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gatomic: Fix strict aliasing problems with g_atomic_pointer_{get,set}()

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Casting pointer types around is a bit fiddly when you also end up
dereferencing them. Take advantage of the fact that the
`__atomic_load()` and `__atomic_store()` built-ins are polymorphic, and
use `__typeof__()` to ensure that the atomic pointer macros use the
caller-provided types internally, and hence any type mismatches are
entirely the caller’s fault rather than ours.

This also means that the `__atomic_{load,store}()` built-ins have the
right alignment and width data from the caller-provided types, in case
that’s needed.

Signed-off-by: Philip Withnall <withnall@endlessm.com>
This commit is contained in:
Philip Withnall 2019-10-07 16:23:02 +01:00
parent 81f8d02e4d
commit 3251cce524
1 changed files with 26 additions and 5 deletions
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31
glib/gatomic.h
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@ -103,20 +103,41 @@ G_END_DECLS
__atomic_store ((gint *)(atomic), &gais_temp, __ATOMIC_SEQ_CST); \
}))
#if defined(g_has_typeof)
#define g_atomic_pointer_get(atomic) \
(G_GNUC_EXTENSION ({ \
G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gpointer)); \
gpointer gapg_temp; \
__atomic_load ((gpointer *)(atomic), &gapg_temp, __ATOMIC_SEQ_CST); \
gapg_temp; \
__typeof__(*(atomic)) gapg_temp_newval; \
__typeof__((atomic)) gapg_temp_atomic = (atomic); \
__atomic_load (gapg_temp_atomic, &gapg_temp_newval, __ATOMIC_SEQ_CST); \
gapg_temp_newval; \
}))
#define g_atomic_pointer_set(atomic, newval) \
(G_GNUC_EXTENSION ({ \
G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gpointer)); \
gpointer gaps_temp = (gpointer)(newval); \
__typeof__((atomic)) gaps_temp_atomic = (atomic); \
__typeof__(*(atomic)) gaps_temp_newval = (newval); \
(void) (0 ? (gpointer) *(atomic) : NULL); \
__atomic_store ((gpointer *)(atomic), &gaps_temp, __ATOMIC_SEQ_CST); \
__atomic_store (gaps_temp_atomic, &gaps_temp_newval, __ATOMIC_SEQ_CST); \
}))
#else /* if !defined(g_has_typeof) */
#define g_atomic_pointer_get(atomic) \
(G_GNUC_EXTENSION ({ \
G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gpointer)); \
gpointer gapg_temp_newval; \
gpointer *gapg_temp_atomic = (gpointer *)(atomic); \
__atomic_load (gapg_temp_atomic, &gapg_temp_newval, __ATOMIC_SEQ_CST); \
gapg_temp_newval; \
}))
#define g_atomic_pointer_set(atomic, newval) \
(G_GNUC_EXTENSION ({ \
G_STATIC_ASSERT (sizeof *(atomic) == sizeof (gpointer)); \
gpointer *gaps_temp_atomic = (gpointer *)(atomic); \
gpointer gaps_temp_newval = (gpointer)(newval); \
(void) (0 ? (gpointer) *(atomic) : NULL); \
__atomic_store (gaps_temp_atomic, &gaps_temp_newval, __ATOMIC_SEQ_CST); \
}))
#endif /* !defined(g_has_typeof) */
#else /* defined(__ATOMIC_SEQ_CST) */