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Re: GDB and C++: handling of POD/non-POD objects
- From: Daniel Jacobowitz <drow at false dot org>
- To: Christophe LYON <christophe dot lyon at st dot com>
- Cc: gdb at sourceware dot org
- Date: Mon, 20 Jun 2005 09:57:06 -0400
- Subject: Re: GDB and C++: handling of POD/non-POD objects
- References: <42B68205.38424254@st.com>
On Mon, Jun 20, 2005 at 10:44:53AM +0200, Christophe LYON wrote:
>
> Hi all,
>
> I am working on C++ support in our GDB port, and
> currently fixing bugs with the handling of how
> objects are returned by function called "by hand".
>
> Our compiler conforms to the common vendor ABI,
> and I have to distinguish POD and non-POD objects.
> For the latter, a hidden parameter is supplied
> by the caller, which is a pointer to a memory
> area to store the return value.
>
> I have looked in GDB how POD and non-POD objects
> are handled and found only a few lines in the
> AMD64 port. I have to mention that it looks buggy,
> as non-POD objects are equivalent to objects
> which have base classes, which is not the right
> definition.
>
> I am surprised that no other target already has
> code to handle this: is it because every other
> target always needs the hidden pointer parameter
> to handle object return, whether POD or non-POD?
The code in the AMD64 port is for a different purpose. What you're
describing needs to live at a higher level, in the architecture
independent code.
Here's a patch; I haven't updated or tested it in a while. I need to
rework it, and I need to check a couple of existing disabled tests that
it probably affects; I just haven't had the time yet.
--
Daniel Jacobowitz
CodeSourcery, LLC
Index: gdb-6.3/gdb/infcall.c
===================================================================
--- gdb-6.3.orig/gdb/infcall.c 2004-10-08 04:15:56.000000000 -0400
+++ gdb-6.3/gdb/infcall.c 2004-11-10 12:30:07.000000000 -0500
@@ -36,6 +36,7 @@
#include "gdb_string.h"
#include "infcall.h"
#include "dummy-frame.h"
+#include "cp-abi.h"
/* NOTE: cagney/2003-04-16: What's the future of this code?
@@ -297,8 +298,8 @@ call_function_by_hand (struct value *fun
{
CORE_ADDR sp;
CORE_ADDR dummy_addr;
- struct type *value_type;
- unsigned char struct_return;
+ struct type *value_type, *target_value_type;
+ unsigned char struct_return = 0, cp_struct_return = 0;
CORE_ADDR struct_addr = 0;
struct regcache *retbuf;
struct cleanup *retbuf_cleanup;
@@ -312,6 +313,7 @@ call_function_by_hand (struct value *fun
struct regcache *caller_regcache;
struct cleanup *caller_regcache_cleanup;
struct frame_id dummy_id;
+ struct cleanup *args_cleanup;
if (!target_has_execution)
noprocess ();
@@ -410,10 +412,31 @@ call_function_by_hand (struct value *fun
using_gcc = (b == NULL ? 2 : BLOCK_GCC_COMPILED (b));
}
- /* Are we returning a value using a structure return or a normal
- value return? */
+ /* Are we returning a value using a structure return (passing a
+ hidden argument pointing to storage) or a normal value return?
+ There are two cases: C++ ABI mandated structure return and
+ target ABI structure return. The variable STRUCT_RETURN only
+ describes the latter. The C++ version is handled by passing
+ the return location as the first parameter to the function,
+ even preceding "this". This is different from the target
+ ABI version, which is target-specific; for instance, on ia64
+ the first argument is passed in out0 but the hidden structure
+ return pointer would normally be passed in r8. */
- struct_return = using_struct_return (value_type, using_gcc);
+ if (current_language->la_language == language_cplus
+ && cp_pass_by_reference (value_type))
+ {
+ cp_struct_return = 1;
+
+ /* Tell the target specific argument pushing routine not to
+ expect a value. */
+ target_value_type = builtin_type_void;
+ }
+ else
+ {
+ struct_return = using_struct_return (value_type, using_gcc);
+ target_value_type = value_type;
+ }
/* Determine the location of the breakpoint (and possibly other
stuff) that the called function will return to. The SPARC, for a
@@ -432,7 +455,7 @@ call_function_by_hand (struct value *fun
if (INNER_THAN (1, 2))
{
sp = push_dummy_code (current_gdbarch, sp, funaddr,
- using_gcc, args, nargs, value_type,
+ using_gcc, args, nargs, target_value_type,
&real_pc, &bp_addr);
dummy_addr = sp;
}
@@ -440,7 +463,7 @@ call_function_by_hand (struct value *fun
