check.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
 */

#include <string.h>
#include <stdlib.h>

#include "builtin.h"
#include "check.h"
#include "elf.h"
#include "special.h"
#include "arch.h"
#include "warn.h"

#include <linux/hashtable.h>
#include <linux/kernel.h>

#define FAKE_JUMP_OFFSET -1

#define C_JUMP_TABLE_SECTION ".rodata..c_jump_table"

struct alternative {
	struct list_head list;
	struct instruction *insn;
	bool skip_orig;
};

const char *objname;
struct cfi_state initial_func_cfi;

struct instruction *find_insn(struct objtool_file *file,
			      struct section *sec, unsigned long offset)
{
	struct instruction *insn;

	hash_for_each_possible(file->insn_hash, insn, hash, offset)
		if (insn->sec == sec && insn->offset == offset)
			return insn;

	return NULL;
}

static struct instruction *next_insn_same_sec(struct objtool_file *file,
					      struct instruction *insn)
{
	struct instruction *next = list_next_entry(insn, list);

	if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
		return NULL;

	return next;
}

static struct instruction *next_insn_same_func(struct objtool_file *file,
					       struct instruction *insn)
{
	struct instruction *next = list_next_entry(insn, list);
	struct symbol *func = insn->func;

	if (!func)
		return NULL;

	if (&next->list != &file->insn_list && next->func == func)
		return next;

	/* Check if we're already in the subfunction: */
	if (func == func->cfunc)
		return NULL;

	/* Move to the subfunction: */
	return find_insn(file, func->cfunc->sec, func->cfunc->offset);
}

#define func_for_each_insn(file, func, insn)				\
	for (insn = find_insn(file, func->sec, func->offset);		\
	     insn;							\
	     insn = next_insn_same_func(file, insn))

#define sym_for_each_insn(file, sym, insn)				\
	for (insn = find_insn(file, sym->sec, sym->offset);		\
	     insn && &insn->list != &file->insn_list &&			\
		insn->sec == sym->sec &&				\
		insn->offset < sym->offset + sym->len;			\
	     insn = list_next_entry(insn, list))

#define sym_for_each_insn_continue_reverse(file, sym, insn)		\
	for (insn = list_prev_entry(insn, list);			\
	     &insn->list != &file->insn_list &&				\
		insn->sec == sym->sec && insn->offset >= sym->offset;	\
	     insn = list_prev_entry(insn, list))

#define sec_for_each_insn_from(file, insn)				\
	for (; insn; insn = next_insn_same_sec(file, insn))

#define sec_for_each_insn_continue(file, insn)				\
	for (insn = next_insn_same_sec(file, insn); insn;		\
	     insn = next_insn_same_sec(file, insn))

static bool is_static_jump(struct instruction *insn)
{
	return insn->type == INSN_JUMP_CONDITIONAL ||
	       insn->type == INSN_JUMP_UNCONDITIONAL;
}

static bool is_sibling_call(struct instruction *insn)
{
	/* An indirect jump is either a sibling call or a jump to a table. */
	if (insn->type == INSN_JUMP_DYNAMIC)
		return list_empty(&insn->alts);

	if (!is_static_jump(insn))
		return false;

	/* add_jump_destinations() sets insn->call_dest for sibling calls. */
	return !!insn->call_dest;
}

/*
 * This checks to see if the given function is a "noreturn" function.
 *
 * For global functions which are outside the scope of this object file, we
 * have to keep a manual list of them.
 *
 * For local functions, we have to detect them manually by simply looking for
 * the lack of a return instruction.
 */
static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
				int recursion)
{
	int i;
	struct instruction *insn;
	bool empty = true;

	/*
	 * Unfortunately these have to be hard coded because the noreturn
	 * attribute isn't provided in ELF data.
	 */
	static const char * const global_noreturns[] = {
		"__stack_chk_fail",
		"panic",
		"do_exit",
		"do_task_dead",
		"__module_put_and_exit",
		"complete_and_exit",
		"__reiserfs_panic",
		"lbug_with_loc",
		"fortify_panic",
		"usercopy_abort",
		"machine_real_restart",
		"rewind_stack_do_exit",
		"kunit_try_catch_throw",
	};

	if (!func)
		return false;

	if (func->bind == STB_WEAK)
		return false;

	if (func->bind == STB_GLOBAL)
		for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
			if (!strcmp(func->name, global_noreturns[i]))
				return true;

	if (!func->len)
		return false;

	insn = find_insn(file, func->sec, func->offset);
	if (!insn->func)
		return false;

	func_for_each_insn(file, func, insn) {
		empty = false;

		if (insn->type == INSN_RETURN)
			return false;
	}

	if (empty)
		return false;

	/*
	 * A function can have a sibling call instead of a return.  In that
	 * case, the function's dead-end status depends on whether the target
	 * of the sibling call returns.
	 */
	func_for_each_insn(file, func, insn) {
		if (is_sibling_call(insn)) {
			struct instruction *dest = insn->jump_dest;

			if (!dest)
				/* sibling call to another file */
				return false;

