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SubjectRe: [PATCH] KEYS: trusted: fix -Wvarags warning
On Mon, Oct 15, 2018 at 2:26 AM David Laight <David.Laight@aculab.com> wrote:
>
> From: ndesaulniers@google.com
> > 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

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