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From: Richard Henderson <richard.henderson@linaro.org>
To: qemu-devel@nongnu.org
Cc: peter.maydell@linaro.org, "Alex Bennée" <alex.bennee@linaro.org>
Subject: [PULL 6/8] include/qemu/lockable: Use _Generic instead of QEMU_GENERIC
Date: Tue, 15 Jun 2021 18:36:27 -0700	[thread overview]
Message-ID: <20210616013629.1458790-7-richard.henderson@linaro.org> (raw)
In-Reply-To: <20210616013629.1458790-1-richard.henderson@linaro.org>

This is both more and less complicated than our expansion
using __builtin_choose_expr and __builtin_types_compatible_p.

The expansion through QEMU_MAKE_LOCKABLE_ doesn't work because
we're not emumerating all of the types within the same _Generic,
which results in errors about unhandled cases.  We must also
handle void* explicitly, so that the NULL constant can be used.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20210614233143.1221879-7-richard.henderson@linaro.org>
---
 include/qemu/lockable.h | 90 +++++++++++++++++++----------------------
 1 file changed, 41 insertions(+), 49 deletions(-)

diff --git a/include/qemu/lockable.h b/include/qemu/lockable.h
index b620023141..86db7cb04c 100644
--- a/include/qemu/lockable.h
+++ b/include/qemu/lockable.h
@@ -24,79 +24,71 @@ struct QemuLockable {
     QemuLockUnlockFunc *unlock;
 };
 
-/* This function gives an error if an invalid, non-NULL pointer type is passed
- * to QEMU_MAKE_LOCKABLE.  For optimized builds, we can rely on dead-code elimination
- * from the compiler, and give the errors already at link time.
- */
-#if defined(__OPTIMIZE__) && !defined(__SANITIZE_ADDRESS__)
-void unknown_lock_type(void *);
-#else
-static inline void unknown_lock_type(void *unused)
-{
-    abort();
-}
-#endif
-
 static inline __attribute__((__always_inline__)) QemuLockable *
 qemu_make_lockable(void *x, QemuLockable *lockable)
 {
-    /* We cannot test this in a macro, otherwise we get compiler
+    /*
+     * We cannot test this in a macro, otherwise we get compiler
      * warnings like "the address of 'm' will always evaluate as 'true'".
      */
     return x ? lockable : NULL;
 }
 
-/* Auxiliary macros to simplify QEMU_MAKE_LOCABLE.  */
-#define QEMU_LOCK_FUNC(x) ((QemuLockUnlockFunc *)    \
-    QEMU_GENERIC(x,                                  \
-                 (QemuMutex *, qemu_mutex_lock),     \
-                 (QemuRecMutex *, qemu_rec_mutex_lock), \
-                 (CoMutex *, qemu_co_mutex_lock),    \
-                 (QemuSpin *, qemu_spin_lock),       \
-                 unknown_lock_type))
+static inline __attribute__((__always_inline__)) QemuLockable *
+qemu_null_lockable(void *x)
+{
+    if (x != NULL) {
+        qemu_build_not_reached();
+    }
+    return NULL;
+}
 
-#define QEMU_UNLOCK_FUNC(x) ((QemuLockUnlockFunc *)  \
-    QEMU_GENERIC(x,                                  \
-                 (QemuMutex *, qemu_mutex_unlock),   \
-                 (QemuRecMutex *, qemu_rec_mutex_unlock), \
-                 (CoMutex *, qemu_co_mutex_unlock),  \
-                 (QemuSpin *, qemu_spin_unlock),     \
-                 unknown_lock_type))
-
-/* In C, compound literals have the lifetime of an automatic variable.
+/*
+ * In C, compound literals have the lifetime of an automatic variable.
  * In C++ it would be different, but then C++ wouldn't need QemuLockable
  * either...
  */
-#define QEMU_MAKE_LOCKABLE_(x) (&(QemuLockable) {     \
-        .object = (x),                               \
-        .lock = QEMU_LOCK_FUNC(x),                   \
-        .unlock = QEMU_UNLOCK_FUNC(x),               \
+#define QML_OBJ_(x, name) (&(QemuLockable) {                            \
+        .object = (x),                                                  \
+        .lock = (QemuLockUnlockFunc *) qemu_ ## name ## _lock,          \
+        .unlock = (QemuLockUnlockFunc *) qemu_ ## name ## _unlock       \
     })
 
