1. 02 10月, 2018 1 次提交
    • A
      x86/vdso: Fix asm constraints on vDSO syscall fallbacks · 715bd9d1
      Andy Lutomirski 提交于
      The syscall fallbacks in the vDSO have incorrect asm constraints.
      They are not marked as writing to their outputs -- instead, they are
      marked as clobbering "memory", which is useless.  In particular, gcc
      is smart enough to know that the timespec parameter hasn't escaped,
      so a memory clobber doesn't clobber it.  And passing a pointer as an
      asm *input* does not tell gcc that the pointed-to value is changed.
      
      Add in the fact that the asm instructions weren't volatile, and gcc
      was free to omit them entirely unless their sole output (the return
      value) is used.  Which it is (phew!), but that stops happening with
      some upcoming patches.
      
      As a trivial example, the following code:
      
      void test_fallback(struct timespec *ts)
      {
      	vdso_fallback_gettime(CLOCK_MONOTONIC, ts);
      }
      
      compiles to:
      
      00000000000000c0 <test_fallback>:
        c0:   c3                      retq
      
      To add insult to injury, the RCX and R11 clobbers on 64-bit
      builds were missing.
      
      The "memory" clobber is also unnecessary -- no ordering with respect to
      other memory operations is needed, but that's going to be fixed in a
      separate not-for-stable patch.
      
      Fixes: 2aae950b ("x86_64: Add vDSO for x86-64 with gettimeofday/clock_gettime/getcpu")
      Signed-off-by: NAndy Lutomirski <luto@kernel.org>
      Signed-off-by: NThomas Gleixner <tglx@linutronix.de>
      Cc: stable@vger.kernel.org
      Link: https://lkml.kernel.org/r/2c0231690551989d2fafa60ed0e7b5cc8b403908.1538422295.git.luto@kernel.org
      715bd9d1
  2. 30 9月, 2018 8 次提交
  3. 29 9月, 2018 12 次提交
  4. 28 9月, 2018 11 次提交
  5. 27 9月, 2018 8 次提交