Re: [PATCH-for-5.1?] qapi/error: Check format string argument in error_propagate_prepend()

[Markus Armbruster]

Philippe Mathieu-Daudé <philmd@redhat.com> writes:

> On 7/23/20 11:44 AM, Stefan Weil wrote:
>> Am 23.07.20 um 11:13 schrieb Philippe Mathieu-Daudé:
>> 
>>> error_propagate_prepend() "behaves like error_prepend()", and
>>> error_prepend() uses "formatting @fmt, ... like printf()".
>>> error_prepend() checks its format string argument, but
>>> error_propagate_prepend() does not. Fix that.
>>>
>>> This would have catched the invalid format introduced in commit
>>> b98e8d1230f:
>>>
>>>     CC      hw/sd/milkymist-memcard.o
>>>   hw/sd/milkymist-memcard.c: In function ‘milkymist_memcard_realize’:
>>>   hw/sd/milkymist-memcard.c:284:70: error: format ‘%s’ expects a matching 
>>> ‘char *’ argument [-Werror=format=]
>>>     284 |         error_propagate_prepend(errp, err, "failed to init SD 
>>> card: %s");
>>>         |                                                                   
>>>   ~^
>>>         |                                                                   
>>>    |
>>>         |                                                                   
>>>    char *
>>>
>>> Fixes: 4b5766488f ("Fix use of error_prepend() with &error_fatal, 
>>> &error_abort")
>>> Inspired-by: Stefan Weil <sw@weilnetz.de>
>>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>>> ---
>>>  include/qapi/error.h | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/include/qapi/error.h b/include/qapi/error.h
>>> index 7932594dce..eeeef1a34d 100644
>>> --- a/include/qapi/error.h
>>> +++ b/include/qapi/error.h
>>> @@ -381,6 +381,7 @@ void error_propagate(Error **dst_errp, Error 
>>> *local_err);
>>>   *     error_propagate(dst_errp, local_err);
>>>   * Please use ERRP_GUARD() and error_prepend() instead when possible.
>>>   */
>>> +GCC_FMT_ATTR(3, 4)
>>>  void error_propagate_prepend(Error **dst_errp, Error *local_err,
>>>                               const char *fmt, ...);

Wait!  You put the attribute in an unusual place.  We have it at the end
of the declaration elsewhere in this file.  Let's remain locally
consistent.

>> Reviewed-by: Stefan Weil <sw@weilnetz.de>
>> 
>> error_vprepend is one more candidate for GCC_FMT_ATTR. Maybe you can add
>> that, too.
>
> This one is different as it uses a va_list. Now I realize it is
> only called in util/error.c, and all its callers are guarded with
> GCC_FMT_ATTR. Maybe we can make it static to simplify... Markus?

Could use GCC_FMT_ATTR(2, 0).  Much less useful, but why not.

Perhaps a respin would be cleaner than me applying multiple tweaks.