{
dummy_addr = sp;
sp = push_dummy_code (current_gdbarch, sp, funaddr,
- using_gcc, args, nargs, value_type,
+ using_gcc, args, nargs, target_value_type,
&real_pc, &bp_addr);
}
break;
@@ -507,9 +530,15 @@ call_function_by_hand (struct value *fun
param_type = TYPE_FIELD_TYPE (ftype, i);
else
param_type = NULL;
-
+
args[i] = value_arg_coerce (args[i], param_type, prototyped);
+ /* FIXME: Is current_language the right language? */
+ if (current_language->la_language == language_cplus
+ && param_type != NULL
+ && cp_pass_by_reference (param_type))
+ args[i] = value_addr (args[i]);
+
/* elz: this code is to handle the case in which the function
to be called has a pointer to function as parameter and the
corresponding actual argument is the address of a function
@@ -607,7 +636,7 @@ You must use a pointer to function type
stack, if necessary. Make certain that the value is correctly
aligned. */
- if (struct_return)
+ if (struct_return || cp_struct_return)
{
int len = TYPE_LENGTH (value_type);
if (INNER_THAN (1, 2))
@@ -632,6 +661,22 @@ You must use a pointer to function type
}
}
+ if (cp_struct_return)
+ {
+ struct value **new_args;
+
+ /* Add the new argument to the front of the argument list. */
+ new_args = xmalloc (sizeof (struct value *) * (nargs + 1));
+ new_args[0] = value_from_pointer (lookup_pointer_type (value_type),
+ struct_addr);
+ memcpy (&new_args[1], &args[0], sizeof (struct value *) * nargs);
+ args = new_args;
+ nargs++;
+ args_cleanup = make_cleanup (xfree, args);
+ }
+ else
+ args_cleanup = make_cleanup (null_cleanup, NULL);
+
/* Create the dummy stack frame. Pass in the call dummy address as,
presumably, the ABI code knows where, in the call dummy, the
return address should be pointed. */
@@ -649,6 +694,8 @@ You must use a pointer to function type
else
error ("This target does not support function calls");
+ do_cleanups (args_cleanup);
+
/* Set up a frame ID for the dummy frame so we can pass it to
set_momentary_breakpoint. We need to give the breakpoint a frame
ID so that the breakpoint code can correctly re-identify the
@@ -839,11 +886,7 @@ the function call).", name);
/* Figure out the value returned by the function, return that. */
{
struct value *retval;
- if (TYPE_CODE (value_type) == TYPE_CODE_VOID)
- /* If the function returns void, don't bother fetching the
- return value. */
- retval = allocate_value (value_type);
- else if (struct_return)
+ if (struct_return || cp_struct_return)
/* NOTE: cagney/2003-09-27: This assumes that PUSH_DUMMY_CALL
has correctly stored STRUCT_ADDR in the target. In the past
that hasn't been the case, the old MIPS PUSH_ARGUMENTS
@@ -853,6 +896,10 @@ the function call).", name);
"struct return convention", check that PUSH_DUMMY_CALL isn't
playing tricks. */
retval = value_at (value_type, struct_addr, NULL);
+ else if (TYPE_CODE (value_type) == TYPE_CODE_VOID)
+ /* If the function returns void, don't bother fetching the
+ return value. */
+ retval = allocate_value (value_type);
else
{
/* This code only handles "register convention". */
Index: gdb-6.3/gdb/cp-abi.h
===================================================================
--- gdb-6.3.orig/gdb/cp-abi.h 2003-04-12 13:41:25.000000000 -0400
+++ gdb-6.3/gdb/cp-abi.h 2004-11-10 12:30:07.000000000 -0500
@@ -1,7 +1,7 @@
/* Abstraction of various C++ ABI's we support, and the info we need
to get from them.
Contributed by Daniel Berlin <dberlin@redhat.com>
- Copyright 2001 Free Software Foundation, Inc.
+ Copyright 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
This file is part of GDB.
@@ -145,6 +145,10 @@ extern struct type *value_rtti_type (str
extern int baseclass_offset (struct type *type, int index, char *valaddr,
CORE_ADDR address);
+/* 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);
+
struct cp_abi_ops
{
const char *shortname;
@@ -162,6 +166,7 @@ struct cp_abi_ops
int *using_enc);
int (*baseclass_offset) (struct type *type, int index, char *valaddr,
CORE_ADDR address);
+ int (*pass_by_reference) (struct type *type);
};
Index: gdb-6.3/gdb/cp-abi.c
===================================================================
--- gdb-6.3.orig/gdb/cp-abi.c 2003-11-26 17:04:00.000000000 -0500
+++ gdb-6.3/gdb/cp-abi.c 2004-11-10 12:30:07.000000000 -0500
@@ -1,5 +1,5 @@
/* Generic code for supporting multiple C++ ABI's
- Copyright 2001, 2002, 2003 Free Software Foundation, Inc.
