[PATCH 2/4] Revert "lib/string.c: implement a basic bcmp"

From: Nick Desaulniers <ndesaulniers@google.com>
To: 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>
Cc: "Michal Marek" <michal.lkml@markovi.net>,
	linux-kbuild@vger.kernel.org, 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>,
	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>,
	"Nick Desaulniers" <ndesaulniers@google.com>
Subject: [PATCH 2/4] Revert "lib/string.c: implement a basic bcmp"
Date: Mon, 17 Aug 2020 15:02:10 -0700	[thread overview]
Message-ID: <20200817220212.338670-3-ndesaulniers@google.com> (raw)
In-Reply-To: <20200817220212.338670-1-ndesaulniers@google.com>

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
 
 # 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

