Comment 15 for bug 1803872

On 12/18/18 11:51 AM, Philippe Mathieu-Daudé wrote:
> GCC 8 added a -Wstringop-truncation warning:
>
> The -Wstringop-truncation warning added in GCC 8.0 via r254630 for
> bug 81117 is specifically intended to highlight likely unintended
> uses of the strncpy function that truncate the terminating NUL
> character from the source string.
>
> This new warning leads to compilation failures:
>
> CC migration/global_state.o
> qemu/migration/global_state.c: In function 'global_state_store_running':
> 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));
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> make: *** [qemu/rules.mak:69: migration/global_state.o] Error 1
>
> Use the QEMU_NONSTRING attribute, since this array is intended to store
> character arrays that do not necessarily contain a terminating NUL.

> typedef struct {
> uint32_t size;
> - uint8_t runstate[100];
> + uint8_t runstate[100] QEMU_NONSTRING;

Since 100 bytes for runstate[] is larger than any string possible in our
current enum string values, could we instead add an assert that
strlen(state) < sizeof(global_state.runstate), and then use strpadcpy()
to make our intent obvious while still shutting up the compiler warning,
but without having to deal with the fallout of marking runstate as a
non-string?

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