+ Copyright 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
This file is part of GDB.
@@ -94,6 +94,14 @@ value_rtti_type (struct value *v, int *f
return (*current_cp_abi.rtti_type) (v, full, top, using_enc);
}
+int
+cp_pass_by_reference (struct type *type)
+{
+ if ((current_cp_abi.pass_by_reference) == NULL)
+ return 0;
+ return (*current_cp_abi.pass_by_reference) (type);
+}
+
/* Set the current C++ ABI to SHORT_NAME. */
static int
Index: gdb-6.3/gdb/gnu-v3-abi.c
===================================================================
--- gdb-6.3.orig/gdb/gnu-v3-abi.c 2004-03-15 15:38:08.000000000 -0500
+++ gdb-6.3/gdb/gnu-v3-abi.c 2004-11-10 12:30:07.000000000 -0500
@@ -1,7 +1,7 @@
/* Abstraction of GNU v3 abi.
Contributed by Jim Blandy <jimb@redhat.com>
- Copyright 2001, 2002, 2003 Free Software Foundation, Inc.
+ Copyright 2001, 2002, 2003, 2004 Free Software Foundation, Inc.
This file is part of GDB.
@@ -419,6 +419,84 @@ gnuv3_baseclass_offset (struct type *typ
return base_offset;
}
+/* Return nonzero if a type should be passed by reference.
+
+ 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
+ caller must make a copy (by calling the copy constructor if there
+ is one or perform the copy itself otherwise), pass the address of
+ the copy, and then destroy the temporary (if necessary).
+
+ For return values with non-trivial copy constructors or
+ destructors, space will be allocated in the caller, and a pointer
+ will be passed as the first argument (preceding "this").
+
+ We don't have a bulletproof mechanism for determining whether a
+ constructor or destructor is trivial. For GCC and DWARF2 debug
+ information, we can check the artificial flag.
+
+ We don't do anything with the constructors or destructors yet,
+ but we have to get the argument passing right anyway. */
+static int
+gnuv3_pass_by_reference (struct type *type)
+{
+ int fieldnum, fieldelem, basenum;
+
+ CHECK_TYPEDEF (type);
+
+ /* We're only interested in things that can have methods. */
+ if (TYPE_CODE (type) != TYPE_CODE_STRUCT
+ && TYPE_CODE (type) != TYPE_CODE_CLASS
+ && TYPE_CODE (type) != TYPE_CODE_UNION)
+ return 0;
+
+ for (fieldnum = 0; fieldnum < TYPE_NFN_FIELDS (type); fieldnum++)
+ for (fieldelem = 0; fieldelem < TYPE_FN_FIELDLIST_LENGTH (type, fieldnum);
+ fieldelem++)
+ {
+ struct fn_field *fn = TYPE_FN_FIELDLIST1 (type, fieldnum);
+ char *name = TYPE_FN_FIELDLIST_NAME (type, fieldnum);
+ struct type *fieldtype = TYPE_FN_FIELD_TYPE (fn, fieldelem);
+
+ /* If this function is marked as artificial, it is compiler-generated,
+ and we assume it is trivial. */
+ if (TYPE_FN_FIELD_ARTIFICIAL (fn, fieldelem))
+ continue;
+
+ /* If we've found a destructor, we must pass this by reference. */
+ if (name[0] == '~')
+ return 1;
+
+ /* If the mangled name of this method doesn't indicate that it
+ is a constructor, we're not interested.
