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SubjectRe: undefined behavior (-Wvarargs) in security/keys/trusted.c#TSS_authhmac()
On 10/10/18, Nick Desaulniers <> wrote:
> Hello,
> I noticed that compiling with
> 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 ( and C11 (
> 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:

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.


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