ust-compiler.h: Implement __LTTNG_COMPOUND_LITERAL

Implement __LTTNG_COMPOUND_LITERAL to allow defining a compound literal
with static storage.

Compound literals with static storage are needed by LTTng to implement
nested arrays and sequences in TRACEPOINT_EVENT.

Compound literals are part of the C99 and C11 standards, but not
part of the C++ standards. However, those are supported by both g++ and
clang as C99 extensions when compiling C++ code.

Strict C++11 compliance can be obtained by defining
LTTNG_ALLOCATE_COMPOUND_LITERAL_ON_HEAP before including this header
to allocate those on the heap in C++.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/include/lttng/ust-compiler.h b/include/lttng/ust-compiler.h
index 31eaf73c0139026b9adbb8c87ca7076c0df77125..799bca4291d2802ee590ab628dadc4e956fc1ddf 100644 (file)
--- a/include/lttng/ust-compiler.h
+++ b/include/lttng/ust-compiler.h
@@ -43,4 +43,21 @@
 #  define __lttng_ust_variable_attribute_no_sanitize_address
 #endif
 
+/*
+ * Compound literals with static storage are needed by LTTng.
+ * Compound literals are part of the C99 and C11 standards, but not
+ * part of the C++ standards. However, those are supported by both g++ and
+ * clang. In order to be strictly C++11 compliant, defining
+ * LTTNG_ALLOCATE_COMPOUND_LITERAL_ON_HEAP before including this header
+ * allocates those on the heap in C++.
+ *
+ * Example use:
+ * static struct mystruct *var = __LTTNG_COMPOUND_LITERAL(struct mystruct, { 1, 2, 3 });
+ */
+#if defined (__cplusplus) && defined (LTTNG_ALLOCATE_COMPOUND_LITERAL_ON_HEAP)
+#define __LTTNG_COMPOUND_LITERAL(type, ...)    new (type) __VA_ARGS__
+#else
+#define __LTTNG_COMPOUND_LITERAL(type, ...)    (type[]) { __VA_ARGS__ }
+#endif
+
 #endif /* _LTTNG_UST_COMPILER_H */