			/* local sibling call */
			if (recursion == 5) {
				/*
				 * Infinite recursion: two functions have
				 * sibling calls to each other.  This is a very
				 * rare case.  It means they aren't dead ends.
				 */
				return false;
			}

			return __dead_end_function(file, dest->func, recursion+1);
		}
	}

	return true;
}

static bool dead_end_function(struct objtool_file *file, struct symbol *func)
{
	return __dead_end_function(file, func, 0);
}

static void clear_insn_state(struct insn_state *state)
{
	int i;

	memset(state, 0, sizeof(*state));
	state->cfa.base = CFI_UNDEFINED;
	for (i = 0; i < CFI_NUM_REGS; i++) {
		state->regs[i].base = CFI_UNDEFINED;
		state->vals[i].base = CFI_UNDEFINED;
	}
	state->drap_reg = CFI_UNDEFINED;
	state->drap_offset = -1;
}

/*
 * Call the arch-specific instruction decoder for all the instructions and add
 * them to the global instruction list.
 */
static int decode_instructions(struct objtool_file *file)
{
	struct section *sec;
	struct symbol *func;
	unsigned long offset;
	struct instruction *insn;
	unsigned long nr_insns = 0;
	int ret;

	for_each_sec(file, sec) {

		if (!(sec->sh.sh_flags & SHF_EXECINSTR))
			continue;

		if (strcmp(sec->name, ".altinstr_replacement") &&
		    strcmp(sec->name, ".altinstr_aux") &&
		    strncmp(sec->name, ".discard.", 9))
			sec->text = true;

		for (offset = 0; offset < sec->len; offset += insn->len) {
			insn = malloc(sizeof(*insn));
			if (!insn) {
				WARN("malloc failed");
				return -1;
			}
			memset(insn, 0, sizeof(*insn));
			INIT_LIST_HEAD(&insn->alts);
			clear_insn_state(&insn->state);

			insn->sec = sec;
			insn->offset = offset;

			ret = arch_decode_instruction(file->elf, sec, offset,
						      sec->len - offset,
						      &insn->len, &insn->type,
						      &insn->immediate,
						      &insn->stack_op);
			if (ret)
				goto err;

			hash_add(file->insn_hash, &insn->hash, insn->offset);
			list_add_tail(&insn->list, &file->insn_list);
			nr_insns++;
		}

		list_for_each_entry(func, &sec->symbol_list, list) {
			if (func->type != STT_FUNC || func->alias != func)
				continue;

			if (!find_insn(file, sec, func->offset)) {
				WARN("%s(): can't find starting instruction",
				     func->name);
				return -1;
			}

			sym_for_each_insn(file, func, insn)
				insn->func = func;
		}
	}

	if (stats)
		printf("nr_insns: %lu\n", nr_insns);

	return 0;

err:
	free(insn);
	return ret;
}

/*
 * Mark "ud2" instructions and manually annotated dead ends.
 */
static int add_dead_ends(struct objtool_file *file)
{
	struct section *sec;
	struct rela *rela;
	struct instruction *insn;
	bool found;

	/*
	 * By default, "ud2" is a dead end unless otherwise annotated, because
	 * GCC 7 inserts it for certain divide-by-zero cases.
	 */
	for_each_insn(file, insn)
		if (insn->type == INSN_BUG)
			insn->dead_end = true;

	/*
	 * Check for manually annotated dead ends.
	 */
	sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
	if (!sec)
		goto reachable;

	list_for_each_entry(rela, &sec->rela_list, list) {
		if (rela->sym->type != STT_SECTION) {
			WARN("unexpected relocation symbol type in %s", sec->name);
			return -1;
		}
		insn = find_insn(file, rela->sym->sec, rela->addend);
		if (insn)
			insn = list_prev_entry(insn, list);
		else if (rela->addend == rela->sym->sec->len) {
			found = false;
			list_for_each_entry_reverse(insn, &file->insn_list, list) {
				if (insn->sec == rela->sym->sec) {
					found = true;
					break;
				}
			}

			if (!found) {
				WARN("can't find unreachable insn at %s+0x%x",
				     rela->sym->sec->name, rela->addend);
				return -1;
			}
		} else {
			WARN("can't find unreachable insn at %s+0x%x",
			     rela->sym->sec->name, rela->addend);
			return -1;
		}

		insn->dead_end = true;
	}

reachable:
	/*
	 * These manually annotated reachable checks are needed for GCC 4.4,
	 * where the Linux unreachable() macro isn't supported.  In that case
	 * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
	 * not a dead end.
	 */
	sec = find_section_by_name(file->elf, ".rela.discard.reachable");
	if (!sec)
		return 0;

	list_for_each_entry(rela, &sec->rela_list, list) {
		if (rela->sym->type != STT_SECTION) {
			WARN("unexpected relocation symbol type in %s", sec->name);
			return -1;
		}
		insn = find_insn(file, rela->sym->sec, rela->addend);
		if (insn)
			insn = list_prev_entry(insn, list);
		else if (rela->addend == rela->sym->sec->len) {
			found = false;
			list_for_each_entry_reverse(insn, &file->insn_list, list) {
				if (insn->sec == rela->sym->sec) {
					found = true;
					break;
				}
			}

