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qemu/include/qemu/compiler.h
Zenghui Yu b59ea3640c compiler.h: Don't use compile-time assert when __NO_INLINE__ is defined 
Our robot reported the following compile-time warning while compiling
Qemu with -fno-inline cflags:

In function 'load_memop',
    inlined from 'load_helper' at /qemu/accel/tcg/cputlb.c:1578:20,
    inlined from 'full_ldub_mmu' at /qemu/accel/tcg/cputlb.c:1624:12:
/qemu/accel/tcg/cputlb.c:1502:9: error: call to 'qemu_build_not_reached' declared with attribute error: code path is reachable
         qemu_build_not_reached();
         ^~~~~~~~~~~~~~~~~~~~~~~~
    [...]

It looks like a false-positive because only (MO_UB ^ MO_BSWAP) will
hit the default case in load_memop() while need_swap (size > 1) has
already ensured that MO_UB is not involved.

So the thing is that compilers get confused by the -fno-inline and
just can't accurately evaluate memop_size(op) at compile time, and
then the qemu_build_not_reached() is wrongly triggered by (MO_UB ^
MO_BSWAP).  Let's carefully don't use the compile-time assert when
no functions will be inlined into their callers.

Reported-by: Euler Robot <euler.robot@huawei.com>
Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Message-Id: <20200205141545.180-1-yuzenghui@huawei.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
2020-02-28 10:58:41 -08:00

