releases/4.19.35/lib-string.c-implement-a-basic-bcmp.patch

   1 From d944d9527b3c2dc21ec3418fa17a37b06328a903 Mon Sep 17 00:00:00 2001
   2 From: Nick Desaulniers <ndesaulniers@google.com>
   3 Date: Fri, 5 Apr 2019 18:38:45 -0700
   4 Subject: lib/string.c: implement a basic bcmp
   5
   6 [ Upstream commit 5f074f3e192f10c9fade898b9b3b8812e3d83342 ]
   7
   8 A recent optimization in Clang (r355672) lowers comparisons of the
   9 return value of memcmp against zero to comparisons of the return value
  10 of bcmp against zero.  This helps some platforms that implement bcmp
  11 more efficiently than memcmp.  glibc simply aliases bcmp to memcmp, but
  12 an optimized implementation is in the works.
  13
  14 This results in linkage failures for all targets with Clang due to the
  15 undefined symbol.  For now, just implement bcmp as a tailcail to memcmp
  16 to unbreak the build.  This routine can be further optimized in the
  17 future.
  18
  19 Other ideas discussed:
  20
  21  * A weak alias was discussed, but breaks for architectures that define
  22    their own implementations of memcmp since aliases to declarations are
  23    not permitted (only definitions). Arch-specific memcmp
  24    implementations typically declare memcmp in C headers, but implement
  25    them in assembly.
  26
  27  * -ffreestanding also is used sporadically throughout the kernel.
  28
  29  * -fno-builtin-bcmp doesn't work when doing LTO.
  30
  31 Link: https://bugs.llvm.org/show_bug.cgi?id=41035
  32 Link: https://code.woboq.org/userspace/glibc/string/memcmp.c.html#bcmp
  33 Link: https://github.com/llvm/llvm-project/commit/8e16d73346f8091461319a7dfc4ddd18eedcff13
  34 Link: https://github.com/ClangBuiltLinux/linux/issues/416
  35 Link: http://lkml.kernel.org/r/20190313211335.165605-1-ndesaulniers@google.com
  36 Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
  37 Reported-by: Nathan Chancellor <natechancellor@gmail.com>
  38 Reported-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
  39 Suggested-by: Arnd Bergmann <arnd@arndb.de>
  40 Suggested-by: James Y Knight <jyknight@google.com>
  41 Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
  42 Suggested-by: Nathan Chancellor <natechancellor@gmail.com>
  43 Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
  44 Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
  45 Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
  46 Tested-by: Nathan Chancellor <natechancellor@gmail.com>
  47 Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>
  48 Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
  49 Cc: David Laight <David.Laight@ACULAB.COM>
  50 Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
  51 Cc: Namhyung Kim <namhyung@kernel.org>
  52 Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  53 Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
  54 Cc: Dan Williams <dan.j.williams@intel.com>
  55 Cc: <stable@vger.kernel.org>
  56 Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
  57 Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
  58 Signed-off-by: Sasha Levin <sashal@kernel.org>
  59 ---
  60  include/linux/string.h |  3 +++
  61  lib/string.c           | 20 ++++++++++++++++++++
  62  2 files changed, 23 insertions(+)
  63
  64 diff --git a/include/linux/string.h b/include/linux/string.h
  65 index 4a5a0eb7df51..f58e1ef76572 100644
  66 --- a/include/linux/string.h
  67 +++ b/include/linux/string.h
  68 @@ -143,6 +143,9 @@ extern void * memscan(void *,int,__kernel_size_t);
  69  #ifndef __HAVE_ARCH_MEMCMP
  70  extern int memcmp(const void *,const void *,__kernel_size_t);
  71  #endif
  72 +#ifndef __HAVE_ARCH_BCMP
  73 +extern int bcmp(const void *,const void *,__kernel_size_t);
  74 +#endif
  75  #ifndef __HAVE_ARCH_MEMCHR
  76  extern void * memchr(const void *,int,__kernel_size_t);
  77  #endif
  78 diff --git a/lib/string.c b/lib/string.c
  79 index 2c0900a5d51a..72125fd5b4a6 100644
  80 --- a/lib/string.c
  81 +++ b/lib/string.c
  82 @@ -865,6 +865,26 @@ __visible int memcmp(const void *cs, const void *ct, size_t count)
  83  EXPORT_SYMBOL(memcmp);
  84  #endif
  85
  86 +#ifndef __HAVE_ARCH_BCMP
  87 +/**
  88 + * bcmp - returns 0 if and only if the buffers have identical contents.
  89 + * @a: pointer to first buffer.
  90 + * @b: pointer to second buffer.
  91 + * @len: size of buffers.
  92 + *
  93 + * The sign or magnitude of a non-zero return value has no particular
  94 + * meaning, and architectures may implement their own more efficient bcmp(). So
  95 + * while this particular implementation is a simple (tail) call to memcmp, do
  96 + * not rely on anything but whether the return value is zero or non-zero.
  97 + */
  98 +#undef bcmp
  99 +int bcmp(const void *a, const void *b, size_t len)
 100 +{
 101 +       return memcmp(a, b, len);
 102 +}
 103 +EXPORT_SYMBOL(bcmp);
 104 +#endif
 105 +
 106  #ifndef __HAVE_ARCH_MEMSCAN
 107  /**
 108   * memscan - Find a character in an area of memory.
 109 --
 110 2.19.1
 111