In C++, call-by-value arguments that cannot be trivially copied are
implicitly passed by reference. When making an infcall, GDB needs to
find out if an argument is pass-by-reference or not, so that the
correct semantics can be followed. This patch enriches the
information computed by the language ops for pass-by-reference
arguments. Instead of a plain binary result, the computed information
now includes whether the argument is
- copy constructible
- destructible
- trivially copyable
- trivially copy constructible
- trivially destructible
This information is stored in a struct named 'language_pass_by_ref_info'.
This patch paves the way for GDB's infcall mechanism to call the copy
ctor and the destructor of a pass-by-ref argument appropriately.
gdb/ChangeLog:
2019-12-20 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
* language.h (struct language_pass_by_ref_info): New struct.
(struct language_defn)<la_pass_by_reference>: Change the signature
to return a language_pass_by_ref_info instead of an int.
(language_pass_by_reference): Ditto.
(default_pass_by_reference): Ditto.
Adjust the users listed below.
* arch-utils.c (default_return_in_first_hidden_param_p):
Update.
* cp-abi.c (cp_pass_by_reference): Update.
* cp-abi.h (cp_pass_by_reference): Update declaration.
(struct cp_abi_ops)<pass_by_reference>: Update.
* gnu-v3-abi.c (gnuv3_pass_by_reference): Update.
* infcall.c (call_function_by_hand_dummy): Update.
* language.c (language_pass_by_reference): Update.
(default_pass_by_reference): Update.
* tic6x-tdep.c (tic6x_return_value): Update.
Change-Id: Ib1c1f87f2490a5737c469f7b7185ddc7f6a164cb
+2019-12-20 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
+
+ * language.h (struct language_pass_by_ref_info): New struct.
+ (struct language_defn)<la_pass_by_reference>: Change the signature
+ to return a language_pass_by_ref_info instead of an int.
+ (language_pass_by_reference): Ditto.
+ (default_pass_by_reference): Ditto.
+ Adjust the users listed below.
+ * arch-utils.c (default_return_in_first_hidden_param_p):
+ Update.
+ * cp-abi.c (cp_pass_by_reference): Update.
+ * cp-abi.h (cp_pass_by_reference): Update declaration.
+ (struct cp_abi_ops)<pass_by_reference>: Update.
+ * gnu-v3-abi.c (gnuv3_pass_by_reference): Update.
+ * infcall.c (call_function_by_hand_dummy): Update.
+ * language.c (language_pass_by_reference): Update.
+ (default_pass_by_reference): Update.
+ * tic6x-tdep.c (tic6x_return_value): Update.
+
2019-12-20 Tankut Baris Aktemur <tankut.baris.aktemur@intel.com>
* dwarf2read.c (dwarf2_add_member_fn): Read the DW_AT_defaulted
/* Usually, the return value's address is stored the in the "first hidden"
parameter if the return value should be passed by reference, as
specified in ABI. */
- return language_pass_by_reference (type);
+ return !(language_pass_by_reference (type).trivially_copyable);
}
int default_insn_is_call (struct gdbarch *gdbarch, CORE_ADDR addr)
return (*current_cp_abi.get_typename_from_type_info) (value);
}
-int
+/* See cp-abi.h. */
+
+struct language_pass_by_ref_info
cp_pass_by_reference (struct type *type)
{
if ((current_cp_abi.pass_by_reference) == NULL)
- return 0;
+ return default_pass_by_reference (type);
return (*current_cp_abi.pass_by_reference) (type);
}
CORE_ADDR cplus_skip_trampoline (struct frame_info *frame,
CORE_ADDR stop_pc);
-/* Return non-zero if an argument of type TYPE should be passed by
- reference instead of value. */
-extern int cp_pass_by_reference (struct type *type);
+/* Return a struct that provides pass-by-reference information
+ about the given TYPE. */
+
+extern struct language_pass_by_ref_info cp_pass_by_reference
+ (struct type *type);
struct cp_abi_ops
{
struct type *(*get_type_from_type_info) (struct value *value);
std::string (*get_typename_from_type_info) (struct value *value);
CORE_ADDR (*skip_trampoline) (struct frame_info *, CORE_ADDR);
- int (*pass_by_reference) (struct type *type);
+ struct language_pass_by_ref_info (*pass_by_reference) (struct type *type);
};
return real_stop_pc;
}
-/* Return nonzero if a type should be passed by reference.
+/* Return pass-by-reference information for the given TYPE.
The rule in the v3 ABI document comes from section 3.1.1. If the
type has a non-trivial copy constructor or destructor, then the
We don't do anything with the constructors or destructors,
but we have to get the argument passing right anyway. */
-static int
+
+static struct language_pass_by_ref_info
gnuv3_pass_by_reference (struct type *type)
{
int fieldnum, fieldelem;
type = check_typedef (type);
+ /* Start with the default values. */
+ struct language_pass_by_ref_info info
+ = default_pass_by_reference (type);
+
+ /* FIXME: Currently, this implementation only fills in the
+ 'trivially-copyable' field to preserve GDB's existing behavior. */
+
/* We're only interested in things that can have methods. */
if (TYPE_CODE (type) != TYPE_CODE_STRUCT
&& TYPE_CODE (type) != TYPE_CODE_UNION)
- return 0;
+ return info;
/* A dynamic class has a non-trivial copy constructor.