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/* compiler.h: macros to abstract away compiler specifics
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*/
#ifndef COMPILER_H
#define COMPILER_H
#if defined __clang_analyzer__ || defined __COVERITY__
#define QEMU_STATIC_ANALYSIS 1
#endif
/*----------------------------------------------------------------------------
| The macro QEMU_GNUC_PREREQ tests for minimum version of the GNU C compiler.
| The code is a copy of SOFTFLOAT_GNUC_PREREQ, see softfloat-macros.h.
*----------------------------------------------------------------------------*/
#if defined(__GNUC__) && defined(__GNUC_MINOR__)
# define QEMU_GNUC_PREREQ(maj, min) \
((__GNUC__ << 16) + __GNUC_MINOR__ >= ((maj) << 16) + (min))
#else
# define QEMU_GNUC_PREREQ(maj, min) 0
#endif
#define QEMU_NORETURN __attribute__ ((__noreturn__))
#define QEMU_WARN_UNUSED_RESULT __attribute__((warn_unused_result))
#define QEMU_SENTINEL __attribute__((sentinel))
#if defined(_WIN32) && (defined(__x86_64__) || defined(__i386__))
# define QEMU_PACKED __attribute__((gcc_struct, packed))
#else
# define QEMU_PACKED __attribute__((packed))
#endif
#define QEMU_ALIGNED(X) __attribute__((aligned(X)))
#ifndef glue
#define xglue(x, y) x ## y
#define glue(x, y) xglue(x, y)
#define stringify(s) tostring(s)
#define tostring(s) #s
#endif
#ifndef likely
#if __GNUC__ < 3
#define __builtin_expect(x, n) (x)
#endif
#define likely(x) __builtin_expect(!!(x), 1)
#define unlikely(x) __builtin_expect(!!(x), 0)
#endif
#ifndef container_of
#define container_of(ptr, type, member) ({ \
const typeof(((type *) 0)->member) *__mptr = (ptr); \
(type *) ((char *) __mptr - offsetof(type, member));})
#endif
#define sizeof_field(type, field) sizeof(((type *)0)->field)
/*
* Calculate the number of bytes up to and including the given 'field' of
* 'container'.
*/
#define endof(container, field) \
(offsetof(container, field) + sizeof_field(container, field))
/* Convert from a base type to a parent type, with compile time checking. */
#ifdef __GNUC__
#define DO_UPCAST(type, field, dev) ( __extension__ ( { \
char __attribute__((unused)) offset_must_be_zero[ \
-offsetof(type, field)]; \
container_of(dev, type, field);}))
#else
#define DO_UPCAST(type, field, dev) container_of(dev, type, field)
#endif
#define typeof_field(type, field) typeof(((type *)0)->field)
#define type_check(t1,t2) ((t1*)0 - (t2*)0)
#define QEMU_BUILD_BUG_ON_STRUCT(x) \
struct { \
int:(x) ? -1 : 1; \
}
/* QEMU_BUILD_BUG_MSG() emits the message given if _Static_assert is
* supported; otherwise, it will be omitted from the compiler error
* message (but as it remains present in the source code, it can still
* be useful when debugging). */
#if defined(CONFIG_STATIC_ASSERT)
#define QEMU_BUILD_BUG_MSG(x, msg) _Static_assert(!(x), msg)
#elif defined(__COUNTER__)
#define QEMU_BUILD_BUG_MSG(x, msg) typedef QEMU_BUILD_BUG_ON_STRUCT(x) \
glue(qemu_build_bug_on__, __COUNTER__) __attribute__((unused))
#else
#define QEMU_BUILD_BUG_MSG(x, msg)
#endif
#define QEMU_BUILD_BUG_ON(x) QEMU_BUILD_BUG_MSG(x, "not expecting: " #x)
#define QEMU_BUILD_BUG_ON_ZERO(x) (sizeof(QEMU_BUILD_BUG_ON_STRUCT(x)) - \
sizeof(QEMU_BUILD_BUG_ON_STRUCT(x)))
#if defined __GNUC__
# if !QEMU_GNUC_PREREQ(4, 4)
/* gcc versions before 4.4.x don't support gnu_printf, so use printf. */
# define GCC_FMT_ATTR(n, m) __attribute__((format(printf, n, m)))
# else
/* Use gnu_printf when supported (qemu uses standard format strings). */
# define GCC_FMT_ATTR(n, m) __attribute__((format(gnu_printf, n, m)))
# if defined(_WIN32)
/* Map __printf__ to __gnu_printf__ because we want standard format strings
* even when MinGW or GLib include files use __printf__. */
# define __printf__ __gnu_printf__
# endif
# endif
#else
#define GCC_FMT_ATTR(n, m)
#endif
#ifndef __has_warning
#define __has_warning(x) 0 /* compatibility with non-clang compilers */
#endif
#ifndef __has_feature
#define __has_feature(x) 0 /* compatibility with non-clang compilers */
#endif
#ifndef __has_builtin
#define __has_builtin(x) 0 /* compatibility with non-clang compilers */
#endif
#if __has_builtin(__builtin_assume_aligned) || !defined(__clang__)
#define HAS_ASSUME_ALIGNED
#endif
#ifndef __has_attribute
#define __has_attribute(x) 0 /* compatibility with older GCC */
#endif
/*
* GCC doesn't provide __has_attribute() until GCC 5, but we know all the GCC
* versions we support have the "flatten" attribute. Clang may not have the
* "flatten" attribute but always has __has_attribute() to check for it.
*/
#if __has_attribute(flatten) || !defined(__clang__)
# define QEMU_FLATTEN __attribute__((flatten))
#else
# define QEMU_FLATTEN
#endif
/*
* If __attribute__((error)) is present, use it to produce an error at
* compile time. Otherwise, one must wait for the linker to diagnose
* the missing symbol.
*/
#if __has_attribute(error)
# define QEMU_ERROR(X) __attribute__((error(X)))
#else
# define QEMU_ERROR(X)
#endif
/*
* The nonstring variable attribute specifies that an object or member
* declaration with type array of char or pointer to char is intended
* to store character arrays that do not necessarily contain a terminating
* NUL character. This is useful in detecting uses of such arrays or pointers
* with functions that expect NUL-terminated strings, and to avoid warnings
* when such an array or pointer is used as an argument to a bounded string
* manipulation function such as strncpy.
*/
#if __has_attribute(nonstring)
# define QEMU_NONSTRING __attribute__((nonstring))
#else
# define QEMU_NONSTRING
#endif
/*
* Forced inlining may be desired to encourage constant propagation
* of function parameters. However, it can also make debugging harder,
* so disable it for a non-optimizing build.
*/
#if defined(__OPTIMIZE__)
#define QEMU_ALWAYS_INLINE __attribute__((always_inline))
#else
#define QEMU_ALWAYS_INLINE
#endif
/* Implement C11 _Generic via GCC builtins. Example:
*
* QEMU_GENERIC(x, (float, sinf), (long double, sinl), sin) (x)
*
* The first argument is the discriminator. The last is the default value.
* The middle ones are tuples in "(type, expansion)" format.
*/
/* First, find out the number of generic cases. */
#define QEMU_GENERIC(x, ...) \
QEMU_GENERIC_(typeof(x), __VA_ARGS__, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0)
/* There will be extra arguments, but they are not used. */
#define QEMU_GENERIC_(x, a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, count, ...) \
QEMU_GENERIC##count(x, a0, a1, a2, a3, a4, a5, a6, a7, a8, a9)
/* Two more helper macros, this time to extract items from a parenthesized
* list.
*/
#define QEMU_FIRST_(a, b) a
#define QEMU_SECOND_(a, b) b
/* ... and a final one for the common part of the "recursion". */
#define QEMU_GENERIC_IF(x, type_then, else_) \
__builtin_choose_expr(__builtin_types_compatible_p(x, \
QEMU_FIRST_ type_then), \
QEMU_SECOND_ type_then, else_)
/* CPP poor man's "recursion". */
#define QEMU_GENERIC1(x, a0, ...) (a0)
#define QEMU_GENERIC2(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC1(x, __VA_ARGS__))
#define QEMU_GENERIC3(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC2(x, __VA_ARGS__))
#define QEMU_GENERIC4(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC3(x, __VA_ARGS__))
#define QEMU_GENERIC5(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC4(x, __VA_ARGS__))
#define QEMU_GENERIC6(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC5(x, __VA_ARGS__))
#define QEMU_GENERIC7(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC6(x, __VA_ARGS__))
#define QEMU_GENERIC8(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC7(x, __VA_ARGS__))
#define QEMU_GENERIC9(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC8(x, __VA_ARGS__))
#define QEMU_GENERIC10(x, a0, ...) QEMU_GENERIC_IF(x, a0, QEMU_GENERIC9(x, __VA_ARGS__))
/**
* qemu_build_not_reached()
*
* The compiler, during optimization, is expected to prove that a call
* to this function cannot be reached and remove it. If the compiler
* supports QEMU_ERROR, this will be reported at compile time; otherwise
* this will be reported at link time due to the missing symbol.
*/
#if defined(__OPTIMIZE__) && !defined(__NO_INLINE__)
extern void QEMU_NORETURN QEMU_ERROR("code path is reachable")
qemu_build_not_reached(void);
#else
#define qemu_build_not_reached() g_assert_not_reached()
#endif
#endif /* COMPILER_H */
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