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Subject: [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>,
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        Arvind Sankar <nivedita@alum.mit.edu>,
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        Nick Desaulniers <ndesaulniers@google.com>
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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