From: Nick Desaulniers <ndesaulniers@google.com>
To: Nathan Chancellor <natechancellor@gmail.com>
Cc: "Masahiro Yamada" <masahiroy@kernel.org>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>,
"Borislav Petkov" <bp@alien8.de>,
"Michal Marek" <michal.lkml@markovi.net>,
"Linux Kbuild mailing list" <linux-kbuild@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
"Kees Cook" <keescook@chromium.org>,
"Tony Luck" <tony.luck@intel.com>,
"Dmitry Vyukov" <dvyukov@google.com>,
"Michael Ellerman" <mpe@ellerman.id.au>,
"Joe Perches" <joe@perches.com>,
"Joel Fernandes" <joel@joelfernandes.org>,
"Daniel Axtens" <dja@axtens.net>,
"Arvind Sankar" <nivedita@alum.mit.edu>,
"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
"Alexandru Ardelean" <alexandru.ardelean@analog.com>,
"Yury Norov" <yury.norov@gmail.com>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>,
"Ard Biesheuvel" <ardb@kernel.org>,
"Paul E . McKenney" <paulmck@kernel.org>,
"Daniel Kiper" <daniel.kiper@oracle.com>,
"Bruce Ashfield" <bruce.ashfield@gmail.com>,
"Marco Elver" <elver@google.com>,
"Vamshi K Sthambamkadi" <vamshi.k.sthambamkadi@gmail.com>,
"Andi Kleen" <ak@suse.de>,
"Linus Torvalds" <torvalds@linux-foundation.org>,
"Dávid Bolvanský" <david.bolvansky@gmail.com>,
"Eli Friedman" <efriedma@quicinc.com>
Subject: Re: [PATCH 2/4] Revert "lib/string.c: implement a basic bcmp"
Date: Tue, 18 Aug 2020 11:00:01 -0700 [thread overview]
Message-ID: <CAKwvOdm8iKUbfFP3a-2GjB1XQXp36Y9+B4kp2KX5iKbH-f0vDA@mail.gmail.com> (raw)
In-Reply-To: <20200818054428.GA2540870@ubuntu-n2-xlarge-x86>
On Mon, Aug 17, 2020 at 10:44 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> On Mon, Aug 17, 2020 at 03:02:10PM -0700, Nick Desaulniers wrote:
> > This reverts commit 5f074f3e192f10c9fade898b9b3b8812e3d83342.
> >
> > Use `-fno-builtin-bcmp` instead.
> >
> > The issue with using `-fno-builtin-*` flags was that they were not
> > retained during an LTO link with LLVM. This was fixed in clang-11 by
> > https://reviews.llvm.org/D71193
> > (0508c994f0b14144041f2cfd3ba9f9a80f03de08), which is also the minimum
> > supported version of clang for LTO.
> >
> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> > ---
> > Makefile | 1 +
> > include/linux/string.h | 3 ---
> > lib/string.c | 20 --------------------
> > 3 files changed, 1 insertion(+), 23 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index 211a1b6f6478..722ff5864275 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -964,6 +964,7 @@ endif
> > # to provide implementations of these routines, then prevent the compiler from
> > # emitting calls to what will be undefined symbols.
> > KBUILD_CFLAGS += -fno-builtin-stpcpy
> > +KBUILD_CFLAGS += -fno-builtin-bcmp
>
> I personally think that this hunk should be its own patch before this
> one then have this patch just be the revert, that way there is no
> regression across a bisect (if one were to ever occur) and so the revert
> is a straight 'git revert', rather than have something else mixed in
> that requires reading the actual changelog text.
>
> No objections if you disagree though.
That's a great idea. I considered it before sending, but I think it
would be interesting to divorce the KBUILD changes which can be picked
up quickly from the latter changes. Will send a V2.
>
> > # include additional Makefiles when needed
> > include-y := scripts/Makefile.extrawarn
> > diff --git a/include/linux/string.h b/include/linux/string.h
> > index b1f3894a0a3e..f3bdb74bc230 100644
> > --- a/include/linux/string.h
> > +++ b/include/linux/string.h
> > @@ -155,9 +155,6 @@ extern void * memscan(void *,int,__kernel_size_t);
> > #ifndef __HAVE_ARCH_MEMCMP
> > extern int memcmp(const void *,const void *,__kernel_size_t);
> > #endif
> > -#ifndef __HAVE_ARCH_BCMP
> > -extern int bcmp(const void *,const void *,__kernel_size_t);
> > -#endif
> > #ifndef __HAVE_ARCH_MEMCHR
> > extern void * memchr(const void *,int,__kernel_size_t);
> > #endif
> > diff --git a/lib/string.c b/lib/string.c
> > index 6012c385fb31..69328b8353e1 100644
> > --- a/lib/string.c
> > +++ b/lib/string.c
> > @@ -922,26 +922,6 @@ __visible int memcmp(const void *cs, const void *ct, size_t count)
> > EXPORT_SYMBOL(memcmp);
> > #endif
> >
> > -#ifndef __HAVE_ARCH_BCMP
> > -/**
> > - * bcmp - returns 0 if and only if the buffers have identical contents.