			if (!found) {
				WARN("can't find reachable insn at %s+0x%x",
				     rela->sym->sec->name, rela->addend);
				return -1;
			}
		} else {
			WARN("can't find reachable insn at %s+0x%x",
			     rela->sym->sec->name, rela->addend);
			return -1;
		}

		insn->dead_end = false;
	}

	return 0;
}

/*
 * Warnings shouldn't be reported for ignored functions.
 */
static void add_ignores(struct objtool_file *file)
{
	struct instruction *insn;
	struct section *sec;
	struct symbol *func;
	struct rela *rela;

	sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
	if (!sec)
		return;

	list_for_each_entry(rela, &sec->rela_list, list) {
		switch (rela->sym->type) {
		case STT_FUNC:
			func = rela->sym;
			break;

		case STT_SECTION:
			func = find_func_by_offset(rela->sym->sec, rela->addend);
			if (!func)
				continue;
			break;

		default:
			WARN("unexpected relocation symbol type in %s: %d", sec->name, rela->sym->type);
			continue;
		}

		func_for_each_insn(file, func, insn)
			insn->ignore = true;
	}
}

/*
 * This is a whitelist of functions that is allowed to be called with AC set.
 * The list is meant to be minimal and only contains compiler instrumentation
 * ABI and a few functions used to implement *_{to,from}_user() functions.
 *
 * These functions must not directly change AC, but may PUSHF/POPF.
 */
static const char *uaccess_safe_builtin[] = {
	/* KASAN */
	"kasan_report",
	"check_memory_region",
	/* KASAN out-of-line */
	"__asan_loadN_noabort",
	"__asan_load1_noabort",
	"__asan_load2_noabort",
	"__asan_load4_noabort",
	"__asan_load8_noabort",
	"__asan_load16_noabort",
	"__asan_storeN_noabort",
	"__asan_store1_noabort",
	"__asan_store2_noabort",
	"__asan_store4_noabort",
	"__asan_store8_noabort",
	"__asan_store16_noabort",
	/* KASAN in-line */
	"__asan_report_load_n_noabort",
	"__asan_report_load1_noabort",
	"__asan_report_load2_noabort",
	"__asan_report_load4_noabort",
	"__asan_report_load8_noabort",
	"__asan_report_load16_noabort",
	"__asan_report_store_n_noabort",
	"__asan_report_store1_noabort",
	"__asan_report_store2_noabort",
	"__asan_report_store4_noabort",
	"__asan_report_store8_noabort",
	"__asan_report_store16_noabort",
	/* KCOV */
	"write_comp_data",
	"__sanitizer_cov_trace_pc",
	"__sanitizer_cov_trace_const_cmp1",
	"__sanitizer_cov_trace_const_cmp2",
	"__sanitizer_cov_trace_const_cmp4",
	"__sanitizer_cov_trace_const_cmp8",
	"__sanitizer_cov_trace_cmp1",
	"__sanitizer_cov_trace_cmp2",
	"__sanitizer_cov_trace_cmp4",
	"__sanitizer_cov_trace_cmp8",
	"__sanitizer_cov_trace_switch",
	/* UBSAN */
	"ubsan_type_mismatch_common",
	"__ubsan_handle_type_mismatch",
	"__ubsan_handle_type_mismatch_v1",
	"__ubsan_handle_shift_out_of_bounds",
	/* misc */
	"csum_partial_copy_generic",
	"__memcpy_mcsafe",
	"mcsafe_handle_tail",
	"ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
	NULL
};

static void add_uaccess_safe(struct objtool_file *file)
{
	struct symbol *func;
	const char **name;

	if (!uaccess)
		return;

	for (name = uaccess_safe_builtin; *name; name++) {
		func = find_symbol_by_name(file->elf, *name);
		if (!func)
			continue;

		func->uaccess_safe = true;
	}
}

/*
 * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 * But it at least allows objtool to understand the control flow *around* the
 * retpoline.
 */
static int add_ignore_alternatives(struct objtool_file *file)
{
	struct section *sec;
	struct rela *rela;
	struct instruction *insn;

	sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
	if (!sec)
		return 0;

	list_for_each_entry(rela, &sec->rela_list, list) {
		if (rela->sym->type != STT_SECTION) {
			WARN("unexpected relocation symbol type in %s", sec->name);
			return -1;
		}

		insn = find_insn(file, rela->sym->sec, rela->addend);
		if (!insn) {
			WARN("bad .discard.ignore_alts entry");
			return -1;
		}

		insn->ignore_alts = true;
	}

	return 0;
}

/*
 * Find the destination instructions for all jumps.
 */
static int add_jump_destinations(struct objtool_file *file)
{
	struct instruction *insn;
	struct rela *rela;
	struct section *dest_sec;
	unsigned long dest_off;

