On Mon, Oct 15, 2018 at 2:26 AM David Laight <David.Laight@xxxxxxxxxx> wrote: > > From: ndesaulniers@xxxxxxxxxx > > Sent: 11 October 2018 21:31 > ... > > by swapping h2 and h3. > > > > security/keys/trusted.c:146:17: warning: passing an object that > > undergoes default > > argument promotion to 'va_start' has undefined behavior [-Wvarargs] > > va_start(argp, h3); > > ^ > > security/keys/trusted.c:126:37: note: parameter of type 'unsigned > > char' is declared here > > unsigned char *h2, unsigned char h3, ...) > > ^ > > Specifically, it seems that both the C90 (4.8.1.1) and C11 (7.16.1.4) > > standards explicitly call this out as undefined behavior: > > I guess that problems arise when all the arguments are stacked > and va_start/va_arg use naive pointer manipulation. > In that case &h3 might be 4n+3 aligned so va_arg() will access > misaligned stack locations. > > I doubt any modern compilers (where va_start and va_arg are builtins) > will get this 'wrong' even when all arguments are stacked. > > Seems clang is being over cautious. Yes; did you have feedback on the Denis' proposed fix, or another? > > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) -- Thanks, ~Nick Desaulniers