-/* QEMU_MAKE_LOCKABLE - Make a polymorphic QemuLockable
+/**
+ * QEMU_MAKE_LOCKABLE - Make a polymorphic QemuLockable
  *
- * @x: a lock object (currently one of QemuMutex, QemuRecMutex, CoMutex, QemuSpin).
+ * @x: a lock object (currently one of QemuMutex, QemuRecMutex,
+ *     CoMutex, QemuSpin).
  *
  * Returns a QemuLockable object that can be passed around
  * to a function that can operate with locks of any kind, or
  * NULL if @x is %NULL.
- */
-#define QEMU_MAKE_LOCKABLE(x)                        \
-    QEMU_GENERIC(x,                                  \
-                 (QemuLockable *, (x)),              \
-                 qemu_make_lockable((x), QEMU_MAKE_LOCKABLE_(x)))
-
-/* QEMU_MAKE_LOCKABLE_NONNULL - Make a polymorphic QemuLockable
  *
- * @x: a lock object (currently one of QemuMutex, QemuRecMutex, CoMutex, QemuSpin).
+ * Note the special case for void *, so that we may pass "NULL".
+ */
+#define QEMU_MAKE_LOCKABLE(x)                                           \
+    _Generic((x), QemuLockable *: (x),                                  \
+             void *: qemu_null_lockable(x),                             \
+             QemuMutex *: qemu_make_lockable(x, QML_OBJ_(x, mutex)),    \
+             QemuRecMutex *: qemu_make_lockable(x, QML_OBJ_(x, rec_mutex)), \
+             CoMutex *: qemu_make_lockable(x, QML_OBJ_(x, co_mutex)),   \
+             QemuSpin *: qemu_make_lockable(x, QML_OBJ_(x, spin)))
+
+/**
+ * QEMU_MAKE_LOCKABLE_NONNULL - Make a polymorphic QemuLockable
+ *
+ * @x: a lock object (currently one of QemuMutex, QemuRecMutex,
+ *     CoMutex, QemuSpin).
  *
  * Returns a QemuLockable object that can be passed around
  * to a function that can operate with locks of any kind.
  */
-#define QEMU_MAKE_LOCKABLE_NONNULL(x)                \
-    QEMU_GENERIC(x,                                  \
-                 (QemuLockable *, (x)),              \
-                 QEMU_MAKE_LOCKABLE_(x))
+#define QEMU_MAKE_LOCKABLE_NONNULL(x)                           \
+    _Generic((x), QemuLockable *: (x),                          \
+                  QemuMutex *: QML_OBJ_(x, mutex),              \
+                  QemuRecMutex *: QML_OBJ_(x, rec_mutex),       \
+                  CoMutex *: QML_OBJ_(x, co_mutex),             \
+                  QemuSpin *: QML_OBJ_(x, spin))
 
 static inline void qemu_lockable_lock(QemuLockable *x)
 {
-- 
2.25.1



  parent reply	other threads:[~2021-06-16  1:44 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-16  1:36 [PULL 0/8] configure: Change to -std=gnu11 Richard Henderson
2021-06-16  1:36 ` [PULL 1/8] configure: Use -std=gnu11 Richard Henderson
2021-06-16  1:36 ` [PULL 2/8] softfloat: Use _Generic instead of QEMU_GENERIC Richard Henderson
2021-06-16  1:36 ` [PULL 3/8] util: Use real functions for thread-posix QemuRecMutex Richard Henderson
2021-06-16  1:36 ` [PULL 4/8] util: Pass file+line to qemu_rec_mutex_unlock_impl Richard Henderson
2021-06-16  1:36 ` [PULL 5/8] util: Use unique type for QemuRecMutex in thread-posix.h Richard Henderson
2021-06-16  1:36 ` Richard Henderson [this message]
2021-06-16  1:36 ` [PULL 7/8] qemu/compiler: Remove QEMU_GENERIC Richard Henderson
2021-06-16  1:36 ` [PULL 8/8] configure: Remove probe for _Static_assert Richard Henderson
2021-06-16  1:51 ` [PULL 0/8] configure: Change to -std=gnu11 no-reply
2021-06-17 14:42 ` Peter Maydell

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