	for_each_insn(file, insn) {
		if (!is_static_jump(insn))
			continue;

		if (insn->ignore || insn->offset == FAKE_JUMP_OFFSET)
			continue;

		rela = find_rela_by_dest_range(file->elf, insn->sec,
					       insn->offset, insn->len);
		if (!rela) {
			dest_sec = insn->sec;
			dest_off = arch_jump_destination(insn);
		} else if (rela->sym->type == STT_SECTION) {
			dest_sec = rela->sym->sec;
			dest_off = arch_dest_rela_offset(rela->addend);
		} else if (rela->sym->sec->idx) {
			dest_sec = rela->sym->sec;
			dest_off = rela->sym->sym.st_value +
				   arch_dest_rela_offset(rela->addend);
		} else if (strstr(rela->sym->name, "_indirect_thunk_")) {
			/*
			 * Retpoline jumps are really dynamic jumps in
			 * disguise, so convert them accordingly.
			 */
			if (insn->type == INSN_JUMP_UNCONDITIONAL)
				insn->type = INSN_JUMP_DYNAMIC;
			else
				insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;

			insn->retpoline_safe = true;
			continue;
		} else {
			/* external sibling call */
			insn->call_dest = rela->sym;
			continue;
		}

		insn->jump_dest = find_insn(file, dest_sec, dest_off);
		if (!insn->jump_dest) {

			/*
			 * This is a special case where an alt instruction
			 * jumps past the end of the section.  These are
			 * handled later in handle_group_alt().
			 */
			if (!strcmp(insn->sec->name, ".altinstr_replacement"))
				continue;

			WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
				  insn->sec, insn->offset, dest_sec->name,
				  dest_off);
			return -1;
		}

		/*
		 * Cross-function jump.
		 */
		if (insn->func && insn->jump_dest->func &&
		    insn->func != insn->jump_dest->func) {

			/*
			 * For GCC 8+, create parent/child links for any cold
			 * subfunctions.  This is _mostly_ redundant with a
			 * similar initialization in read_symbols().
			 *
			 * If a function has aliases, we want the *first* such
			 * function in the symbol table to be the subfunction's
			 * parent.  In that case we overwrite the
			 * initialization done in read_symbols().
			 *
			 * However this code can't completely replace the
			 * read_symbols() code because this doesn't detect the
			 * case where the parent function's only reference to a
			 * subfunction is through a jump table.
			 */
			if (!strstr(insn->func->name, ".cold.") &&
			    strstr(insn->jump_dest->func->name, ".cold.")) {
				insn->func->cfunc = insn->jump_dest->func;
				insn->jump_dest->func->pfunc = insn->func;

			} else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
				   insn->jump_dest->offset == insn->jump_dest->func->offset) {

				/* internal sibling call */
				insn->call_dest = insn->jump_dest->func;
			}
		}
	}

	return 0;
}

/*
 * Find the destination instructions for all calls.
 */
static int add_call_destinations(struct objtool_file *file)
{
	struct instruction *insn;
	unsigned long dest_off;
	struct rela *rela;

	for_each_insn(file, insn) {
		if (insn->type != INSN_CALL)
			continue;

		rela = find_rela_by_dest_range(file->elf, insn->sec,
					       insn->offset, insn->len);
		if (!rela) {
			dest_off = arch_jump_destination(insn);
			insn->call_dest = find_func_by_offset(insn->sec, dest_off);
			if (!insn->call_dest)
				insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);

			if (insn->ignore)
				continue;

			if (!insn->call_dest) {
				WARN_FUNC("unsupported intra-function call",
					  insn->sec, insn->offset);
				if (retpoline)
					WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
				return -1;
			}

			if (insn->func && insn->call_dest->type != STT_FUNC) {
				WARN_FUNC("unsupported call to non-function",
					  insn->sec, insn->offset);
				return -1;
			}

		} else if (rela->sym->type == STT_SECTION) {
			dest_off = arch_dest_rela_offset(rela->addend);
			insn->call_dest = find_func_by_offset(rela->sym->sec,
							      dest_off);
			if (!insn->call_dest) {
				WARN_FUNC("can't find call dest symbol at %s+0x%lx",
					  insn->sec, insn->offset,
					  rela->sym->sec->name,
					  dest_off);
				return -1;
			}
		} else
			insn->call_dest = rela->sym;
	}

	return 0;
}

/*
 * The .alternatives section requires some extra special care, over and above
 * what other special sections require:
 *
 * 1. Because alternatives are patched in-place, we need to insert a fake jump
 *    instruction at the end so that validate_branch() skips all the original
 *    replaced instructions when validating the new instruction path.
 *
 * 2. An added wrinkle is that the new instruction length might be zero.  In
 *    that case the old instructions are replaced with noops.  We simulate that
 *    by creating a fake jump as the only new instruction.
 *
 * 3. In some cases, the alternative section includes an instruction which
 *    conditionally jumps to the _end_ of the entry.  We have to modify these
 *    jumps' destinations to point back to .text rather than the end of the
 *    entry in .altinstr_replacement.
 */
static int handle_group_alt(struct objtool_file *file,
			    struct special_alt *special_alt,
			    struct instruction *orig_insn,
			    struct instruction **new_insn)
{
	struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
	unsigned long dest_off;

