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Re: [PATCH for-4.14 3/3] xen/x86: atomic: Don't allow to write atomically in a pointer to const

Hi Jan,

On 04/05/2020 11:47, Jan Beulich wrote:
On 02.05.2020 18:07, Julien Grall wrote:
From: Julien Grall <jgrall@xxxxxxxxxx>

At the moment, write_atomic() will happily write to a pointer to const.
While there are no use in Xen, it would be best to catch them at
compilation time.

Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
albeit ...

--- a/xen/include/asm-x86/atomic.h
+++ b/xen/include/asm-x86/atomic.h
@@ -63,6 +63,8 @@ void __bad_atomic_size(void);
#define write_atomic(p, x) ({ \
      typeof(*(p)) __x = (x);                               \
+    /* Check that the pointer is not const */             \
+    void *__maybe_unused p_ = &__x;                       \

... along the lines of the similar case with guest handles I'd
like to suggest for the comment to be more precise: It's not
the pointer's const-ness you're after, but the pointed to
object's. Maybe "Check that the pointer is not to a const
type" or even just "Check that the pointer is not to const"?

I am happy with "Check that the pointer is not to a const type".


Julien Grall



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