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Subject[PATCH v3 1/3] compiler_types.h: make __builtin_types_compatible_p() noop for Sparse
Date
When I tried to delete BUILD_BUG_ON stubs for sparse, the kbuild test
robot reported lots of Sparse warnings from container_of(), which
seem false positive.

The following checker in container_of() seems to be causing something
strange for Sparse.

BUILD_BUG_ON_MSG(!__same_type(*(ptr), ((type *)0)->member) && \
!__same_type(*(ptr), void), \
"pointer type mismatch in container_of()"); \

I narrowed down the problem into the following test code:

--------------------(test_code.c begin)--------------------
struct foo {
int (*callback)(void);
};

void assert(int);

static inline struct foo *get_foo(void)
{
assert(__builtin_types_compatible_p(void, void));

return (struct foo *)0;
}

int test(void);
int test(void)
{
return get_foo()->callback();
}
---------------------(test_code.c end)---------------------

Of course, GCC (and Clang as well) can compile it:

$ gcc -Wall -c -o test_code.o test_code.c

However, Sparse complains about this obviously correct code:

$ sparse test_code.c
test_code.c:9:45: warning: unknown expression (4 0)
test_code.c:9:51: warning: unknown expression (4 0)

Interstingly, just removing the 'inline' keyword in the test code
makes Sparse happy.

I concluded that Sparse cannot handle __builtin_types_compatible_p()
correctly. Make it no-op.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
---

Changes in v3:
- New patch

Changes in v2: None

include/linux/compiler_types.h | 1 +
1 file changed, 1 insertion(+)

diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
index 4a3f9c0..9e7da0b 100644
--- a/include/linux/compiler_types.h
+++ b/include/linux/compiler_types.h
@@ -23,6 +23,7 @@
extern void __chk_user_ptr(const volatile void __user *);
extern void __chk_io_ptr(const volatile void __iomem *);
# define ACCESS_PRIVATE(p, member) (*((typeof((p)->member) __force *) &(p)->member))
+# define __builtin_types_compatible_p(t1, t2) (1)
#else /* __CHECKER__ */
# ifdef STRUCTLEAK_PLUGIN
# define __user __attribute__((user))
--
2.7.4
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