+
+ FIXME drow/2004-05-27: We could do this using the name of
+ the method and the name of the class instead of dealing
+ with the mangled name. We don't have a convenient function
+ to strip off both leading scope qualifiers and trailing
+ template arguments yet. */
+ if (!is_constructor_name (TYPE_FN_FIELD_PHYSNAME (fn, fieldelem)))
+ continue;
+
+ /* If this method takes two arguments, and the second argument is
+ a reference to this class, then it is a copy constructor. */
+ if (TYPE_NFIELDS (fieldtype) == 2
+ && TYPE_CODE (TYPE_FIELD_TYPE (fieldtype, 1)) == TYPE_CODE_REF
+ && check_typedef (TYPE_TARGET_TYPE (TYPE_FIELD_TYPE (fieldtype, 1))) == type)
+ return 1;
+ }
+
+ /* Even if all the constructors and destructors were artificial, one
+ of them may have invoked a non-artificial constructor or
+ destructor in a base class. If any base class needs to be passed
+ by reference, so does this class. */
+ for (basenum = 0; basenum < TYPE_N_BASECLASSES (type); basenum++)
+ if (gnuv3_pass_by_reference (TYPE_BASECLASS (type, basenum)))
+ return 1;
+
+ return 0;
+}
+
static void
init_gnuv3_ops (void)
{
@@ -434,6 +512,7 @@ init_gnuv3_ops (void)
gnu_v3_abi_ops.rtti_type = gnuv3_rtti_type;
gnu_v3_abi_ops.virtual_fn_field = gnuv3_virtual_fn_field;
gnu_v3_abi_ops.baseclass_offset = gnuv3_baseclass_offset;
+ gnu_v3_abi_ops.pass_by_reference = gnuv3_pass_by_reference;
}
extern initialize_file_ftype _initialize_gnu_v3_abi; /* -Wmissing-prototypes */
Index: gdb-6.3/gdb/hpacc-abi.c
===================================================================
--- gdb-6.3.orig/gdb/hpacc-abi.c 2003-06-08 14:27:13.000000000 -0400
+++ gdb-6.3/gdb/hpacc-abi.c 2004-11-10 12:30:07.000000000 -0500
@@ -3,7 +3,7 @@
Most of the real code is from HP, i've just fiddled it to fit in
the C++ ABI abstraction framework.
- Copyright 2001 Free Software Foundation, Inc.
+ Copyright 2001, 2002, 2003 Free Software Foundation, Inc.
This file is part of GDB.
Index: gdb-6.3/gdb/Makefile.in
===================================================================
--- gdb-6.3.orig/gdb/Makefile.in 2004-11-10 12:30:06.000000000 -0500
+++ gdb-6.3/gdb/Makefile.in 2004-11-10 12:30:07.000000000 -0500
@@ -2073,7 +2073,7 @@ ia64-tdep.o: ia64-tdep.c $(defs_h) $(inf
infcall.o: infcall.c $(defs_h) $(breakpoint_h) $(target_h) $(regcache_h) \
$(inferior_h) $(gdb_assert_h) $(block_h) $(gdbcore_h) $(language_h) \
$(objfiles_h) $(gdbcmd_h) $(command_h) $(gdb_string_h) $(infcall_h) \
- $(dummy_frame_h)
+ $(dummy_frame_h) $(cp_abi_h)
inf-child.o: inf-child.c $(defs_h) $(regcache_h) $(memattr_h) $(symtab_h) \
$(target_h) $(inferior_h) $(gdb_string_h)
infcmd.o: infcmd.c $(defs_h) $(gdb_string_h) $(symtab_h) $(gdbtypes_h) \
Index: gdb-6.3/gdb/testsuite/gdb.cp/pass-by-ref.exp
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ gdb-6.3/gdb/testsuite/gdb.cp/pass-by-ref.exp 2004-11-11 09:48:00.498518899 -0500
@@ -0,0 +1,38 @@
+# This testcase is part of GDB, the GNU debugger.
+
+# Copyright 2004 Free Software Foundation, Inc.
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+
+# Check that GDB can call C++ functions whose parameters have
+# object type, but are passed by reference.
+
+set testfile "pass-by-ref"
+set srcfile ${testfile}.cc
+set binfile ${objdir}/${subdir}/${testfile}
+if { [gdb_compile "${srcdir}/${subdir}/${srcfile}" "${binfile}" executable {debug}] != "" } {
+ return -1
+}
+
+gdb_exit
+gdb_start
+gdb_reinitialize_dir $srcdir/$subdir
+gdb_load ${binfile}
+
+if ![runto_main] then {
+ return -1
+}
+
+gdb_test "print foo (global_obj)" " = 3" "call function"
Index: gdb-6.3/gdb/testsuite/gdb.cp/pass-by-ref.cc
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ gdb-6.3/gdb/testsuite/gdb.cp/pass-by-ref.cc 2004-11-11 09:44:17.815014667 -0500
@@ -0,0 +1,57 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+ Copyright 2004 Free Software Foundation, Inc.
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 2 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software
+ Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
+ USA. */
+
+class Obj {
+public:
+ Obj ();
+ Obj (const Obj &);
+ ~Obj ();
+ int var[2];
+};
+
+int foo (Obj arg)
+{
+ return arg.var[0] + arg.var[1];
+}
+
+Obj::Obj ()
+{
+ var[0] = 1;
+ var[1] = 2;
+}
+
+Obj::Obj (const Obj &obj)
+{
+ var[0] = obj.var[0];
+ var[1] = obj.var[1];
+}
+
+Obj::~Obj ()
+{
+
+}
+
+Obj global_obj;
+
+int
+main ()
+{
+ int bar = foo (global_obj);
+ return bar;
+}