objtool: Add Clang support

Since the ORC unwinder was made the default on x86_64, Clang-built
defconfig kernels have triggered some new objtool warnings:

  drivers/gpu/drm/i915/i915_gpu_error.o: warning: objtool: i915_error_printf()+0x6c: return with modified stack frame
  drivers/gpu/drm/i915/intel_display.o: warning: objtool: pipe_config_err()+0xa6: return with modified stack frame

The problem is that objtool has never seen clang-built binaries before.

Shockingly enough, objtool is apparently able to follow the code flow
mostly fine, except for one instruction sequence.  Instead of a LEAVE
instruction, clang restores RSP and RBP the long way:

   67c:   48 89 ec                mov    %rbp,%rsp
   67f:   5d                      pop    %rbp

Teach objtool about this new code sequence.

Reported-and-test-by: Matthias Kaehlcke <mka@chromium.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthias Kaehlcke <mka@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/fce88ce81c356eedcae7f00ed349cfaddb3363cc.1521741586.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 92b6a2c21631..5409f6f6c48d 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1386,6 +1386,17 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state)
                                 state->vals[op->dest.reg].offset = -state->stack_size;
                         }
 
+                        else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
+                                 cfa->base == CFI_BP) {
+
+                                /*
+                                 * mov %rbp, %rsp
+                                 *
+                                 * Restore the original stack pointer (Clang).
+                                 */
+                                state->stack_size = -state->regs[CFI_BP].offset;
+                        }
+
                         else if (op->dest.reg == cfa->base) {
 
                                 /* mov %reg, %rsp */