	last_orig_insn = NULL;
	insn = orig_insn;
	sec_for_each_insn_from(file, insn) {
		if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
			break;

		insn->alt_group = true;
		last_orig_insn = insn;
	}

	if (next_insn_same_sec(file, last_orig_insn)) {
		fake_jump = malloc(sizeof(*fake_jump));
		if (!fake_jump) {
			WARN("malloc failed");
			return -1;
		}
		memset(fake_jump, 0, sizeof(*fake_jump));
		INIT_LIST_HEAD(&fake_jump->alts);
		clear_insn_state(&fake_jump->state);

		fake_jump->sec = special_alt->new_sec;
		fake_jump->offset = FAKE_JUMP_OFFSET;
		fake_jump->type = INSN_JUMP_UNCONDITIONAL;
		fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
		fake_jump->func = orig_insn->func;
	}

	if (!special_alt->new_len) {
		if (!fake_jump) {
			WARN("%s: empty alternative at end of section",
			     special_alt->orig_sec->name);
			return -1;
		}

		*new_insn = fake_jump;
		return 0;
	}

	last_new_insn = NULL;
	insn = *new_insn;
	sec_for_each_insn_from(file, insn) {
		if (insn->offset >= special_alt->new_off + special_alt->new_len)
			break;

		last_new_insn = insn;

		insn->ignore = orig_insn->ignore_alts;
		insn->func = orig_insn->func;

		/*
		 * Since alternative replacement code is copy/pasted by the
		 * kernel after applying relocations, generally such code can't
		 * have relative-address relocation references to outside the
		 * .altinstr_replacement section, unless the arch's
		 * alternatives code can adjust the relative offsets
		 * accordingly.
		 *
		 * The x86 alternatives code adjusts the offsets only when it
		 * encounters a branch instruction at the very beginning of the
		 * replacement group.
		 */
		if ((insn->offset != special_alt->new_off ||
		    (insn->type != INSN_CALL && !is_static_jump(insn))) &&
		    find_rela_by_dest_range(file->elf, insn->sec, insn->offset, insn->len)) {

			WARN_FUNC("unsupported relocation in alternatives section",
				  insn->sec, insn->offset);
			return -1;
		}

		if (!is_static_jump(insn))
			continue;

		if (!insn->immediate)
			continue;

		dest_off = arch_jump_destination(insn);
		if (dest_off == special_alt->new_off + special_alt->new_len) {
			if (!fake_jump) {
				WARN("%s: alternative jump to end of section",
				     special_alt->orig_sec->name);
				return -1;
			}
			insn->jump_dest = fake_jump;
		}

		if (!insn->jump_dest) {
			WARN_FUNC("can't find alternative jump destination",
				  insn->sec, insn->offset);
			return -1;
		}
	}

	if (!last_new_insn) {
		WARN_FUNC("can't find last new alternative instruction",
			  special_alt->new_sec, special_alt->new_off);
		return -1;
	}

	if (fake_jump)
		list_add(&fake_jump->list, &last_new_insn->list);

	return 0;
}

/*
 * A jump table entry can either convert a nop to a jump or a jump to a nop.
 * If the original instruction is a jump, make the alt entry an effective nop
 * by just skipping the original instruction.
 */
static int handle_jump_alt(struct objtool_file *file,
			   struct special_alt *special_alt,
			   struct instruction *orig_insn,
			   struct instruction **new_insn)
{
	if (orig_insn->type == INSN_NOP)
		return 0;

	if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
		WARN_FUNC("unsupported instruction at jump label",
			  orig_insn->sec, orig_insn->offset);
		return -1;
	}

	*new_insn = list_next_entry(orig_insn, list);
	return 0;
}

/*
 * Read all the special sections which have alternate instructions which can be
 * patched in or redirected to at runtime.  Each instruction having alternate
 * instruction(s) has them added to its insn->alts list, which will be
 * traversed in validate_branch().
 */
static int add_special_section_alts(struct objtool_file *file)
{
	struct list_head special_alts;
	struct instruction *orig_insn, *new_insn;
	struct special_alt *special_alt, *tmp;
	struct alternative *alt;
	int ret;

	ret = special_get_alts(file->elf, &special_alts);
	if (ret)
		return ret;

	list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {

		orig_insn = find_insn(file, special_alt->orig_sec,
				      special_alt->orig_off);
		if (!orig_insn) {
			WARN_FUNC("special: can't find orig instruction",
				  special_alt->orig_sec, special_alt->orig_off);
			ret = -1;
			goto out;
		}