> > - * @a: pointer to first buffer.
> > - * @b: pointer to second buffer.
> > - * @len: size of buffers.
> > - *
> > - * The sign or magnitude of a non-zero return value has no particular
> > - * meaning, and architectures may implement their own more efficient bcmp(). So
> > - * while this particular implementation is a simple (tail) call to memcmp, do
> > - * not rely on anything but whether the return value is zero or non-zero.
> > - */
> > -#undef bcmp
> > -int bcmp(const void *a, const void *b, size_t len)
> > -{
> > - return memcmp(a, b, len);
> > -}
> > -EXPORT_SYMBOL(bcmp);
> > -#endif
> > -
> > #ifndef __HAVE_ARCH_MEMSCAN
> > /**
> > * memscan - Find a character in an area of memory.
> > --
> > 2.28.0.220.ged08abb693-goog
> >
>
> Cheers,
> Nathan
--
Thanks,
~Nick Desaulniers
next prev parent reply other threads:[~2020-08-18 18:00 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-17 22:02 [PATCH 0/4] -ffreestanding/-fno-builtin-* patches Nick Desaulniers
2020-08-17 22:02 ` [PATCH 1/4] Makefile: add -fno-builtin-stpcpy Nick Desaulniers
2020-08-17 22:31 ` H. Peter Anvin
2020-08-17 23:36 ` Nick Desaulniers
2020-08-18 19:21 ` Kees Cook
2020-08-18 7:10 ` Ard Biesheuvel
2020-08-18 7:25 ` Greg KH
2020-08-18 7:29 ` Ard Biesheuvel
2020-08-18 7:34 ` Greg KH
2020-08-18 19:23 ` Kees Cook
2020-08-17 22:02 ` [PATCH 2/4] Revert "lib/string.c: implement a basic bcmp" Nick Desaulniers
2020-08-18 5:44 ` Nathan Chancellor
2020-08-18 18:00 ` Nick Desaulniers [this message]
2020-08-18 19:24 ` Kees Cook
2020-08-17 22:02 ` [PATCH 3/4] x86/boot: use -fno-builtin-bcmp Nick Desaulniers
2020-08-18 19:24 ` Kees Cook
2020-08-17 22:02 ` [PATCH 4/4] x86: don't build CONFIG_X86_32 as -ffreestanding Nick Desaulniers
2020-08-18 19:24 ` Kees Cook
2021-01-07 0:27 ` Fangrui Song
2020-08-17 22:44 ` [PATCH 0/4] -ffreestanding/-fno-builtin-* patches H. Peter Anvin
2020-08-18 17:56 ` Nick Desaulniers
2020-08-18 19:02 ` H. Peter Anvin
2020-08-18 19:13 ` Linus Torvalds
2020-08-18 19:25 ` Nick Desaulniers
2020-08-18 19:58 ` Nick Desaulniers
2020-08-19 12:19 ` Clement Courbet
2020-08-18 20:24 ` Arvind Sankar
2020-08-18 20:27 ` Nick Desaulniers
2020-08-18 20:58 ` Nick Desaulniers
2020-08-18 21:41 ` Arvind Sankar
2020-08-18 21:51 ` Dávid Bolvanský
2020-08-18 21:59 ` Nick Desaulniers
2020-08-18 22:05 ` Dávid Bolvanský
2020-08-18 23:22 ` Nick Desaulniers
2020-08-20 14:56 ` Rasmus Villemoes
2020-08-20 17:56 ` Arvind Sankar
2020-08-20 18:05 ` Dávid Bolvanský
2020-08-20 23:33 ` Linus Torvalds
2020-08-21 17:29 ` Arvind Sankar
2020-08-21 17:54 ` Linus Torvalds
2020-08-21 18:02 ` Linus Torvalds
2020-08-21 19:14 ` Arvind Sankar
2020-08-21 19:23 ` Linus Torvalds
2020-08-21 19:57 ` Arvind Sankar
2020-08-21 20:03 ` Peter Zijlstra
2020-08-21 21:39 ` Linus Torvalds
2020-08-22 0:12 ` Nick Desaulniers
2020-08-22 12:20 ` David Laight
2020-08-21 6:45 ` Rasmus Villemoes
2020-08-24 15:57 ` Masahiro Yamada
2020-08-24 17:34 ` Arvind Sankar
2020-08-25 7:10 ` Nick Desaulniers
2020-08-25 7:31 ` Nick Desaulniers
2020-08-25 12:28 ` Masahiro Yamada
2020-08-25 14:02 ` Nick Desaulniers
2020-08-26 13:28 ` Masahiro Yamada
2020-08-18 21:53 ` David Laight
2020-08-20 22:41 ` H. Peter Anvin
2020-08-20 23:17 ` Arvind Sankar
2020-08-18 19:35 ` Nick Desaulniers
2020-08-18 22:25 ` Arvind Sankar
2020-08-18 22:59 ` Nick Desaulniers
2020-08-18 23:51 ` Arvind Sankar
2020-08-19 0:20 ` Arvind Sankar
2020-08-19 8:26 ` David Laight
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