Re: [XEN PATCH] x86/mce: use offsetof to determine section offset

[Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>]

On 2026-01-14 21:40, Jason Andryuk wrote:
> On 2026-01-14 13:27, Nicola Vetrini wrote:
> > There is no reason to use pointer difference.
> > A violation of MISRA C Rule 18.2 ("Subtraction between pointers
> > shall only be applied to pointers that address elements of the
> > same array") is also resolved because the object to the subtraction
> > is applied is not an array.
> >
> > Signed-off-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
> > ---
> > Found while randomly browsing violations of the rule on the 
> > allcode-x86_64 scan.
> > ---
> >   xen/arch/x86/cpu/mcheck/mce-apei.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/xen/arch/x86/cpu/mcheck/mce-apei.c 
> > b/xen/arch/x86/cpu/mcheck/mce-apei.c
> > index b89502088243..21aabe2027d0 100644
> > --- a/xen/arch/x86/cpu/mcheck/mce-apei.c
> > +++ b/xen/arch/x86/cpu/mcheck/mce-apei.c
> > @@ -74,7 +74,8 @@ int apei_write_mce(struct mce *m)
> >         rcd.hdr.record_id = cper_next_record_id();
> >         rcd.hdr.flags = CPER_HW_ERROR_FLAGS_PREVERR;
> >   -     rcd.sec_hdr.section_offset = (void *)&rcd.mce - (void *)&rcd;
> > +       rcd.sec_hdr.section_offset = offsetof(struct cper_mce_record, mce) -
> > +                                    offsetof(struct cper_mce_record, hdr);
> "= offsetof(struct cper_mce_record, mce);" should be sufficient since 
> the offset of hdr is 0?
Yeah, makes sense. Given that the struct layout is coming from the UEFI 
spec it's not likely to change either.
> Regards,
> Jason
>
> >         rcd.sec_hdr.section_length = sizeof(rcd.mce);
> >         rcd.sec_hdr.revision = CPER_SEC_REV;
> >         /* fru_id and fru_text is invalid */
--
Nicola Vetrini, B.Sc.
Software Engineer
BUGSENG (https://bugseng.com)
LinkedIn: https://www.linkedin.com/in/nicola-vetrini-a42471253