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Re: [PATCH 1/3] xen/keyhandler: add missing noreturn attribute
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
- Date: Thu, 05 Jun 2025 14:22:02 +0200
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- Cc: victorm.lira@xxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Federico Serafini <federico.serafini@xxxxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 05 Jun 2025 12:22:12 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 2025-06-05 09:17, Jan Beulich wrote:
On 05.06.2025 01:49, victorm.lira@xxxxxxx wrote:
From: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
Function `reboot_machine' does not return, but lacks the `noreturn'
attribute,
therefore causing a violation of MISRA C Rule 2.1: "A project shall
not contain
unreachable code".
Is this (uniformly) true? Looking at ...
--- a/xen/common/keyhandler.c
+++ b/xen/common/keyhandler.c
@@ -251,7 +251,7 @@ static void cf_check dump_hwdom_registers(unsigned
char key)
}
}
-static void cf_check reboot_machine(unsigned char key, bool unused)
+static void noreturn cf_check reboot_machine(unsigned char key, bool
unused)
{
printk("'%c' pressed -> rebooting machine\n", key);
machine_restart(0);
... generated code here, I can see that the compiler is perfectly able
to
leverage the noreturn that machine_restart() has, resulting in no
unreachable code to be generated. That is - neither in source nor in
binary there is any unreachable code. Therefore I'm having a hard time
seeing what the violation is here.
That said, I certainly don't mind the addition of the (seemingly)
missing
attribute. Otoh I wonder whether an attribute the removal of which has
no
effect wouldn't count as "dead code" or alike, violating some other
rule.
Inlining does not play a role in this case. Here reboot_machine() is
marked as a violation because machine_restart() is noreturn and there is
no other path upon which reboot_machine() may return, hence any function
calling reboot_machine() could have portions that are inadvertently
unreachable (as in never executed due to divergence) by not having the
annotation. That said, in such trivial cases compilers are typically
able to derive the property automatically, but they are not obliged to
and, more importantly, the behavior may even differ with the same
compiler using different optimization levels.
--
Nicola Vetrini, B.Sc.
Software Engineer
BUGSENG (https://bugseng.com)
LinkedIn: https://www.linkedin.com/in/nicola-vetrini-a42471253
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