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. Arnd
