1. 04 May, 2014 8 commits
  2. 03 May, 2014 29 commits
  3. 28 Apr, 2014 2 commits
  4. 27 Apr, 2014 1 commit
    • Will Deacon's avatar
      word-at-a-time: avoid undefined behaviour in zero_bytemask macro · ec6931b2
      Will Deacon authored
      The asm-generic, big-endian version of zero_bytemask creates a mask of
      bytes preceding the first zero-byte by left shifting ~0ul based on the
      position of the first zero byte.
      
      Unfortunately, if the first (top) byte is zero, the output of
      prep_zero_mask has only the top bit set, resulting in undefined C
      behaviour as we shift left by an amount equal to the width of the type.
      As it happens, GCC doesn't manage to spot this through the call to fls(),
      but the issue remains if architectures choose to implement their shift
      instructions differently.
      
      An example would be arch/arm/ (AArch32), where LSL Rd, Rn, #32 results
      in Rd == 0x0, whilst on arch/arm64 (AArch64) LSL Xd, Xn, #64 results in
      Xd == Xn.
      
      Rather than check explicitly for the problematic shift, this patch adds
      an extra shift by 1, replacing fls with __fls. Since zero_bytemask is
      never called with a zero argument (has_zero() is used to check the data
      first), we don't need to worry about calling __fls(0), which is
      undefined.
      
      Cc: <stable@vger.kernel.org>
      Cc: Victor Kamensky <victor.kamensky@linaro.org>
      Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      ec6931b2