https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81439
Bug ID: 81439
Summary: -Wlto-type-mismatch with flexible array in struct
Product: gcc
Version: 6.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: lto
Assignee: unassigned at gcc dot gnu.org
Reporter: halbert at halwitz dot org
CC: marxin at gcc dot gnu.org
Target Milestone: ---
Created attachment 41756
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41756&action=edit
all example source files in description
I'm getting a -Wlto-type-mismatch warning with a struct that ends with a
flexible array, declared in one file and initialized in another. I do NOT get a
warning with a simple flexible array in the same situation.
Since the plain flexible array does not generate a warning, I think perhaps LTO
should not generate a warning for the struct case either, since the idea of the
flexible array is to allow it to be of any length when initialized.
As a workaround, I've tried suppressing the warning with #pragmas in the source
code, but I guess they don't pass through to LTO.
(tested with arm-none-eabi-gcc 6.3.1, but I see the same issue with native gcc
6.3.0)
HAS WARNING:
ab_struct.h
-----------
typedef struct {
int i;
int ints[];
} struct_t;
a_struct.c
----------
#include "ab_struct.h"
extern struct_t my_struct;
int main() {
return my_struct.ints[0];
}
b_struct.c
----------
#include "ab_struct.h"
struct_t my_struct = {
20,
{ 1, 2 }
};
$ arm-none-eabi-gcc -flto -Wlto-type-mismatch a_struct.c b_struct.c -o foo
a_struct.c:3:17: warning: size of 'my_struct' differ from the size of original
declaration [-Wlto-type-mismatch]
extern struct_t my_struct;
^
b_struct.c:3:10: note: 'my_struct' was previously declared here
struct_t my_struct = {
-----------------------------------------------------------------------------
NO WARNING with this plain flexible array, not in a struct:
a_array.c
---------
extern int ia[];
int main() {
return ia[0];
}
b_array.c
---------
int ia[] = { 1, 2 };
$ arm-none-eabi-gcc -flto -Wlto-type-mismatch a_array.c b_array.c -o foo
[no warning]
