Hello,
in debugging a failing GDB test case I've come upon what looks like bad
DWARF-2 debug info being generated by G++.
The problem has to do with typedefs of anonymous structs like:
typedef struct {
int one;
int two;
} tagless_struct;
tagless_struct v_tagless;
This causes the following DWARF-2 to be generated:
.uleb128 0x2 # (DIE (0x6c) DW_TAG_structure_type)
.ascii "<anonymous struct>\0" # DW_AT_name
.byte 0x8 # DW_AT_byte_size
.byte 0x1 # DW_AT_decl_file (xxx.ii)
.byte 0x1 # DW_AT_decl_line
.4byte 0xa4 # DW_AT_sibling
.uleb128 0x3 # (DIE (0x87) DW_TAG_member)
.ascii "one\0" # DW_AT_name
.byte 0x1 # DW_AT_decl_file (xxx.ii)
.byte 0x2 # DW_AT_decl_line
.4byte 0xa4 # DW_AT_type
.byte 0x2 # DW_AT_data_member_location
.byte 0x23 # DW_OP_plus_uconst
.uleb128 0x0
.uleb128 0x3 # (DIE (0x95) DW_TAG_member)
.ascii "two\0" # DW_AT_name
.byte 0x1 # DW_AT_decl_file (xxx.ii)
.byte 0x3 # DW_AT_decl_line
.4byte 0xa4 # DW_AT_type
.byte 0x2 # DW_AT_data_member_location
.byte 0x23 # DW_OP_plus_uconst
.uleb128 0x4
.byte 0x0 # end of children of DIE 0x6c
.uleb128 0x4 # (DIE (0xa4) DW_TAG_base_type)
.byte 0x4 # DW_AT_byte_size
.byte 0x5 # DW_AT_encoding
.ascii "int\0" # DW_AT_name
.uleb128 0x5 # (DIE (0xab) DW_TAG_variable)
.ascii "v_tagless\0" # DW_AT_name
.byte 0x1 # DW_AT_decl_file (xxx.ii)
.byte 0x5 # DW_AT_decl_line
.4byte 0x6c # DW_AT_type
.byte 0x1 # DW_AT_external
.byte 0x5 # DW_AT_location
.byte 0x3 # DW_OP_addr
.4byte v_tagless
Note how the v_tagless variable records DIE 0x6c as type, which is
the anonymous struct -- the typedef is completely missing.
This is incorrect; we should see "tagless_struct" as type of
"v_tagless".
The reason for this appears to be the following optimization in
cp/decl.c (grokdeclarator):
/* If the user declares "typedef struct {...} foo" then the
struct will have an anonymous name. Fill that name in now.
Nothing can refer to it, so nothing needs know about the name
change. */
if (type != error_mark_node
&& unqualified_id
&& TYPE_NAME (type)
&& TREE_CODE (TYPE_NAME (type)) == TYPE_DECL
&& TYPE_ANONYMOUS_P (type)
/* Don't do this if there are attributes. */
&& (!attrlist || !*attrlist)
&& cp_type_quals (type) == TYPE_UNQUALIFIED)
{
tree oldname = TYPE_NAME (type);
tree t;
/* Replace the anonymous name with the real name everywhere. */
for (t = TYPE_MAIN_VARIANT (type); t; t = TYPE_NEXT_VARIANT (t))
if (TYPE_NAME (t) == oldname)
TYPE_NAME (t) = decl;
This attempts to change the <anonymous struct> name to the typedef name.
However, it comes too late. The original anonymous struct type has already
run through rest_of_type_compilation at this stage, which has already called
dwarf2out_decl on it. This in turn has already allocated the DIE and set up
the name information. Changing TYPE_NAME afterwards has no effect on the
debug data any more.
Any suggestions how to fix this?
Thanks,
Ulrich
--
Dr. Ulrich Weigand
GNU Toolchain for Linux on System z and Cell BE
[EMAIL PROTECTED]
