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From:   David Laight <David.Laight@ACULAB.COM>
To:     'Kees Cook' <keescook@chromium.org>
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Subject: RE: [PATCH v2 24/39] x86/cet/shstk: Add user-mode shadow stack
 support
Thread-Topic: [PATCH v2 24/39] x86/cet/shstk: Add user-mode shadow stack
 support
Thread-Index: AQHY12Njz3/HZpf9jkaO+WwIiUYgJ63+BXnggACK/wCAAT4eAA==
Date:   Wed, 5 Oct 2022 13:32:53 +0000
Message-ID: <b1d59744f54743a4a8131787580d181a@AcuMS.aculab.com>
References: <20220929222936.14584-1-rick.p.edgecombe@intel.com>
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 <202210031203.EB0DC0B7DD@keescook>
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From: Kees Cook
> Sent: 04 October 2022 20:32
...
> Oh, yes! I do this all the time with FORTIFY shenanigans. Right, so,
> instead of a macro, the "cannot be un-inlined" could be enforced with
> this (untested):
> 
> static __always_inline void set_clr_bits_msrl(u32 msr, u64 set, u64 clear)
> {
> 	u64 val, new_val;
> 
> 	BUILD_BUG_ON(!__builtin_constant_p(msr) ||
> 		     !__builtin_constant_p(set) ||
> 		     !__builtin_constant_p(clear));

You can reduce the amount of text the brain has to parse
by using:

	BUILD_BUG_ON(!__builtin_constant_p(msr + set + clear));

Just requires the brain to do a quick 'oh yes'...

	David

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