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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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

19
gdb/ChangeLog
View File

@ -1,3 +1,22 @@
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.
2020-04-24 Tom Tromey <tromey@adacore.com>
* dwarf2/loc.c (dwarf2_locexpr_baton_eval): Add

6
gdb/ada-lang.c
View File

@ -752,7 +752,7 @@ min_of_type (struct type *t)
LONGEST
ada_discrete_type_high_bound (struct type *type)
{
type = resolve_dynamic_type (type, NULL, 0);
type = resolve_dynamic_type (type, {}, 0);
switch (TYPE_CODE (type))
{
case TYPE_CODE_RANGE:
@ -773,7 +773,7 @@ ada_discrete_type_high_bound (struct type *type)
LONGEST
ada_discrete_type_low_bound (struct type *type)
{
type = resolve_dynamic_type (type, NULL, 0);
type = resolve_dynamic_type (type, {}, 0);
switch (TYPE_CODE (type))
{
case TYPE_CODE_RANGE:
@ -2508,7 +2508,7 @@ ada_value_primitive_packed_val (struct value *obj, const gdb_byte *valaddr,
staging.data (), staging.size (),
is_big_endian, has_negatives (type),
is_scalar);
type = resolve_dynamic_type (type, staging.data (), 0);
type = resolve_dynamic_type (type, staging, 0);
if (TYPE_LENGTH (type) < (bit_size + HOST_CHAR_BIT - 1) / HOST_CHAR_BIT)
{
/* This happens when the length of the object is dynamic,

4
gdb/ada-valprint.c
View File

@ -1057,7 +1057,9 @@ ada_value_print_1 (struct value *val, struct ui_file *stream, int recurse,
const gdb_byte *valaddr = value_contents_for_printing (val);
CORE_ADDR address = value_address (val);
type = ada_check_typedef (resolve_dynamic_type (type, valaddr, address));
gdb::array_view<const gdb_byte> view
= gdb::make_array_view (valaddr, TYPE_LENGTH (type));
type = ada_check_typedef (resolve_dynamic_type (type, view, address));
if (type != saved_type)
{
val = value_copy (val);

73
gdb/dwarf2/loc.c
View File

@ -2384,18 +2384,56 @@ dwarf2_evaluate_loc_desc (struct type *type, struct frame_info *frame,
NULL, 0);
}
/* Evaluates a dwarf expression and stores the result in VAL, expecting
that the dwarf expression only produces a single CORE_ADDR. FRAME is the
frame in which the expression is evaluated. ADDR is a context (location of
a variable) and might be needed to evaluate the location expression.
PUSH_INITIAL_VALUE is true if ADDR should be pushed on the stack
before evaluating the expression; this is required by certain
forms of DWARF expression. Returns 1 on success, 0 otherwise. */
/* A specialization of dwarf_evaluate_loc_desc that is used by
dwarf2_locexpr_baton_eval. This subclass exists to handle the case
where a caller of dwarf2_locexpr_baton_eval passes in some data,
but with the address being 0. In this situation, we arrange for
memory reads to come from the passed-in buffer. */
struct evaluate_for_locexpr_baton : public dwarf_evaluate_loc_desc
{
/* The data that was passed in. */
gdb::array_view<const gdb_byte> data_view;
CORE_ADDR get_object_address () override
{
if (data_view.data () == nullptr && obj_address == 0)
error (_("Location address is not set."));
return obj_address;
}
void read_mem (gdb_byte *buf, CORE_ADDR addr, size_t len) override
{
if (len == 0)
return;
/* Prefer the passed-in memory, if it exists. */
CORE_ADDR offset = addr - obj_address;
if (offset < data_view.size () && offset + len <= data_view.size ())
{
memcpy (buf, data_view.data (), len);
return;
}
read_memory (addr, buf, len);
}
};
/* Evaluates a dwarf expression and stores the result in VAL,
expecting that the dwarf expression only produces a single
CORE_ADDR. FRAME is the frame in which the expression is
evaluated. ADDR_STACK is a context (location of a variable) and
might be needed to evaluate the location expression.
PUSH_INITIAL_VALUE is true if the address (either from ADDR_STACK,
or the default of 0) should be pushed on the DWARF expression
evaluation stack before evaluating the expression; this is required
by certain forms of DWARF expression. Returns 1 on success, 0
otherwise. */
static int
dwarf2_locexpr_baton_eval (const struct dwarf2_locexpr_baton *dlbaton,
struct frame_info *frame,
CORE_ADDR addr,
const struct property_addr_info *addr_stack,
CORE_ADDR *valp,
bool push_initial_value)
{
@ -2404,11 +2442,17 @@ dwarf2_locexpr_baton_eval (const struct dwarf2_locexpr_baton *dlbaton,
if (dlbaton == NULL || dlbaton->size == 0)
return 0;
dwarf_evaluate_loc_desc ctx;
evaluate_for_locexpr_baton ctx;
ctx.frame = frame;
ctx.per_cu = dlbaton->per_cu;
ctx.obj_address = addr;
if (addr_stack == nullptr)
ctx.obj_address = 0;
else
{
ctx.obj_address = addr_stack->addr;
ctx.data_view = addr_stack->valaddr;
}
objfile = dlbaton->per_cu->objfile ();
@ -2418,7 +2462,7 @@ dwarf2_locexpr_baton_eval (const struct dwarf2_locexpr_baton *dlbaton,
ctx.offset = dlbaton->per_cu->text_offset ();
if (push_initial_value)
ctx.push_address (addr, false);
ctx.push_address (ctx.obj_address, false);
try
{
@ -2485,8 +2529,7 @@ dwarf2_evaluate_property (const struct dynamic_prop *prop,
= (const struct dwarf2_property_baton *) prop->data.baton;
gdb_assert (baton->property_type != NULL);
if (dwarf2_locexpr_baton_eval (&baton->locexpr, frame,
addr_stack ? addr_stack->addr : 0,
if (dwarf2_locexpr_baton_eval (&baton->locexpr, frame, addr_stack,
value, push_initial_value))
{
if (baton->locexpr.is_reference)
@ -2569,10 +2612,10 @@ dwarf2_evaluate_property (const struct dynamic_prop *prop,
}
if (pinfo == NULL)
error (_("cannot find reference address for offset property"));
if (pinfo->valaddr != NULL)
if (pinfo->valaddr.data () != NULL)
val = value_from_contents
(baton->offset_info.type,
pinfo->valaddr + baton->offset_info.offset);
pinfo->valaddr.data () + baton->offset_info.offset);
else
val = value_at (baton->offset_info.type,
pinfo->addr + baton->offset_info.offset);

