From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Arnd Bergmann <arnd@kernel.org>, Ard Biesheuvel <ardb@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, Nathan Chancellor <natechancellor@gmail.com>,
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: Wed, 20 Jan 2021 14:06:04 +0300 [thread overview]
Message-ID: <20210120110604.bms6yjoiluojj4x4@box> (raw)
In-Reply-To: <YAHoB4ODvxSqNhsq@rani.riverdale.lan>
On Fri, Jan 15, 2021 at 02:07:51PM -0500, Arvind Sankar wrote:
> On Thu, Jan 07, 2021 at 11:34:15PM +0100, Arnd Bergmann wrote:
> > From: Arnd Bergmann <arnd@arndb.de>
> >
> > When 5-level page tables are enabled, clang triggers a BUILD_BUG_ON():
> >
> > x86_64-linux-ld: arch/x86/platform/efi/efi_64.o: in function `efi_sync_low_kernel_mappings':
> > efi_64.c:(.text+0x22c): undefined reference to `__compiletime_assert_354'
> >
> > Use the same method as in commit c65e774fb3f6 ("x86/mm: Make PGDIR_SHIFT
> > and PTRS_PER_P4D variable") and change it to MAYBE_BUILD_BUG_ON(),
> > so it only triggers for constant input.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/256
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> > ---
> > arch/x86/platform/efi/efi_64.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> > index e1e8d4e3a213..62bb1616b4a5 100644
> > --- a/arch/x86/platform/efi/efi_64.c
> > +++ b/arch/x86/platform/efi/efi_64.c
> > @@ -137,8 +137,8 @@ void efi_sync_low_kernel_mappings(void)
> > * As with PGDs, we share all P4D entries apart from the one entry
> > * that covers the EFI runtime mapping space.
> > */
> > - BUILD_BUG_ON(p4d_index(EFI_VA_END) != p4d_index(MODULES_END));
> > - BUILD_BUG_ON((EFI_VA_START & P4D_MASK) != (EFI_VA_END & P4D_MASK));
> > + MAYBE_BUILD_BUG_ON(p4d_index(EFI_VA_END) != p4d_index(MODULES_END));
> > + MAYBE_BUILD_BUG_ON((EFI_VA_START & P4D_MASK) != (EFI_VA_END & P4D_MASK));
> >
> > pgd_efi = efi_pgd + pgd_index(EFI_VA_END);
> > pgd_k = pgd_offset_k(EFI_VA_END);
> > --
> > 2.29.2
> >
>
> I think this needs more explanation as to why clang is triggering this.
> The issue mentions clang not inline p4d_index(), and I guess not
> performing inter-procedural analysis either?
>
> For the second assertion there, everything is always constant AFAICT:
> EFI_VA_START, EFI_VA_END and P4D_MASK are all constants regardless of
> CONFIG_5LEVEL.
Back in the days BUILD_BUG_ON() false-triggered on GCC-4.8 as well.
--
Kirill A. Shutemov
next prev parent reply other threads:[~2021-01-20 11:51 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
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 [this message]
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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