objtool: Support '-mtune=atom' stack frame setup instruction

Arnd reported that enabling CONFIG_MATOM results in a bunch of objtool
false positive frame pointer warnings:

  arch/x86/events/intel/ds.o: warning: objtool: intel_pmu_pebs_del()+0x43: call without frame pointer save/setup
  security/keys/keyring.o: warning: objtool: keyring_read()+0x59: call without frame pointer save/setup
  kernel/signal.o: warning: objtool: __dequeue_signal()+0xd8: call without frame pointer save/setup
  ...

objtool gets confused by the fact that the '-mtune=atom' GCC option
sometimes uses 'lea (%rsp),%rbp' instead of 'mov %rsp,%rbp'.  The
instructions are effectively the same, but objtool doesn't know about
the 'lea' variant.

Fix the false warnings by adding support for 'lea (%rsp),%rbp' in the
objtool decoder.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index c0c0b265e88e54b868858a812839c4c24979651e..b63a31be1218830eecc6116cf301f375c0a046c1 100644 (file)
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -98,6 +98,15 @@ int arch_decode_instruction(struct elf *elf, struct section *sec,
                        *type = INSN_FP_SETUP;
                break;
 
+       case 0x8d:
+               if (insn.rex_prefix.bytes &&
+                   insn.rex_prefix.bytes[0] == 0x48 &&
+                   insn.modrm.nbytes && insn.modrm.bytes[0] == 0x2c &&
+                   insn.sib.nbytes && insn.sib.bytes[0] == 0x24)
+                       /* lea %(rsp), %rbp */
+                       *type = INSN_FP_SETUP;
+               break;
+
        case 0x90:
                *type = INSN_NOP;
                break;