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Message-ID: <517E9405.8030509@zytor.com> Date: Mon, 29 Apr 2013 08:38:45 -0700 From: "H. Peter Anvin" <hpa@...or.com> To: Borislav Petkov <bp@...en8.de> CC: X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>, Borislav Petkov <bp@...e.de> Subject: Re: [PATCH 2/3] x86: Sanity-check static_cpu_has usage On 04/29/2013 07:04 AM, Borislav Petkov wrote: > From: Borislav Petkov <bp@...e.de> > > static_cpu_has may be used only after alternatives have run. Before that > it always returns false if constant folding with __builtin_constant_p() > doesn't happen. And you don't want that. > > This patch is the result of me debugging an issue where I overzealously > put static_cpu_has in code which executed before alternatives have run > and had to spend some time with scratching head and cursing at the > monitor. > > So add a jump to a warning which screams loudly when we use this > function too early. The alternatives patch that check away in > conjunction with patching the rest of the kernel image. > > This first JMP the compiler then issues should always be a two-byte JMP > because its relative offset fits in a byte. This gets replaced by only a > two-byte NOP => less instruction cache bloat. > I still would prefer this to be an option. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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