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Re: [PATCH v2 4/4] tools/tests/x86_emulator: avoid passing NULL to memcpy
- To: Jan Beulich <jbeulich@xxxxxxxx>, Edwin Török <edwin.torok@xxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 3 Mar 2026 15:24:33 +0000
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 03 Mar 2026 15:24:49 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 03/03/2026 2:18 pm, Jan Beulich wrote:
> On 27.02.2026 11:58, Edwin Török wrote:
>> Fixes this `-fsanitize=undefined` error:
>> ```
>> test_x86_emulator.c:614:12: runtime error: null pointer passed as argument
>> 1, which is declared to never be null
>> /usr/include/string.h:44:28: note: nonnull attribute specified here
>> SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior
>> test_x86_emulator.c:614:12
>> ```
>>
>> Although this is more of a grey area: I don't see anything in the
>> standard that'd forbid calling `memset` with NULL and 0,
> There actually is. In the C99 spec clause 2 refers to section 7.1.4, where
> null
> pointer arguments are excluded. Imo for memcpy() etc exceptions should be made
> for the case where the count is also zero, but sadly nothing like that is
> there.
C23 does finally make NULL with a zero length be well defined behaviour
for memcpy() and friends, but it's going to be a long time before we can
rely on this properly.
GCC 15 gains __attribute__((nonzero_if_null)) too.
~Andrew
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