[PATCH 4.14 083/138] objtool: Add Clang support

[Greg Kroah-Hartman]

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>

commit 3c1f05835cbf9fdfe60b81c718d82ceb94b6c55e upstream.

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@xxxxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/fce88ce81c356eedcae7f00ed349cfaddb3363cc.1521741586.git.jpoimboe@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 tools/objtool/check.c |   11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1385,6 +1385,17 @@ static int update_insn_state(struct inst
 				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 */