Re: struct mctelem_cookie missing definition

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 12 Feb 2025, Stefano Stabellini wrote:
> On Thu, 13 Feb 2025, Andrew Cooper wrote:
> > On 13/02/2025 1:25 am, Stefano Stabellini wrote:
> > > Hi all,
> > >
> > > I am looking through the few remaining MISRA violations that we have
> > > left.  One of them is R11.2:
> > >
> > > https://saas.eclairit.com:3787/fs/var/local/eclair/xen-project.ecdf/xen-project/hardware/xen/ECLAIR_normal/staging/X86_64/9118578464/PROJECT.ecd;/by_service/MC3A2.R11.2.html#{%22select%22:true,%22selection%22:{%22hiddenAreaKinds%22:[],%22hiddenSubareaKinds%22:[],%22show%22:false,%22selector%22:{%22enabled%22:true,%22negated%22:true,%22kind%22:0,%22domain%22:%22kind%22,%22inputs%22:[{%22enabled%22:true,%22text%22:%22violation%22}]}}}
> > >
> > > Specifically, mctelem_cookie_t is a pointer to incomplete type and
> > > therefore COOKIE2MCTE triggers a "conversion between a pointer to an
> > > incomplete type and any other type".
> > >
> > > mctelem_cookie_t is defined as:
> > >
> > > typedef struct mctelem_cookie *mctelem_cookie_t;
> > >
> > > I am looking through the code and I genuinely cannot find the definition
> > > of struct mctelem_cookie.
> > >
> > > If mctelem_cookie_t is only used as a pointer, wouldn't it make more
> > > sense to do:
> > >
> > > typedef struct mctelem_ent *mctelem_cookie_t;
> > >
> > > ?
> > >
> > > What am I missing?
> > 
> > Nothing.  Or perhaps the twisted thinking of the original author.
> > 
> > It is genuinely a pointer type (== known size) which you can't deference
> > (because there is no definition), and can only operate on by casting to
> > an integer.  Except the code also requires it to be a uint64_t which is
> > why there's some fun disabling of relevant hypercalls for compat guests.
> > 
> > If someone could find the time to file it in /dev/null and replace it
> > with literally anything else, I'd be very thankful.
> 
> Are you OK with typedefing mctelem_cookie_t to uint64_t instead?

I confirm that the following resolves the MISRA violations

diff --git a/xen/arch/x86/cpu/mcheck/mctelem.h 
b/xen/arch/x86/cpu/mcheck/mctelem.h
index f4c5ff848d..2ccd490e5d 100644
--- a/xen/arch/x86/cpu/mcheck/mctelem.h
+++ b/xen/arch/x86/cpu/mcheck/mctelem.h
@@ -52,7 +52,7 @@
  * the element from the processing list.
  */
 
-typedef struct mctelem_cookie *mctelem_cookie_t;
+typedef uint64_t *mctelem_cookie_t;
 
 typedef enum mctelem_class {
     MC_URGENT,