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Re: [XEN PATCH 1/3] EFI: address violations of MISRA C Rule 13.6



On 2024-09-11 16:10, Jan Beulich wrote:
On 11.09.2024 15:16, Marek Marczykowski-Górecki wrote:
On Wed, Sep 11, 2024 at 02:50:03PM +0200, Jan Beulich wrote:
On 10.09.2024 21:06, Federico Serafini wrote:
Refactor the code to improve readability

I question this aspect. I'm not the maintainer of this code anymore, so
my view probably doesn't matter much here.

and address violations of
MISRA C:2012 Rule 13.6 ("The operand of the `sizeof' operator shall
not contain any expression which has potential side effect").

Where's the potential side effect? Since you move ...

--- a/xen/common/efi/runtime.c
+++ b/xen/common/efi/runtime.c
@@ -250,14 +250,20 @@ int efi_get_info(uint32_t idx, union xenpf_efi_info *info)
         info->cfg.addr = __pa(efi_ct);
         info->cfg.nent = efi_num_ct;
         break;
+
     case XEN_FW_EFI_VENDOR:
+    {
+        XEN_GUEST_HANDLE_PARAM(CHAR16) vendor_name =
+            guest_handle_cast(info->vendor.name, CHAR16);

.. this out, it must be the one. I've looked at it, yet I can't spot
anything:

#define guest_handle_cast(hnd, type) ({         \
    type *_x = (hnd).p;                         \
    (XEN_GUEST_HANDLE_PARAM(type)) { _x };      \
})

As a rule of thumb, when things aren't obvious, please call out the
specific aspect / property in descriptions of such patches.

I guess it's because guest_handle_cast() is a macro, yet it's lowercase
so looks like a function?

If Eclair didn't look at the macro-expanded code, it wouldn't even see
the sizeof(). Hence I don't expect the thing to be mistaken for a function
call.


Looking at the fully preprocessed code [1], there is an assignment to CHAR *_x inside a sizeof(), therefore compat_handle_cast is triggering the violation when used in such a way to be inside the sizeof().

if ( !((!!((((get_cpu_info()->current_vcpu))->domain)->arch.paging.mode & ((1 << 4) << 10))) || ( __builtin_expect(!!(((n)) < (~0U / (sizeof(**(({ CHAR16 *_x = (__typeof__(**(info->vendor.name)._) *)(full_ptr_t)(info-> vendor.name).c; (__compat_handle_CHAR16) { (full_ptr_t)_x }; }))._)))),1) && ((unsigned long)((unsigned long)((void *)( full_ptr_t)(({ CHAR16 *_x = (__typeof__(**(info->vendor.name)._) *)(full_ptr_t)(info->vendor.name).c; ( __compat_handle_CHAR16) { (full_ptr_t)_x }; })).c) + ((0 + ((n)) * (sizeof(**(({ CHAR16 *_x = (__typeof__(**(info-> vendor.name)._) *)(full_ptr_t)(info->vendor.name).c; (__compat_handle_CHAR16) { (full_ptr_t)_x }; }))._))) ? (0 + ((n)) * (sizeof(**(({ CHAR16 *_x = (__typeof__(**(info->vendor.name)._) *)(full_ptr_t)(info->vendor.name).c; ( __compat_handle_CHAR16) { (full_ptr_t)_x }; }))._))) - 1 : 0)) < ((void)(((get_cpu_info()->current_vcpu))->domain), 0)))
) )

[1] https://saas.eclairit.com:3787/fs/var/local/eclair/XEN.ecdf/ECLAIR_normal/staging/X86_64-BUGSENG/latest/PROJECT.ecd;/by_service/MC3R1.R13.6.html#{"select":true,"selection":{"hiddenAreaKinds":[],"hiddenSubareaKinds":[],"show":false,"selector":{"enabled":true,"negated":true,"kind":0,"domain":"message","inputs":[{"enabled":true,"text":"^.*xen/common/efi/runtime\\.c:258\\.15-258\\.31: `sizeof' expression trait"}]}}}

Wasn't there some other MISRA rule about lowercase/uppercase for macro names?


There isn't one imposing this restriction (at least in MISRA C:2012, I haven't checked earlier editions).

I can't recall having run into one, but I also haven't memorized them all.

Jan

--
Nicola Vetrini, BSc
Software Engineer, BUGSENG srl (https://bugseng.com)



 


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