See c++98 section 12.8 Copying class objects [class.copy]. */
if (gnuv3_dynamic_class (type))
- return 1;
+ {
+ info.trivially_copyable = false;
+ return info;
+ }
for (fieldnum = 0; fieldnum < TYPE_NFN_FIELDS (type); fieldnum++)
for (fieldelem = 0; fieldelem < TYPE_FN_FIELDLIST_LENGTH (type, fieldnum);
/* If we've found a destructor, we must pass this by reference. */
if (name[0] == '~')
- return 1;
+ {
+ info.trivially_copyable = false;
+ return info;
+ }
/* If the mangled name of this method doesn't indicate that it
is a constructor, we're not interested.
if (TYPE_CODE (arg_type) == TYPE_CODE_REF)
{
- struct type *arg_target_type;
-
- arg_target_type = check_typedef (TYPE_TARGET_TYPE (arg_type));
+ struct type *arg_target_type
+ = check_typedef (TYPE_TARGET_TYPE (arg_type));
if (class_types_same_p (arg_target_type, type))
- return 1;
+ {
+ info.trivially_copyable = false;
+ return info;
+ }
}
}
}
about recursive loops here, since we are only looking at members
of complete class type. Also ignore any static members. */
for (fieldnum = 0; fieldnum < TYPE_NFIELDS (type); fieldnum++)
- if (! field_is_static (&TYPE_FIELD (type, fieldnum))
- && gnuv3_pass_by_reference (TYPE_FIELD_TYPE (type, fieldnum)))
- return 1;
+ if (!field_is_static (&TYPE_FIELD (type, fieldnum)))
+ {
+ struct language_pass_by_ref_info field_info
+ = gnuv3_pass_by_reference (TYPE_FIELD_TYPE (type, fieldnum));
+ if (!field_info.trivially_copyable)
+ {
+ info.trivially_copyable = false;
+ return info;
+ }
+ }
- return 0;
+ return info;
}
static void
args[i] = value_arg_coerce (gdbarch, args[i],
param_type, prototyped);
- if (param_type != NULL && language_pass_by_reference (param_type))
+ if (param_type != NULL
+ && !(language_pass_by_reference (param_type).trivially_copyable))
args[i] = value_addr (args[i]);
}
return NULL;
}
-/* Return non-zero if TYPE should be passed (and returned) by
- reference at the language level. */
-int
+/* Return information about whether TYPE should be passed
+ (and returned) by reference at the language level. */
+
+struct language_pass_by_ref_info
language_pass_by_reference (struct type *type)
{
return current_language->la_pass_by_reference (type);
}
-/* Return zero; by default, types are passed by value at the language
- level. The target ABI may pass or return some structs by reference
- independent of this. */
-int
+/* Return a default struct that provides pass-by-reference information
+ about the given TYPE. Languages should update the default values
+ as appropriate. */
+
+struct language_pass_by_ref_info
default_pass_by_reference (struct type *type)
{
- return 0;
+ return {};
}
/* Return the default string containing the list of characters
struct type *bool_type_default;
};
+/* In a language (particularly C++) a function argument of an aggregate
+ type (i.e. class/struct/union) may be implicitly passed by reference
+ even though it is declared a call-by-value argument in the source.
+ The struct below puts together necessary information for GDB to be
+ able to detect and carry out pass-by-reference semantics for a
+ particular type. This type is referred as T in the inlined comments
+ below.
+
+ The default values of the fields are chosen to give correct semantics
+ for primitive types and for simple aggregate types, such as
+
+ class T {
+ int x;
+ }; */
+
+struct language_pass_by_ref_info
+{
+ /* True if an argument of type T can be passed to a function by value
+ (i.e. not through an implicit reference). False, otherwise. */
+ bool trivially_copyable = true;
+
+ /* True if a copy of a value of type T can be initialized by
+ memcpy'ing the value bit-by-bit. False, otherwise.
+ E.g. If T has a user-defined copy ctor, this should be false. */
+ bool trivially_copy_constructible = true;
+
+ /* True if a value of type T can be destructed simply by reclaiming
+ the memory area occupied by the value. False, otherwise.
+ E.g. If T has a user-defined destructor, this should be false. */
+ bool trivially_destructible = true;
+
+ /* True if it is allowed to create a copy of a value of type T.
+ False, otherwise.
+ E.g. If T has a deleted copy ctor, this should be false. */
+ bool copy_constructible = true;
+
+ /* True if a value of type T can be destructed. False, otherwise.
+ E.g. If T has a deleted destructor, this should be false. */
+ bool destructible = true;
+};
+
/* Structure tying together assorted information about a language. */
struct language_defn
struct ui_file *stream,
const struct value_print_options *options);
- /* Return non-zero if TYPE should be passed (and returned) by
- reference at the language level. */
- int (*la_pass_by_reference) (struct type *type);
+ /* Return information about whether TYPE should be passed
+ (and returned) by reference at the language level. */
+ struct language_pass_by_ref_info (*la_pass_by_reference)
+ (struct type *type);
/* Return an expression that can be used for a location
watchpoint. TYPE is a pointer type that points to the memory
struct ui_file *stream,
const struct value_print_options *options);
-/* Return non-zero if TYPE should be passed (and returned) by
- reference at the language level. */
-int language_pass_by_reference (struct type *type);
+/* Return information about whether TYPE should be passed
+ (and returned) by reference at the language level. */
+struct language_pass_by_ref_info language_pass_by_reference (struct type *type);
-/* Return zero; by default, types are passed by value at the language
- level. The target ABI may pass or return some structs by reference
- independent of this. */
-int default_pass_by_reference (struct type *type);
+/* Return a default struct that provides pass-by-reference information
+ about the given TYPE. Languages should update the default values
+ as appropriate. */
+struct language_pass_by_ref_info default_pass_by_reference (struct type *type);
/* The default implementation of la_print_typedef. */
void default_print_typedef (struct type *type, struct symbol *new_symbol,
if (type != NULL)
{
type = check_typedef (type);
- if (language_pass_by_reference (type))
+ if (!(language_pass_by_reference (type).trivially_copyable))
return RETURN_VALUE_STRUCT_CONVENTION;
}
}
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