1. 28 Sep, 2017 3 commits
  2. 25 Sep, 2017 13 commits
  3. 23 Sep, 2017 2 commits
    • Josh Poimboeuf's avatar
      x86/asm: Fix inline asm call constraints for Clang · f5caf621
      Josh Poimboeuf authored
      For inline asm statements which have a CALL instruction, we list the
      stack pointer as a constraint to convince GCC to ensure the frame
      pointer is set up first:
      
        static inline void foo()
        {
      	register void *__sp asm(_ASM_SP);
      	asm("call bar" : "+r" (__sp))
        }
      
      Unfortunately, that pattern causes Clang to corrupt the stack pointer.
      
      The fix is easy: convert the stack pointer register variable to a global
      variable.
      
      It should be noted that the end result is different based on the GCC
      version.  With GCC 6.4, this patch has exactly the same result as
      before:
      
      	defconfig	defconfig-nofp	distro		distro-nofp
       before	9820389		9491555		8816046		8516940
       after	9820389		9491555		8816046		8516940
      
      With GCC 7.2, however, GCC's behavior has changed.  It now changes its
      behavior based on the conversion of the register variable to a global.
      That somehow convinces it to *always* set up the frame pointer before
      inserting *any* inline asm.  (Therefore, listing the variable as an
      output constraint is a no-op and is no longer necessary.)  It's a bit
      overkill, but the performance impact should be negligible.  And in fact,
      there's a nice improvement with frame pointers disabled:
      
      	defconfig	defconfig-nofp	distro		distro-nofp
       before	9796316		9468236		9076191		8790305
       after	9796957		9464267		9076381		8785949
      
      So in summary, while listing the stack pointer as an output constraint
      is no longer necessary for newer versions of GCC, it's still needed for
      older versions.
      Suggested-by: 's avatarAndrey Ryabinin <aryabinin@virtuozzo.com>
      Reported-by: 's avatarMatthias Kaehlcke <mka@chromium.org>
      Signed-off-by: 's avatarJosh Poimboeuf <jpoimboe@redhat.com>
      Cc: Alexander Potapenko <glider@google.com>
      Cc: Andy Lutomirski <luto@kernel.org>
      Cc: Arnd Bergmann <arnd@arndb.de>
      Cc: Dmitriy Vyukov <dvyukov@google.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Link: http://lkml.kernel.org/r/3db862e970c432ae823cf515c52b54fec8270e0e.1505942196.git.jpoimboe@redhat.comSigned-off-by: 's avatarIngo Molnar <mingo@kernel.org>
      f5caf621
    • Josh Poimboeuf's avatar
      objtool: Handle another GCC stack pointer adjustment bug · 0d0970ee
      Josh Poimboeuf authored
      The kbuild bot reported the following warning with GCC 4.4 and a
      randconfig:
      
        net/socket.o: warning: objtool: compat_sock_ioctl()+0x1083: stack state mismatch: cfa1=7+160 cfa2=-1+0
      
      This is caused by another GCC non-optimization, where it backs up and
      restores the stack pointer for no apparent reason:
      
          2f91:       48 89 e0                mov    %rsp,%rax
          2f94:       4c 89 e7                mov    %r12,%rdi
          2f97:       4c 89 f6                mov    %r14,%rsi
          2f9a:       ba 20 00 00 00          mov    $0x20,%edx
          2f9f:       48 89 c4                mov    %rax,%rsp
      
      This issue would have been happily ignored before the following commit:
      
        dd88a0a0 ("objtool: Handle GCC stack pointer adjustment bug")
      
      But now that objtool is paying attention to such stack pointer writes
      to/from a register, it needs to understand them properly.  In this case
      that means recognizing that the "mov %rsp, %rax" instruction is
      potentially a backup of the stack pointer.
      Reported-by: 's avatarkbuild test robot <fengguang.wu@intel.com>
      Signed-off-by: 's avatarJosh Poimboeuf <jpoimboe@redhat.com>
      Cc: Alexander Potapenko <glider@google.com>
      Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
      Cc: Andy Lutomirski <luto@kernel.org>
      Cc: Arnd Bergmann <arnd@arndb.de>
      Cc: Dmitriy Vyukov <dvyukov@google.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Cc: Matthias Kaehlcke <mka@chromium.org>
      Cc: Miguel Bernal Marin <miguel.bernal.marin@linux.intel.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Fixes: dd88a0a0 ("objtool: Handle GCC stack pointer adjustment bug")
      Link: http://lkml.kernel.org/r/8c7aa8e9a36fbbb6655d9d8e7cea58958c912da8.1505942196.git.jpoimboe@redhat.comSigned-off-by: 's avatarIngo Molnar <mingo@kernel.org>
      0d0970ee
  4. 21 Sep, 2017 8 commits
  5. 19 Sep, 2017 5 commits
  6. 18 Sep, 2017 7 commits
  7. 15 Sep, 2017 2 commits