[Qemu-devel] [Bug 1803872] Re: [PATCH v2 3/3] migration: Replace strncpy() by strpadcpy(pad='\0')

[elmarco]

On Tue, Dec 18, 2018 at 3:09 PM Philippe Mathieu-Daudé
<address@hidden> 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
>
> The runstate name doesn't require the strings to be NUL-terminated,
> therefore strncpy is the right function to use here.
>
> We could add a #pragma GCC diagnostic ignored "-Wstringop-truncation"
> around, disable the warning globally using -Wno-stringop-truncation,
> but since QEMU provides the strpadcpy() which does the same purpose,
> simply use it to avoid the annoying warning.
>
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>

Reviewed-by: Marc-André Lureau <address@hidden>

> ---
>  migration/global_state.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/migration/global_state.c b/migration/global_state.c
> index 8e8ab5c51e..c7e7618118 100644
> --- a/migration/global_state.c
> +++ b/migration/global_state.c
> @@ -42,8 +42,8 @@ int global_state_store(void)
>  void global_state_store_running(void)
>  {
>      const char *state = RunState_str(RUN_STATE_RUNNING);
> -    strncpy((char *)global_state.runstate,
> -           state, sizeof(global_state.runstate));
> +    strpadcpy((char *)global_state.runstate,
> +              sizeof(global_state.runstate), state, '\0');
>  }
>
>  bool global_state_received(void)
> --
> 2.17.2
>
>


-- 
Marc-André Lureau

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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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