mempool: Introduce rseq_mempool_get_max_nr_cpus

[librseq.git] / include / rseq / compiler.h

diff --git a/include/rseq/compiler.h b/include/rseq/compiler.h
index 6b89bfab90dad8b9371ded3e572ba597c87b90e1..9a202cde9246291ec831e216c808d3905867c707 100644 (file)
--- a/include/rseq/compiler.h
+++ b/include/rseq/compiler.h
@@ -7,13 +7,34 @@
  * Work-around asm goto compiler bugs.
  */
 
-#ifndef RSEQ_COMPILER_H
-#define RSEQ_COMPILER_H
+#ifndef _RSEQ_COMPILER_H
+#define _RSEQ_COMPILER_H
 
 #if defined __cplusplus
 # include <type_traits>        /* for std::remove_cv */
 #endif
 
+#define rseq_likely(x)         __builtin_expect(!!(x), 1)
+#define rseq_unlikely(x)       __builtin_expect(!!(x), 0)
+#define rseq_barrier()         __asm__ __volatile__("" : : : "memory")
+
+/*
+ * Instruct the compiler to perform only a single access to a variable
+ * (prohibits merging and refetching). The compiler is also forbidden to reorder
+ * successive instances of RSEQ_ACCESS_ONCE(), but only when the compiler is aware of
+ * particular ordering. Compiler ordering can be ensured, for example, by
+ * putting two RSEQ_ACCESS_ONCE() in separate C statements.
+ *
+ * This macro does absolutely -nothing- to prevent the CPU from reordering,
+ * merging, or refetching absolutely anything at any time.  Its main intended
+ * use is to mediate communication between process-level code and irq/NMI
+ * handlers, all running on the same CPU.
+ */
+#define RSEQ_ACCESS_ONCE(x)    (*(__volatile__  __typeof__(x) *)&(x))
+
+#define RSEQ_WRITE_ONCE(x, v)  __extension__ ({ RSEQ_ACCESS_ONCE(x) = (v); })
+#define RSEQ_READ_ONCE(x)      RSEQ_ACCESS_ONCE(x)
+
 /*
  * gcc prior to 4.8.2 miscompiles asm goto.
  * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58670
@@ -49,7 +70,6 @@
 #define rseq_unqual_scalar_typeof(x)                                   \
        std::remove_cv<std::remove_reference<decltype(x)>::type>::type
 #else
-
 #define rseq_scalar_type_to_expr(type)                                 \
        unsigned type: (unsigned type)0,                                \
        signed type: (signed type)0
@@ -72,4 +92,15 @@
        )
 #endif
 
-#endif  /* RSEQ_COMPILER_H_ */
+/*
+ * RSEQ_PARAM_SELECT_ARG1
+ *
+ * Select second argument. Use inside macros to implement optional last
+ * macro argument, such as:
+ *
+ * #define macro(_a, _b, _c, _optional...) \
+ *     RSEQ_PARAM_SELECT_ARG1(_, ##_optional, do_default_macro())
+ */
+#define RSEQ_PARAM_SELECT_ARG1(_arg0, _arg1, ...) _arg1
+
+#endif  /* _RSEQ_COMPILER_H */