https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105089
Bug ID: 105089
Summary: CTF for a defined extern variable is ambiguous
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: ibhagat at gcc dot gnu.org
Target Milestone: ---
$ cat extern.c
extern const char a[];
const char a[] = "testme";
$ gcc -gctf -dA -S extern.c
excerpt from extern.s:
.long 0x5 # objtinfo_var_type
.long 0x8 # objtinfo_var_type
.long 0xb # objtinfo_name
.long 0x1f # objtinfo_name
.long 0xb # ctv_name
.long 0x5 # ctv_typeidx
.long 0x1f # ctv_name
.long 0x8 # ctv_typeidx
There are TWO CTF variable records (two ctv_name, each with a ctv_typeidx).
Further, two CTF objects records as well.
$ gcc -gctf -c extern.c
$ objdump --ctf=.ctf extern.o
shows:
Variables:
a -> 8: const const char [7] (size 0x7) -> 7: const char [7] (size 0x7)
a -> 5: const const char [0] (size 0x0) -> 4: const char [0] (size 0x0)
Types:
1: char (size 0x1)
[0x0] (ID 0x1) (kind 1) char (aligned at 0x1, format 0x3, offset:bits
0x0:0x8)
2: const char (size 0x1) -> 1: char (size 0x1)
[0x0] (ID 0x2) (kind 12) const char (aligned at 0x1)
3: void (size 0x0)
[0x0] (ID 0x3) (kind 1) void (aligned at 0x0, format 0x1, offset:bits
0x0:0x0)
4: const char [0] (size 0x0)
[0x0] (ID 0x4) (kind 4) const char [0] (aligned at 0x1)
5: const const char [0] (size 0x0) -> 4: const char [0] (size 0x0)
[0x0] (ID 0x5) (kind 12) const const char [0] (aligned at 0x1)
6: long unsigned int (size 0x8)
[0x0] (ID 0x6) (kind 1) long unsigned int (aligned at 0x8, format 0x0,
offset:bits 0x0:0x40)
7: const char [7] (size 0x7)
[0x0] (ID 0x7) (kind 4) const char [7] (aligned at 0x1)
8: const const char [7] (size 0x7) -> 7: const char [7] (size 0x7)
[0x0] (ID 0x8) (kind 12) const const char [7] (aligned at 0x1)
Strings:
0:
1: char
6: void
b: a
d: long unsigned int
1f: a
...
Note, two entries in the "Variables:" sub-section, and two strings "a" for the
variable name in the "Strings:" sub-section.
In the above case, the compiler must emit only one entry for the variable a
with type specified as const char [7].
Note that, CTF format cannot differentiate between a non-defining extern
variable declaration vs. a defining variable declaration (unlike DWARF). So,
emitting two CTF variable records, one for the non-defining decl and another
for the defining decl will create ambiguity for the linker/CTF reader.
