On Thu, 2018-10-11 at 18:02 +0200, Arnd Bergmann wrote: > On 10/10/18, Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > > Hello, > > I noticed that compiling with > > CONFIG_TCG_TPM=y > > CONFIG_HW_RANDOM_TPM=y > > and Clang produced the warning: > > > > CC security/keys/trusted.o > > 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: > > > > The parameter parmN is the identifier of the rightmost parameter in > > the variable parameter list in the function definition (the one > > just before the ...). If the parameter parmN is declared with ... > > or with a type that is not compatible with the type that results > > after application of the default argument promotions, the behavior > > is undefined. > > > > So if I understand my C promotion/conversion rules correctly, > > unsigned char would be promoted to int? > > > > We had a few ideas for possible fixes in: > > https://github.com/ClangBuiltLinux/linux/issues/41 > > I arrived at a similar patch as the one cited there, but it broke > again after an 'extern' declaration was added in > include/keys/trusted.h, so that has to be patched as well now They look either over complicated or potentially problematic. since this is an internal API and a char * is always legal, what's wrong with simply swapping h2 and h3? James
