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From: Borislav Petkov <bp@alien8.de>
To: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Nathan Chancellor <natechancellor@gmail.com>,
	Arnd Bergmann <arnd@kernel.org>, Ard Biesheuvel <ardb@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	x86@kernel.org, Nick Desaulniers <ndesaulniers@google.com>,
	Arnd Bergmann <arnd@arndb.de>, Darren Hart <dvhart@infradead.org>,
	Andy Shevchenko <andy@infradead.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	linux-efi@vger.kernel.org, platform-driver-x86@vger.kernel.org,
	linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com
Subject: Re: [PATCH] x86: efi: avoid BUILD_BUG_ON() for non-constant p4d_index
Date: Fri, 15 Jan 2021 20:18:33 +0100	[thread overview]
Message-ID: <20210115191833.GF9138@zn.tnic> (raw)
In-Reply-To: <YAHo3ZEMu+6mESZA@rani.riverdale.lan>

On Fri, Jan 15, 2021 at 02:11:25PM -0500, Arvind Sankar wrote:
> That's how build-time assertions work: they are _supposed_ to be
> optimized away completely when the assertion is true. If they're
> _not_ optimized away, the build will fail.

Yah, that I know, thanks.

If gcc really inlines p4d_index() and does a lot more aggressive
optimization to determine that the condition is false and thus optimize
everything away (and clang doesn't), then that would explain the
observation.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

  reply	other threads:[~2021-01-15 19:19 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-07 22:34 [PATCH] x86: efi: avoid BUILD_BUG_ON() for non-constant p4d_index Arnd Bergmann
2021-01-07 22:42 ` Nathan Chancellor
2021-01-13 17:51 ` Ard Biesheuvel
2021-01-15 18:23 ` Borislav Petkov
2021-01-15 18:32   ` Nathan Chancellor
2021-01-15 19:07     ` Borislav Petkov
2021-01-15 19:11       ` Arvind Sankar
2021-01-15 19:18         ` Borislav Petkov [this message]
2021-01-15 19:54           ` Arnd Bergmann
2021-01-15 20:12             ` Arvind Sankar
2021-01-15 20:32               ` Arvind Sankar
2021-01-15 19:07 ` Arvind Sankar
2021-01-15 20:27   ` Arvind Sankar
2021-01-16 16:34     ` Ard Biesheuvel
2021-01-18 20:24       ` Borislav Petkov
2021-01-18 21:42         ` Arvind Sankar
2021-01-20  9:33           ` Ard Biesheuvel
2021-01-20 11:44             ` Borislav Petkov
2021-02-03 18:51             ` Nathan Chancellor
2021-02-03 20:29               ` Ard Biesheuvel
2021-02-04 10:51                 ` Borislav Petkov
2021-02-04 10:59                   ` Ard Biesheuvel
2021-02-04 19:16                   ` Nathan Chancellor
2021-02-04 21:43                   ` Arvind Sankar
2021-02-04 22:13                     ` Borislav Petkov
2021-02-05  0:08                       ` Arvind Sankar
2021-02-05 11:39                         ` [PATCH] x86/efi: Remove EFI PGD build time checks Borislav Petkov
2021-02-05 11:57                           ` Ard Biesheuvel
2021-02-05 18:14                           ` Nick Desaulniers
2021-02-05 18:56                           ` Nathan Chancellor
2021-02-05 10:34               ` [PATCH] x86: efi: avoid BUILD_BUG_ON() for non-constant p4d_index Borislav Petkov
2021-02-05 18:27                 ` Nick Desaulniers
2021-02-05 18:31                   ` Nathan Chancellor
2021-01-20 11:26           ` Kirill A. Shutemov
2021-01-20 11:06   ` Kirill A. Shutemov
2021-02-06 12:56 ` [tip: x86/urgent] x86/efi: Remove EFI PGD build time checks tip-bot2 for Borislav Petkov

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