On Wed 2022-03-02 10:58:49, John Ogness wrote: > On 2022-03-01, Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > >> > lib/vsprintf.c: In function 'va_format': > >> > lib/vsprintf.c:1759:9: warning: function 'va_format' might be a candidate for 'gnu_printf' format attribute [-Wsuggest-attribute=format] > >> > 1759 | buf += vsnprintf(buf, end > buf ? end - buf : 0, va_fmt->fmt, va); > >> > | ^~~ > >> > >> I wonder what this means. > > > > It means the compiler thinks we might want to add: > > > > __attribute__((format(gnu_printf, x, y))) to the function declaration so it > > can type-check the arguments. > > > > 'format (ARCHETYPE, STRING-INDEX, FIRST-TO-CHECK)' > > The 'format' attribute specifies that a function takes 'printf', > > 'scanf', 'strftime' or 'strfmon' style arguments that should be > > type-checked against a format string. For example, the > > declaration: > > > > extern int > > my_printf (void *my_object, const char *my_format, ...) > > __attribute__ ((format (printf, 2, 3))); > > > > causes the compiler to check the arguments in calls to 'my_printf' > > for consistency with the 'printf' style format string argument > > 'my_format'. > > > > > > I haven't looked into this at all and have no idea if we should. > > AFAICT it is not possible to use the gnu_printf format attribute for > this because the va_list to check is a field within the passed in struct > pointer @va_fmt. My understanding is that it can be handled by passing '0' as the FIRST-TO-CHECK parameter: <paste> format (archetype, string-index, first-to-check) The format attribute specifies that a function takes printf, scanf, strftime or strfmon style arguments that should be type-checked against a format string. For example, the declaration: [...] "For functions where the arguments are not available to be checked (such as vprintf), specify the third parameter as zero." <paste> , cut&pasted from https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#Common-Function-Attributes Well, this particular function va_format() is never used with open-coded @arg parameter. It always just passes @arg from the caller. So that the check is not important. Best Regards, Petr
