x86/unwind/orc: Change REG_SP_INDIRECT

Currently REG_SP_INDIRECT is unused but means (%rsp + offset),
change it to mean (%rsp) + offset.

The reason is that we're going to swizzle stack in the middle of a C
function with non-trivial stack footprint. This means that when the
unwinder finds the ToS, it needs to dereference it (%rsp) and then add
the offset to the next frame, resulting in: (%rsp) + offset

This is somewhat unfortunate, since REG_BP_INDIRECT is used (by DRAP)
and thus needs to retain the current (%rbp + offset).
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>

arch/x86/kernel/unwind_orc.c

@@ -471,7 +471,7 @@ bool unwind_next_frame(struct unwind_state *state)
 		break;
 
 	case ORC_REG_SP_INDIRECT:
-		sp = state->sp + orc->sp_offset;
+		sp = state->sp;
 		indirect = true;
 		break;
 
@@ -521,6 +521,9 @@ bool unwind_next_frame(struct unwind_state *state)
 	if (indirect) {
 		if (!deref_stack_reg(state, sp, &sp))
 			goto err;
+
+		if (orc->sp_reg == ORC_REG_SP_INDIRECT)
+			sp += orc->sp_offset;
 	}
 
 	/* Find IP, SP and possibly regs: */

tools/objtool/orc_dump.c

@@ -55,7 +55,7 @@ static void print_reg(unsigned int reg, int offset)
 	if (reg == ORC_REG_BP_INDIRECT)
 		printf("(bp%+d)", offset);
 	else if (reg == ORC_REG_SP_INDIRECT)
-		printf("(sp%+d)", offset);
+		printf("(sp)%+d", offset);
 	else if (reg == ORC_REG_UNDEFINED)
 		printf("(und)");
 	else