		new_insn = NULL;
		if (!special_alt->group || special_alt->new_len) {
			new_insn = find_insn(file, special_alt->new_sec,
					     special_alt->new_off);
			if (!new_insn) {
				WARN_FUNC("special: can't find new instruction",
					  special_alt->new_sec,
					  special_alt->new_off);
				ret = -1;
				goto out;
			}
		}

		if (special_alt->group) {
			if (!special_alt->orig_len) {
				WARN_FUNC("empty alternative entry",
					  orig_insn->sec, orig_insn->offset);
				continue;
			}

			ret = handle_group_alt(file, special_alt, orig_insn,
					       &new_insn);
			if (ret)
				goto out;
		} else if (special_alt->jump_or_nop) {
			ret = handle_jump_alt(file, special_alt, orig_insn,
					      &new_insn);
			if (ret)
				goto out;
		}

		alt = malloc(sizeof(*alt));
		if (!alt) {
			WARN("malloc failed");
			ret = -1;
			goto out;
		}

		alt->insn = new_insn;
		alt->skip_orig = special_alt->skip_orig;
		orig_insn->ignore_alts |= special_alt->skip_alt;
		list_add_tail(&alt->list, &orig_insn->alts);

		list_del(&special_alt->list);
		free(special_alt);
	}

out:
	return ret;
}

static int add_jump_table(struct objtool_file *file, struct instruction *insn,
			    struct rela *table)
{
	struct rela *rela = table;
	struct instruction *dest_insn;
	struct alternative *alt;
	struct symbol *pfunc = insn->func->pfunc;
	unsigned int prev_offset = 0;

	/*
	 * Each @rela is a switch table relocation which points to the target
	 * instruction.
	 */
	list_for_each_entry_from(rela, &table->sec->rela_list, list) {

		/* Check for the end of the table: */
		if (rela != table && rela->jump_table_start)
			break;

		/* Make sure the table entries are consecutive: */
		if (prev_offset && rela->offset != prev_offset + 8)
			break;

		/* Detect function pointers from contiguous objects: */
		if (rela->sym->sec == pfunc->sec &&
		    rela->addend == pfunc->offset)
			break;

		dest_insn = find_insn(file, rela->sym->sec, rela->addend);
		if (!dest_insn)
			break;

		/* Make sure the destination is in the same function: */
		if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
			break;

		alt = malloc(sizeof(*alt));
		if (!alt) {
			WARN("malloc failed");
			return -1;
		}

		alt->insn = dest_insn;
		list_add_tail(&alt->list, &insn->alts);
		prev_offset = rela->offset;
	}

	if (!prev_offset) {
		WARN_FUNC("can't find switch jump table",
			  insn->sec, insn->offset);
		return -1;
	}

	return 0;
}

/*
 * find_jump_table() - Given a dynamic jump, find the switch jump table in
 * .rodata associated with it.
 *
 * There are 3 basic patterns:
 *
 * 1. jmpq *[rodata addr](,%reg,8)
 *
 *    This is the most common case by far.  It jumps to an address in a simple
 *    jump table which is stored in .rodata.
 *
 * 2. jmpq *[rodata addr](%rip)
 *
 *    This is caused by a rare GCC quirk, currently only seen in three driver
 *    functions in the kernel, only with certain obscure non-distro configs.
 *
 *    As part of an optimization, GCC makes a copy of an existing switch jump
 *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 *    jump) to use a single entry in the table.  The rest of the jump table and
 *    some of its jump targets remain as dead code.
 *
 *    In such a case we can just crudely ignore all unreachable instruction
 *    warnings for the entire object file.  Ideally we would just ignore them
 *    for the function, but that would require redesigning the code quite a
 *    bit.  And honestly that's just not worth doing: unreachable instruction
 *    warnings are of questionable value anyway, and this is such a rare issue.
 *
 * 3. mov [rodata addr],%reg1
 *    ... some instructions ...
 *    jmpq *(%reg1,%reg2,8)
 *
 *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
 *    writing, there are 11 occurrences of it in the allmodconfig kernel.
 *
 *    As of GCC 7 there are quite a few more of these and the 'in between' code
 *    is significant. Esp. with KASAN enabled some of the code between the mov
 *    and jmpq uses .rodata itself, which can confuse things.
 *
 *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 *    ensure the same register is used in the mov and jump instructions.
 *
 *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
 */
static struct rela *find_jump_table(struct objtool_file *file,
				      struct symbol *func,
				      struct instruction *insn)
{
	struct rela *text_rela, *table_rela;
	struct instruction *dest_insn, *orig_insn = insn;
	struct section *table_sec;
	unsigned long table_offset;

	/*
	 * Backward search using the @first_jump_src links, these help avoid
	 * much of the 'in between' code. Which avoids us getting confused by
	 * it.
	 */
	for (;
	     &insn->list != &file->insn_list && insn->func && insn->func->pfunc == func;
	     insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {

		if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
			break;

		/* allow small jumps within the range */
		if (insn->type == INSN_JUMP_UNCONDITIONAL &&
		    insn->jump_dest &&
		    (insn->jump_dest->offset <= insn->offset ||
		     insn->jump_dest->offset > orig_insn->offset))
		    break;