2
gdb/dwarf2/loc.h
View File

@ -73,7 +73,7 @@ struct property_addr_info
struct type *type;
/* If not NULL, a buffer containing the object's value. */
const gdb_byte *valaddr;
gdb::array_view<const gdb_byte> valaddr;
/* The address of that object. */
CORE_ADDR addr;

6
gdb/findvar.c
View File

@ -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:

15
gdb/gdbtypes.c
View File

@ -2298,8 +2298,9 @@ compute_variant_fields_inner (struct type *type,
error (_("Cannot determine struct field location"
" (invalid location kind)"));
if (addr_stack->valaddr != NULL)
discr_value = unpack_field_as_long (type, addr_stack->valaddr, idx);
if (addr_stack->valaddr.data () != NULL)
discr_value = unpack_field_as_long (type, addr_stack->valaddr.data (),
idx);
else
{
CORE_ADDR addr = (addr_stack->addr
@ -2516,9 +2517,10 @@ resolve_dynamic_type_internal (struct type *type,
struct property_addr_info pinfo;
pinfo.type = check_typedef (TYPE_TARGET_TYPE (type));
pinfo.valaddr = NULL;
if (addr_stack->valaddr != NULL)
pinfo.addr = extract_typed_address (addr_stack->valaddr, type);
pinfo.valaddr = {};
if (addr_stack->valaddr.data () != NULL)
pinfo.addr = extract_typed_address (addr_stack->valaddr.data (),
type);
else
pinfo.addr = read_memory_typed_address (addr_stack->addr, type);
pinfo.next = addr_stack;
@ -2566,7 +2568,8 @@ resolve_dynamic_type_internal (struct type *type,
/* See gdbtypes.h */
struct type *
resolve_dynamic_type (struct type *type, const gdb_byte *valaddr,
resolve_dynamic_type (struct type *type,
gdb::array_view<const gdb_byte> valaddr,
CORE_ADDR addr)
{
struct property_addr_info pinfo

4
gdb/gdbtypes.h
View File

@ -2140,8 +2140,8 @@ extern void get_signed_type_minmax (struct type *, LONGEST *, LONGEST *);
ADDR specifies the location of the variable the type is bound to.
If TYPE has no dynamic properties return TYPE; otherwise a new type with
static properties is returned. */
extern struct type *resolve_dynamic_type (struct type *type,
const gdb_byte *valaddr,
extern struct type *resolve_dynamic_type
(struct type *type, gdb::array_view<const gdb_byte> valaddr,
CORE_ADDR addr);
/* * Predicate if the type has dynamic values, which are not resolved yet. */

2
gdb/valarith.c
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@ -220,7 +220,7 @@ value_subscripted_rvalue (struct value *array, LONGEST index, LONGEST lowerbound
CORE_ADDR address;
address = value_address (array) + elt_offs;
elt_type = resolve_dynamic_type (elt_type, NULL, address);
elt_type = resolve_dynamic_type (elt_type, {}, address);
}
return value_from_component (array, elt_type, elt_offs);

5
gdb/value.c
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@ -3477,7 +3477,10 @@ value_from_contents_and_address (struct type *type,
const gdb_byte *valaddr,
CORE_ADDR address)
{
struct type *resolved_type = resolve_dynamic_type (type, valaddr, address);
gdb::array_view<const gdb_byte> view;
if (valaddr != nullptr)
view = gdb::make_array_view (valaddr, TYPE_LENGTH (type));
struct type *resolved_type = resolve_dynamic_type (type, view, address);
struct type *resolved_type_no_typedef = check_typedef (resolved_type);
struct value *v;