Re: [Xen-devel] [PATCH] x86/xen: Distribute switch variables for initialization

[Jürgen Groß <jgross@xxxxxxxx>]

On 20.02.20 07:23, Kees Cook wrote:
> Variables declared in a switch statement before any case statements
> cannot be automatically initialized with compiler instrumentation (as
> they are not part of any execution flow). With GCC's proposed automatic
> stack variable initialization feature, this triggers a warning (and they
> don't get initialized). Clang's automatic stack variable initialization
> (via CONFIG_INIT_STACK_ALL=y) doesn't throw a warning, but it also
> doesn't initialize such variables[1]. Note that these warnings (or silent
> skipping) happen before the dead-store elimination optimization phase,
> so even when the automatic initializations are later elided in favor of
> direct initializations, the warnings remain.
>
> To avoid these problems, move such variables into the "case" where
> they're used or lift them up into the main function body.
>
> arch/x86/xen/enlighten_pv.c: In function ‘xen_write_msr_safe’:
> arch/x86/xen/enlighten_pv.c:904:12: warning: statement will never be executed 
> [-Wswitch-unreachable]
>    904 |   unsigned which;
>        |            ^~~~~
>
> [1] https://bugs.llvm.org/show_bug.cgi?id=44916
>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>


Juergen

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