Re: [XEN PATCH] xen/mem_access: address violations of MISRA C: 2012 Rule 8.4

[Julien Grall <julien@xxxxxxx>]

Hi,

On 03/05/2024 08:09, Alessandro Zucchelli wrote:
> On 2024-04-29 17:58, Jan Beulich wrote:
> > On 29.04.2024 17:45, Alessandro Zucchelli wrote:
> > > Change #ifdef CONFIG_MEM_ACCESS by OR-ing defined(CONFIG_ARM),
> > > allowing asm/mem_access.h to be included in all ARM build 
> > > configurations.
> > > This is to address the violation of MISRA C: 2012 Rule 8.4 which states:
> > > "A compatible declaration shall be visible when an object or function
> > > with external linkage is defined". Functions p2m_mem_access_check
> > > and p2m_mem_access_check_and_get_page when CONFIG_MEM_ACCESS is not
> > > defined in ARM builds don't have visible declarations in the file
> > > containing their definitions.
> > >
> > > Signed-off-by: Alessandro Zucchelli <alessandro.zucchelli@xxxxxxxxxxx>
> > > ---
> > >  xen/include/xen/mem_access.h | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/xen/include/xen/mem_access.h b/xen/include/xen/mem_access.h
> > > index 87d93b31f6..ec0630677d 100644
> > > --- a/xen/include/xen/mem_access.h
> > > +++ b/xen/include/xen/mem_access.h
> > > @@ -33,7 +33,7 @@
> > >   */
> > >  struct vm_event_st;
> > >
> > > -#ifdef CONFIG_MEM_ACCESS
> > > +#if defined(CONFIG_MEM_ACCESS) || defined(CONFIG_ARM)
> > >  #include <asm/mem_access.h>
> > >  #endif
> > This doesn't look quite right. If Arm supports mem-access, why would it
> > not set MEM_ACCESS=y? Whereas if it's only stubs that Arm supplies, then
> > those would better move here, thus eliminating the need for a per-arch
> > stub header (see what was e.g. done for numa.h). This way RISC-V and PPC
> > (and whatever is to come) would then be taken care of as well.
> ARM does support mem-access, so I don't think this is akin to the 
> changes done to handle numa.h.
> ARM also allows users to set MEM_ACCESS=n (e.g. 
> xen/arch/arm/configs/tiny64_defconfig) and builds just fine; however, 
> the implementation file mem_access.c is compiled unconditionally in 
> ARM's makefile, hence why the violation was spotted.
> This is a bit unusual, so I was also hoping to get some feedback from 
> mem-access maintainers as to why this discrepancy from x86 exists. I 
> probably should have also included some ARM maintainers as well, so I'm 
> going to loop them in now.
> An alternative option I think is to make the compilation of arm's 
> mem_access.c conditional on CONFIG_MEM_ACCESS (as for x86/mm and common).
I can't think of a reason to have mem_access.c unconditional compiled 
in. So I think it should be conditional like on x86.
Cheers,

--
Julien Grall