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use _Static_assert in QEMU_BUILD_BUG_ON

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QEMU_BUILD_BUG_ON should use C11's _Static_assert, if the compiler supports it,
to provide more readable messages on failure.

We check for _Static_assert in configure, and set CONFIG_STATIC_ASSERT
accordingly. QEMU_BUILD_BUG_ON invokes _Static_assert if CONFIG_STATIC_ASSERT
is defined, and reverts to the old way otherwise.

That way, systems without C11 conforming compiler will still have the old
messages, as verified by intentionally breaking the configure check.

the following example output was generated by inverting the condition in
QEMU_BUILD_BUG_ON:

without _Static_assert:

> In file included from /qemu/include/qemu/osdep.h:36:0,
> from /qemu/qga/commands.c:13:
> /qemu/qga/commands.c: In function ‘qmp_guest_exec_status’:
> /qemu/include/qemu/compiler.h:89:12: error: negative width in bit-field ‘<anonymous>’
> struct { \
> ^
> /qemu/include/qemu/compiler.h:96:38: note: in expansion of macro QEMU_BUILD_BUG_ON_STRUCT’
> #define QEMU_BUILD_BUG_ON(x) typedef QEMU_BUILD_BUG_ON_STRUCT(x) \
> ^~~~~~~~~~~~~~~~~~~~~~~~
> /qemu/include/qemu/atomic.h:146:5: note: in expansion of macro ‘QEMU_BUILD_BUG_ON’
> QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
> ^~~~~~~~~~~~~~~~~
> /qemu/include/qemu/atomic.h:417:5: note: in expansion of macro ‘atomic_load_acquire’
> atomic_load_acquire(ptr)
> ^~~~~~~~~~~~~~~~~~~
> /qemu/qga/commands.c:160:21: note: in expansion of macro ‘atomic_mb_read’
> bool finished = atomic_mb_read(&gei->finished);
> ^~~~~~~~~~~~~~

with _Static_assert:

> In file included from /qemu/include/qemu/osdep.h:36:0,
> from /qemu/qga/commands.c:13:
> /qemu/qga/commands.c: In function ‘qmp_guest_exec_status’:
> /qemu/include/qemu/compiler.h:94:30: error: static assertion failed: "not expecting: sizeof(*&gei->finished) > sizeof(void *)"
> #define QEMU_BUILD_BUG_ON(x) _Static_assert((x), #x)
> ^
> /qemu/include/qemu/atomic.h:146:5: note: in expansion of macro ‘QEMU_BUILD_BUG_ON’
> QEMU_BUILD_BUG_ON(sizeof(*ptr) > sizeof(void *)); \
> ^~~~~~~~~~~~~~~~~
> /qemu/include/qemu/atomic.h:417:5: note: in expansion of macro ‘atomic_load_acquire’
> atomic_load_acquire(ptr)
> ^~~~~~~~~~~~~~~~~~~
> /qemu/qga/commands.c:160:21: note: in expansion of macro ‘atomic_mb_read’
> bool finished = atomic_mb_read(&gei->finished);
> ^~~~~~~~~~~~~~

Backports commit 49e00a18708e27c815828d9440d5c9300d19547c from qemu
This commit is contained in:
Andreas Grapentin 2018-03-20 10:41:11 -04:00 committed by Lioncash
parent 910d50be6b
commit 4f6ba5a2dc
No known key found for this signature in database
GPG key ID: 4E3C3CC1031BA9C7
2 changed files with 23 additions and 2 deletions
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17
qemu/configure vendored
View file

@ -1308,6 +1308,19 @@ if compile_prog "" "" ; then
posix_memalign=yes
fi
# check for _Static_assert()
have_static_assert=no
cat > $TMPC << EOF
_Static_assert(1, "success");
int main(void) {
return 0;
}
EOF
if compile_prog "" "" ; then
have_static_assert=yes
fi
##########################################
# End of CC checks
# After here, no more $cc or $ld runs
@ -1488,6 +1501,10 @@ if test "$vector16" = "yes" ; then
echo "CONFIG_VECTOR16=y" >> $config_host_mak
fi
if test "$have_static_assert" = "yes" ; then
echo "CONFIG_STATIC_ASSERT=y" >> $config_host_mak
fi
if test "$tcg_interpreter" = "yes"; then
QEMU_INCLUDES="-I\$(SRC_PATH)/tcg/tci $QEMU_INCLUDES"
elif test "$ARCH" = "sparc64" ; then

8
qemu/include/qemu/compiler.h
View file

@ -72,7 +72,9 @@ static union MSVC_FLOAT_HACK __NAN = {{0x00, 0x00, 0xC0, 0x7F}};
int:(x) ? -1 : 1; \
}
#ifdef __COUNTER__
#if defined(CONFIG_STATIC_ASSERT)
#define QEMU_BUILD_BUG_ON(x) _Static_assert(!(x), "not expecting: " #x)
#elif defined(__COUNTER__)
#define QEMU_BUILD_BUG_ON(x) typedef QEMU_BUILD_BUG_ON_STRUCT(x) \
glue(qemu_build_bug_on__, __COUNTER__) QEMU_UNUSED_VAR
#else
@ -188,7 +190,9 @@ static union MSVC_FLOAT_HACK __NAN = {{0x00, 0x00, 0xC0, 0x7F}};
int:(x) ? -1 : 1; \
}
#ifdef __COUNTER__
#if defined(CONFIG_STATIC_ASSERT)
#define QEMU_BUILD_BUG_ON(x) _Static_assert(!(x), "not expecting: " #x)
#elif defined(__COUNTER__)
#define QEMU_BUILD_BUG_ON(x) typedef QEMU_BUILD_BUG_ON_STRUCT(x) \
glue(qemu_build_bug_on__, __COUNTER__) QEMU_UNUSED_VAR
#else