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



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



 


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