On Mon, Mar 9, 2015 at 7:14 AM, Denys Vlasenko <[email protected]> wrote:
> On Mon, Mar 9, 2015 at 2:43 PM, Andy Lutomirski <[email protected]> wrote:
>>> /* Offset from the sysenter stack to tss.sp0 */
>>> DEFINE(TSS_sysenter_sp0, offsetof(struct tss_struct, x86_tss.sp0) -
>>> - sizeof(struct tss_struct));
>>> + (offsetof(struct tss_struct, SYSENTER_stack_last_word) +
>>> 4));
>>
>> Is there no way to do this using sizeof to avoid having a "last_word" member.
>
> sizeof of a structure member? IIRC in C sizeof can't be used for that.
> You need to concoct a fictitious object, dereference its member
> and take sizeof of _that_.
>
> It would look horrible. Something like:
>
> offsetof(struct tss_struct, SYSENTER_stack) +
> sizeof(((struct tss_struct*)NULL)->SYSENTER_stack)
vfio.h has:
/**
* offsetofend(TYPE, MEMBER)
*
* @TYPE: The type of the structure
* @MEMBER: The member within the structure to get the end offset of
*
* Simple helper macro for dealing with variable sized structures passed
* from user space. This allows us to easily determine if the provided
* structure is sized to include various fields.
*/
#define offsetofend(TYPE, MEMBER) \
(offsetof(TYPE, MEMBER) + sizeof(((TYPE *)0)->MEMBER))
we could stick that in stdef.h and use it.
--Andy
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