Re: [Qemu-devel] [PATCH for-3.1? 2/3] migration: fix stringop-truncation warning

[Eric Blake <eblake@redhat.com>]

On 11/20/18 9:27 AM, Marc-André Lureau wrote:
> Adding an assert is enough to silence GCC.
> 
> ~/src/qemu/migration/global_state.c: In function 'global_state_store_running':
> ~/src/qemu/migration/global_state.c:45:5: error: 'strncpy' specified bound 100 equals destination size [-Werror=stringop-truncation]
>       strncpy((char *)global_state.runstate,
>       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>              state, sizeof(global_state.runstate));
>              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> cc1: all warnings being treated as errors
> 
> (alternatively, we could hard-code "running")
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>   migration/global_state.c | 1 +
>   1 file changed, 1 insertion(+)

Reviewed-by: Eric Blake <eblake@redhat.com>

I think this is safe for 3.1, but I know the migration code is 
particularly wary of assert()s, even when they are non-triggerable (a 
100-byte buffer at global_state.runstate is big enough for ALL of the 
run states, not just RUN_STATE_RUNNING).

> 
> diff --git a/migration/global_state.c b/migration/global_state.c
> index 8e8ab5c51e..01805c567a 100644
> --- a/migration/global_state.c
> +++ b/migration/global_state.c
> @@ -42,6 +42,7 @@ int global_state_store(void)
>   void global_state_store_running(void)
>   {
>       const char *state = RunState_str(RUN_STATE_RUNNING);
> +    assert(strlen(state) < sizeof(global_state.runstate));
>       strncpy((char *)global_state.runstate,
>              state, sizeof(global_state.runstate));
>   }
> 

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org