[Qemu-devel] [Bug 1803872] Re: [PATCH v3 4/5] migration: Use QEMU_NONSTRING for non NUL-terminated arrays

[Eric Blake <1803872@bugs.launchpad.net>]

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.
> 
> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>   migration/global_state.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)

Should this be squashed with 5/5?

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

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https://bugs.launchpad.net/bugs/1803872

Title:
  gcc 8.2 reports stringop-truncation when building qemu

Status in QEMU:
  New

Bug description:
  QEMU 3.0

  block/sheepdog.c: In function 'find_vdi_name':
  block/sheepdog.c:1239:5: error: 'strncpy' specified bound 256 equals destination size [-Werror=stringop-truncation]
       strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  If this is the intended behavior, please suppress the warning. For
  example:

  #pragma GCC diagnostic push
  #pragma GCC diagnostic ignored "-Wstringop-truncation"
      strncpy(buf + SD_MAX_VDI_LEN, tag, SD_MAX_VDI_TAG_LEN);
  #pragma GCC diagnostic pop

  This also happens on other sources, for example hw/acpi/core.c, so
  another option is to suppress it globally on CFLAGS (-Wno-stringop-
  truncation)

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