		/* look for a relocation which references .rodata */
		text_rela = find_rela_by_dest_range(file->elf, insn->sec,
						    insn->offset, insn->len);
		if (!text_rela || text_rela->sym->type != STT_SECTION ||
		    !text_rela->sym->sec->rodata)
			continue;

		table_offset = text_rela->addend;
		table_sec = text_rela->sym->sec;

		if (text_rela->type == R_X86_64_PC32)
			table_offset += 4;

		/*
		 * Make sure the .rodata address isn't associated with a
		 * symbol.  GCC jump tables are anonymous data.
		 *
		 * Also support C jump tables which are in the same format as
		 * switch jump tables.  For objtool to recognize them, they
		 * need to be placed in the C_JUMP_TABLE_SECTION section.  They
		 * have symbols associated with them.
		 */
		if (find_symbol_containing(table_sec, table_offset) &&
		    strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
			continue;

		/*
		 * Each table entry has a rela associated with it.  The rela
		 * should reference text in the same function as the original
		 * instruction.
		 */
		table_rela = find_rela_by_dest(file->elf, table_sec, table_offset);
		if (!table_rela)
			continue;
		dest_insn = find_insn(file, table_rela->sym->sec, table_rela->addend);
		if (!dest_insn || !dest_insn->func || dest_insn->func->pfunc != func)
			continue;

		/*
		 * Use of RIP-relative switch jumps is quite rare, and
		 * indicates a rare GCC quirk/bug which can leave dead code
		 * behind.
		 */
		if (text_rela->type == R_X86_64_PC32)
			file->ignore_unreachables = true;

		return table_rela;
	}

	return NULL;
}

/*
 * First pass: Mark the head of each jump table so that in the next pass,
 * we know when a given jump table ends and the next one starts.
 */
static void mark_func_jump_tables(struct objtool_file *file,
				    struct symbol *func)
{
	struct instruction *insn, *last = NULL;
	struct rela *rela;

	func_for_each_insn(file, func, insn) {
		if (!last)
			last = insn;

		/*
		 * Store back-pointers for unconditional forward jumps such
		 * that find_jump_table() can back-track using those and
		 * avoid some potentially confusing code.
		 */
		if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
		    insn->offset > last->offset &&
		    insn->jump_dest->offset > insn->offset &&
		    !insn->jump_dest->first_jump_src) {

			insn->jump_dest->first_jump_src = insn;
			last = insn->jump_dest;
		}

		if (insn->type != INSN_JUMP_DYNAMIC)
			continue;

		rela = find_jump_table(file, func, insn);
		if (rela) {
			rela->jump_table_start = true;
			insn->jump_table = rela;
		}
	}
}

static int add_func_jump_tables(struct objtool_file *file,
				  struct symbol *func)
{
	struct instruction *insn;
	int ret;

	func_for_each_insn(file, func, insn) {
		if (!insn->jump_table)
			continue;

		ret = add_jump_table(file, insn, insn->jump_table);
		if (ret)
			return ret;
	}

	return 0;
}

/*
 * For some switch statements, gcc generates a jump table in the .rodata
 * section which contains a list of addresses within the function to jump to.
 * This finds these jump tables and adds them to the insn->alts lists.
 */
static int add_jump_table_alts(struct objtool_file *file)
{
	struct section *sec;
	struct symbol *func;
	int ret;

	if (!file->rodata)
		return 0;

	for_each_sec(file, sec) {
		list_for_each_entry(func, &sec->symbol_list, list) {
			if (func->type != STT_FUNC)
				continue;

			mark_func_jump_tables(file, func);
			ret = add_func_jump_tables(file, func);
			if (ret)
				return ret;
		}
	}

	return 0;
}

static int read_unwind_hints(struct objtool_file *file)
{
	struct section *sec, *relasec;
	struct rela *rela;
	struct unwind_hint *hint;
	struct instruction *insn;
	struct cfi_reg *cfa;
	int i;

	sec = find_section_by_name(file->elf, ".discard.unwind_hints");
	if (!sec)
		return 0;

	relasec = sec->rela;
	if (!relasec) {
		WARN("missing .rela.discard.unwind_hints section");
		return -1;
	}

	if (sec->len % sizeof(struct unwind_hint)) {
		WARN("struct unwind_hint size mismatch");
		return -1;
	}

	file->hints = true;

	for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
		hint = (struct unwind_hint *)sec->data->d_buf + i;

		rela = find_rela_by_dest(file->elf, sec, i * sizeof(*hint));
		if (!rela) {
			WARN("can't find rela for unwind_hints[%d]", i);
			return -1;
		}

		insn = find_insn(file, rela->sym->sec, rela->addend);
		if (!insn) {
			WARN("can't find insn for unwind_hints[%d]", i);
			return -1;
		}

		cfa = &insn->state.cfa;

		if (hint->type == UNWIND_HINT_TYPE_SAVE) {
			insn->save = true;
			continue;

