objtool: Support new GCC 6 switch jump table pattern

This fixes some false positive objtool warnings seen with gcc 6.1.1:

  kernel/trace/ring_buffer.o: warning: objtool: ring_buffer_read_page()+0x36c: sibling call from callable instruction with changed frame pointer
  arch/x86/kernel/reboot.o: warning: objtool: native_machine_emergency_restart()+0x139: sibling call from callable instruction with changed frame pointer
  lib/xz/xz_dec_stream.o: warning: objtool: xz_dec_run()+0xc2: sibling call from callable instruction with changed frame pointer

With GCC 6, a new code pattern is sometimes used to access a switch
statement jump table in .rodata, which objtool doesn't yet recognize:

  mov [rodata addr],%reg1
  ... some instructions ...
  jmpq *(%reg1,%reg2,8)

Add support for detecting that pattern.  The detection code is rather
crude, but it's still effective at weeding out false positives and
catching real warnings.  It can be refined later once objtool starts
reading DWARF CFI.

Reported-by: Linus Torvalds <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/b8c9503b4ad8c8a827cc5400db4c1b40a3ea07bc.1469751119.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions