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include: move typeof_strip_qual to compiler.h, use it in QAPI_LIST_LENGTH()

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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-flwu@google.com/

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Tested-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2024-06-25 13:12:20 +02:00
parent 7246c4cc47
commit eb350d1d01
3 changed files with 47 additions and 43 deletions
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46
include/qemu/compiler.h
View file

@ -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
#endif /* COMPILER_H */