https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87578
Bug ID: 87578
Summary: attribute transparent_union silently accepted but
ignored on typedef
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: msebor at gcc dot gnu.org
Target Milestone: ---
GCC (in C mode) silently accepts but discards attribute transparent_union on a
typedef. The attribute handler is never invoked on the typedef (attributes is
null in decl_attributes when the typedef definition is being processed,
suggesting this is a general problem).
G++ diagnoses the typedef definition with -Wattributes. Clang diagnoses it in
both C and C++ modes as well, although with -Wignored-attributes:
x.c:13:31: warning: transparent_union attribute can only be applied to a union
definition; attribute ignored [-Wignored-attributes]
$ cat x.c && gcc -S -Wall -Wextra x.c
union __attribute__ ((transparent_union)) A
{
int *ip;
double *dp;
};
union B
{
int *ip;
double *dp;
};
typedef union __attribute__ ((transparent_union)) B TB; // silently accepted
void f (union A);
void g (TB);
void h (void)
{
f ((int*)0); // okay
f ((double*)0); // okay
g ((int*)0); // error
g ((double*)0); // error
}
x.c: In function ‘h’:
x.c:23:6: error: incompatible type for argument 1 of ‘g’
23 | g ((int*)0); // error
| ^~~~~~~
| |
| int *
x.c:16:9: note: expected ‘TB’ {aka ‘union B’} but argument is of type ‘int *’
16 | void g (TB);
| ^~
x.c:24:6: error: incompatible type for argument 1 of ‘g’
24 | g ((double*)0); // error
| ^~~~~~~~~~
| |
| double *
x.c:16:9: note: expected ‘TB’ {aka ‘union B’} but argument is of type ‘double
*’
16 | void g (TB);
| ^~
