Unused address. */ 0);
return allocate_optimized_out_value (type);
default: