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From: "luis at luismarques dot eu" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug other/95722] New: libatomic crashes on __atomic_load of const
 object
Date: Wed, 17 Jun 2020 14:55:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D95722

            Bug ID: 95722
           Summary: libatomic crashes on __atomic_load of const object
           Product: gcc
           Version: 10.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
          Assignee: unassigned at gcc dot gnu.org
          Reporter: luis at luismarques dot eu
  Target Milestone: ---

With this code in `test.c`:

```
struct S {
    int x;
    int y;
    int z;
};

int main() {
    __attribute__((aligned(16))) static const _Atomic struct S a;
    struct S b;
    b =3D a;
}
```

On x86_64 I get:

```
$ gcc test.c -latomic && ./a.out=20
Segmentation fault (core dumped)
```

It crashes on a `lock cmpxchg16b` with the address of `a`, so I imagine the
libatomic implementation is dispatching to an optimized __atomic_load case
where the code assumes it can get a (mutable) lock from the object itself, =
and
when it tries to acquire that lock it writes to `.rodata`, causing the cras=
h.=