The typeof_strip_qual() is most useful for the atomic fetch-and-modify
operations in atomic.h, but it can be used elsewhere as well. For example,
QAPI_LIST_LENGTH() assumes that the argument is not const, which is not a
requirement.
Move the macro to compiler.h and, while at it, move it under #ifndef
__cplusplus to emphasize that it uses C-only constructs. A C++ version
of typeof_strip_qual() using type traits is possible[1], but beyond the
scope of this patch because the little C++ code that is in QEMU does not
use QAPI.
The patch was tested by changing the declaration of strv_from_str_list()
in qapi/qapi-type-helpers.c to:
char **strv_from_str_list(const strList *const list)
This is valid C code, and it fails to compile without this change.
[1] https://lore.kernel.org/qemu-devel/20240624205647.112034-1-f...@google.com/
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
include/qapi/util.h | 2 +-
include/qemu/atomic.h | 42 -------------------------------------
include/qemu/compiler.h | 46 +++++++++++++++++++++++++++++++++++++++++
3 files changed, 47 insertions(+), 43 deletions(-)
diff --git a/include/qapi/util.h b/include/qapi/util.h
index 20dfea8a545..b8254247b8d 100644
--- a/include/qapi/util.h
+++ b/include/qapi/util.h
@@ -62,7 +62,7 @@ int parse_qapi_name(const char *name, bool complete);
#define QAPI_LIST_LENGTH(list) \
({ \
size_t _len = 0; \
- typeof(list) _tail; \
+ typeof_strip_qual(list) _tail; \
for (_tail = list; _tail != NULL; _tail = _tail->next) { \
_len++; \
} \
diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h
index 99110abefb3..dc4118ddd9e 100644
--- a/include/qemu/atomic.h
+++ b/include/qemu/atomic.h
@@ -20,48 +20,6 @@
/* Compiler barrier */
#define barrier() ({ asm volatile("" ::: "memory"); (void)0; })
-/* The variable that receives the old value of an atomically-accessed
- * variable must be non-qualified, because atomic builtins return values
- * through a pointer-type argument as in __atomic_load(&var, &old, MODEL).
- *
- * This macro has to handle types smaller than int manually, because of
- * implicit promotion. int and larger types, as well as pointers, can be
- * converted to a non-qualified type just by applying a binary operator.
- */
-#define typeof_strip_qual(expr)
\
- typeof(
\
- __builtin_choose_expr(
\
- __builtin_types_compatible_p(typeof(expr), bool) ||
\
- __builtin_types_compatible_p(typeof(expr), const bool) ||
\
- __builtin_types_compatible_p(typeof(expr), volatile bool) ||
\
- __builtin_types_compatible_p(typeof(expr), const volatile bool),
\
- (bool)1,
\
- __builtin_choose_expr(
\
- __builtin_types_compatible_p(typeof(expr), signed char) ||
\
- __builtin_types_compatible_p(typeof(expr), const signed char) ||
\
- __builtin_types_compatible_p(typeof(expr), volatile signed char) ||
\
- __builtin_types_compatible_p(typeof(expr), const volatile signed
char), \
- (signed char)1,
\
- __builtin_choose_expr(
\
- __builtin_types_compatible_p(typeof(expr), unsigned char) ||
\
- __builtin_types_compatible_p(typeof(expr), const unsigned char) ||
\
- __builtin_types_compatible_p(typeof(expr), volatile unsigned char) ||
\
- __builtin_types_compatible_p(typeof(expr), const volatile unsigned
char), \
- (unsigned char)1,
\
- __builtin_choose_expr(
\
- __builtin_types_compatible_p(typeof(expr), signed short) ||
\
- __builtin_types_compatible_p(typeof(expr), const signed short) ||
\
- __builtin_types_compatible_p(typeof(expr), volatile signed short) ||
\
- __builtin_types_compatible_p(typeof(expr), const volatile signed
short), \
- (signed short)1,
\
- __builtin_choose_expr(
\
- __builtin_types_compatible_p(typeof(expr), unsigned short) ||
\
- __builtin_types_compatible_p(typeof(expr), const unsigned short) ||
\
- __builtin_types_compatible_p(typeof(expr), volatile unsigned short) ||
\
- __builtin_types_compatible_p(typeof(expr), const volatile unsigned
short), \
- (unsigned short)1,
\
- (expr)+0))))))
-
#ifndef __ATOMIC_RELAXED
#error "Expecting C11 atomic ops"
#endif
diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
index c797f0d4572..554c5ce7df7 100644
--- a/include/qemu/compiler.h
+++ b/include/qemu/compiler.h
@@ -227,4 +227,50 @@
#define SECOND_ARG(first, second, ...) second
#define IS_EMPTY_(junk_maybecomma) SECOND_ARG(junk_maybecomma 1, 0)
+#ifndef __cplusplus
+/*
+ * Useful in macros that need to declare temporary variables. For example,
+ * the variable that receives the old value of an atomically-accessed
+ * variable must be non-qualified, because atomic builtins return values
+ * through a pointer-type argument as in __atomic_load(&var, &old, MODEL).
+ *
+ * This macro has to handle types smaller than int manually, because of
+ * implicit promotion. int and larger types, as well as pointers, can be
+ * converted to a non-qualified type just by applying a binary operator.
+ */
+#define typeof_strip_qual(expr)
\
+ typeof(
\
+ __builtin_choose_expr(
\
+ __builtin_types_compatible_p(typeof(expr), bool) ||
\
+ __builtin_types_compatible_p(typeof(expr), const bool) ||
\
+ __builtin_types_compatible_p(typeof(expr), volatile bool) ||
\
+ __builtin_types_compatible_p(typeof(expr), const volatile bool),
\
+ (bool)1,
\
+ __builtin_choose_expr(
\
+ __builtin_types_compatible_p(typeof(expr), signed char) ||
\
+ __builtin_types_compatible_p(typeof(expr), const signed char) ||
\
+ __builtin_types_compatible_p(typeof(expr), volatile signed char) ||
\
+ __builtin_types_compatible_p(typeof(expr), const volatile signed
char), \
+ (signed char)1,
\
+ __builtin_choose_expr(
\
+ __builtin_types_compatible_p(typeof(expr), unsigned char) ||
\
+ __builtin_types_compatible_p(typeof(expr), const unsigned char) ||
\
+ __builtin_types_compatible_p(typeof(expr), volatile unsigned char) ||
\
+ __builtin_types_compatible_p(typeof(expr), const volatile unsigned
char), \
+ (unsigned char)1,
\
+ __builtin_choose_expr(
\
+ __builtin_types_compatible_p(typeof(expr), signed short) ||
\
+ __builtin_types_compatible_p(typeof(expr), const signed short) ||
\
+ __builtin_types_compatible_p(typeof(expr), volatile signed short) ||
\
+ __builtin_types_compatible_p(typeof(expr), const volatile signed
short), \
+ (signed short)1,
\
+ __builtin_choose_expr(
\
+ __builtin_types_compatible_p(typeof(expr), unsigned short) ||
\
+ __builtin_types_compatible_p(typeof(expr), const unsigned short) ||
\
+ __builtin_types_compatible_p(typeof(expr), volatile unsigned short) ||
\
+ __builtin_types_compatible_p(typeof(expr), const volatile unsigned
short), \
+ (unsigned short)1,
\
+ (expr)+0))))))
+#endif
