http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51410
Bug #: 51410
Summary: duplicate variable DIE
Classification: Unclassified
Product: gcc
Version: 4.6.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: m...@gcc.gnu.org
CC: tro...@redhat.com
This used to confuse systemtap, it has been fixed by searching the symbol table
to find the address of a variable if no location description is available if
the var DIE is marked external. It can certainly be argued that systemtap
should just search harder and find the other var DIE that does contain a
location description. But it sure is confusing IMHO.
Given the following source code:
int x;
int main(int argc, char **argv)
{
return x;
}
compiled with gcc (GCC) 4.6.1 20110908 (Red Hat 4.6.1-9)
$ gcc -g -O2 -o /tmp/x x.c
produces the following .debug_info:
DWARF section [28] '.debug_info' at offset 0x6a5:
[Offset]
Compilation unit at offset 0:
Version: 3, Abbreviation section offset: 0, Address size: 4, Offset size: 4
[ b] compile_unit
producer (strp) "GNU C 4.6.1 20110908 (Red Hat 4.6.1-9)"
language (data1) ISO C89 (1)
name (string) "x.c"
comp_dir (strp) "/home/mark/src/tests"
ranges (data4) range list [ 0]
low_pc (addr) 0000000000
entry_pc (addr) 0000000000
stmt_list (data4) 0
[ 29] subprogram
external (flag) Yes
name (strp) "main"
decl_file (data1) 1
decl_line (data1) 3
prototyped (flag) Yes
type (ref4) [ 61]
low_pc (addr) 0x080482e0 <main>
high_pc (addr) 0x080482e6
frame_base (block1) [ 0] call_frame_cfa
sibling (ref4) [ 61]
[ 44] formal_parameter
name (strp) "argc"
decl_file (data1) 1
decl_line (data1) 3
type (ref4) [ 61]
location (block1) [ 0] fbreg 0
[ 52] formal_parameter
name (strp) "argv"
decl_file (data1) 1
decl_line (data1) 3
type (ref4) [ 68]
location (block1) [ 0] fbreg 4
[ 61] base_type
byte_size (data1) 4
encoding (data1) signed (5)
name (string) "int"
[ 68] pointer_type
byte_size (data1) 4
type (ref4) [ 6e]
[ 6e] pointer_type
byte_size (data1) 4
type (ref4) [ 74]
[ 74] base_type
byte_size (data1) 1
encoding (data1) signed_char (6)
name (strp) "char"
[ 7b] variable
name (string) "x"
decl_file (data1) 1
decl_line (data1) 1
type (ref4) [ 61]
external (flag) Yes
declaration (flag) Yes
[ 86] variable
name (string) "x"
decl_file (data1) 1
decl_line (data1) 1
type (ref4) [ 61]
external (flag) Yes
location (block1) [ 0] addr 0x8049634
<x>
Note that there are two variable DIEs for x, 7b and 86, neither of which is
references in the rest of the CU. Since 86 doesn't refer to 7b, it isn't clear
to me how a consumer can know this is the same variable. In any case it seems
redundant to have both, even if the consumer is supposed to discard the one
marked as declaration.
This isn't an issue for static variables, which will have only one var DIE. It
is also a regression compared to gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-51)
which would produce only one variable DIE for x.
