On Sat, May 8, 2021 at 5:30 PM Andrew Morton akpm@linux-foundation.org wrote:
On Thu, 6 May 2021 14:20:25 -0700 Peter Collingbourne pcc@google.com wrote:
These tests deliberately access these arrays out of bounds, which will cause the dynamic local bounds checks inserted by CONFIG_UBSAN_LOCAL_BOUNDS to fail and panic the kernel. To avoid this problem, access the arrays via volatile pointers, which will prevent the compiler from being able to determine the array bounds.
Huh. Is this use of volatile the official way of suppressing the generation of the checking code or is it just something which happened to work? I'm wondering if this workaround should be formalized in some fashion (presumably a wrapper) rather than mysteriously and unexplainedly open-coding it like this.
I would consider it the official way in the sense that the compiler must assume that the pointer that it loads from the address of "array" has an arbitrary value due to the volatile qualifier, and the array bounds stuff follows from that. Actually I don't think the compiler is powerful enough yet to look through the store and load of "array", but if it were, I think that would be the right way to suppress the analysis.
Is the comment that I added in v2 not enough here?
Peter