x86/unwind/orc: Detect the end of the stack

The existing UNWIND_HINT_EMPTY annotations happen to be good indicators
of where entry code calls into C code for the first time.  So also use
them to mark the end of the stack for the ORC unwinder.

Use that information to set unwind->error if the ORC unwinder doesn't
unwind all the way to the end.  This will be needed for enabling
HAVE_RELIABLE_STACKTRACE for the ORC unwinder so we can use it with the
livepatch consistency model.

Thanks to Jiri Slaby for teaching the ORCs about the unwind hints.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Acked-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>
Link: https://lkml.kernel.org/lkml/20180518064713.26440-5-jslaby@suse.cz
Signed-off-by: Ingo Molnar <mingo@kernel.org>

tools/objtool/arch/x86/include/asm/orc_types.h

@@ -88,6 +88,7 @@ struct orc_entry {
 	unsigned	sp_reg:4;
 	unsigned	bp_reg:4;
 	unsigned	type:2;
+	unsigned	end:1;
 } __packed;
 
 /*
@@ -101,6 +102,7 @@ struct unwind_hint {
 	s16		sp_offset;
 	u8		sp_reg;
 	u8		type;
+	u8		end;
 };
 #endif /* __ASSEMBLY__ */
 

tools/objtool/check.c

@@ -1156,6 +1156,7 @@ static int read_unwind_hints(struct objtool_file *file)
 
 		cfa->offset = hint->sp_offset;
 		insn->state.type = hint->type;
+		insn->state.end = hint->end;
 	}
 
 	return 0;

tools/objtool/check.h

@@ -31,7 +31,7 @@ struct insn_state {
 	int stack_size;
 	unsigned char type;
 	bool bp_scratch;
-	bool drap;
+	bool drap, end;
 	int drap_reg, drap_offset;
 	struct cfi_reg vals[CFI_NUM_REGS];
 };

tools/objtool/orc_dump.c

@@ -203,7 +203,8 @@ int orc_dump(const char *_objname)
 
 		print_reg(orc[i].bp_reg, orc[i].bp_offset);
 
-		printf(" type:%s\n", orc_type_name(orc[i].type));
+		printf(" type:%s end:%d\n",
+		       orc_type_name(orc[i].type), orc[i].end);
 	}
 
 	elf_end(elf);

tools/objtool/orc_gen.c

@@ -31,6 +31,8 @@ int create_orc(struct objtool_file *file)
 		struct cfi_reg *cfa = &insn->state.cfa;
 		struct cfi_reg *bp = &insn->state.regs[CFI_BP];
 
+		orc->end = insn->state.end;
+
 		if (cfa->base == CFI_UNDEFINED) {
 			orc->sp_reg = ORC_REG_UNDEFINED;
 			continue;