		} else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
			insn->restore = true;
			insn->hint = true;
			continue;
		}

		insn->hint = true;

		switch (hint->sp_reg) {
		case ORC_REG_UNDEFINED:
			cfa->base = CFI_UNDEFINED;
			break;
		case ORC_REG_SP:
			cfa->base = CFI_SP;
			break;
		case ORC_REG_BP:
			cfa->base = CFI_BP;
			break;
		case ORC_REG_SP_INDIRECT:
			cfa->base = CFI_SP_INDIRECT;
			break;
		case ORC_REG_R10:
			cfa->base = CFI_R10;
			break;
		case ORC_REG_R13:
			cfa->base = CFI_R13;
			break;
		case ORC_REG_DI:
			cfa->base = CFI_DI;
			break;
		case ORC_REG_DX:
			cfa->base = CFI_DX;
			break;
		default:
			WARN_FUNC("unsupported unwind_hint sp base reg %d",
				  insn->sec, insn->offset, hint->sp_reg);
			return -1;
		}

		cfa->offset = hint->sp_offset;
		insn->state.type = hint->type;
		insn->state.end = hint->end;
	}

	return 0;
}

static int read_retpoline_hints(struct objtool_file *file)
{
	struct section *sec;
	struct instruction *insn;
	struct rela *rela;

	sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
	if (!sec)
		return 0;

	list_for_each_entry(rela, &sec->rela_list, list) {
		if (rela->sym->type != STT_SECTION) {
			WARN("unexpected relocation symbol type in %s", sec->name);
			return -1;
		}

		insn = find_insn(file, rela->sym->sec, rela->addend);
		if (!insn) {
			WARN("bad .discard.retpoline_safe entry");
			return -1;
		}

		if (insn->type != INSN_JUMP_DYNAMIC &&
		    insn->type != INSN_CALL_DYNAMIC) {
			WARN_FUNC("retpoline_safe hint not an indirect jump/call",
				  insn->sec, insn->offset);
			return -1;
		}

		insn->retpoline_safe = true;
	}

	return 0;
}

static void mark_rodata(struct objtool_file *file)
{
	struct section *sec;
	bool found = false;

	/*
	 * Search for the following rodata sections, each of which can
	 * potentially contain jump tables:
	 *
	 * - .rodata: can contain GCC switch tables
	 * - .rodata.<func>: same, if -fdata-sections is being used
	 * - .rodata..c_jump_table: contains C annotated jump tables
	 *
	 * .rodata.str1.* sections are ignored; they don't contain jump tables.
	 */
	for_each_sec(file, sec) {
		if ((!strncmp(sec->name, ".rodata", 7) && !strstr(sec->name, ".str1.")) ||
		    !strcmp(sec->name, C_JUMP_TABLE_SECTION)) {
			sec->rodata = true;
			found = true;
		}
	}

	file->rodata = found;
}

static int decode_sections(struct objtool_file *file)
{
	int ret;

	mark_rodata(file);

	ret = decode_instructions(file);
	if (ret)
		return ret;

	ret = add_dead_ends(file);
	if (ret)
		return ret;

	add_ignores(file);
	add_uaccess_safe(file);

	ret = add_ignore_alternatives(file);
	if (ret)
		return ret;

	ret = add_jump_destinations(file);
	if (ret)
		return ret;

	ret = add_special_section_alts(file);
	if (ret)
		return ret;

	ret = add_call_destinations(file);
	if (ret)
		return ret;

	ret = add_jump_table_alts(file);
	if (ret)
		return ret;

	ret = read_unwind_hints(file);
	if (ret)
		return ret;

	ret = read_retpoline_hints(file);
	if (ret)
		return ret;

	return 0;
}

static bool is_fentry_call(struct instruction *insn)
{
	if (insn->type == INSN_CALL &&
	    insn->call_dest->type == STT_NOTYPE &&
	    !strcmp(insn->call_dest->name, "__fentry__"))
		return true;

	return false;
}

static bool has_modified_stack_frame(struct insn_state *state)
{
	int i;

	if (state->cfa.base != initial_func_cfi.cfa.base ||
	    state->cfa.offset != initial_func_cfi.cfa.offset ||
	    state->stack_size != initial_func_cfi.cfa.offset ||
	    state->drap)
		return true;

	for (i = 0; i < CFI_NUM_REGS; i++)
		if (state->regs[i].base != initial_func_cfi.regs[i].base ||
		    state->regs[i].offset != initial_func_cfi.regs[i].offset)
			return true;

	return false;
}

static bool has_valid_stack_frame(struct insn_state *state)
{
	if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
	    state->regs[CFI_BP].offset == -16)
		return true;

	if (state->drap && state->regs[CFI_BP].base == CFI_BP)
		return true;

	return false;
}

static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
{
	struct cfi_reg *cfa = &state->cfa;
	struct stack_op *op = &insn->stack_op;

	if (cfa->base != CFI_SP)
		return 0;

	/* push */
	if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
		cfa->offset += 8;

	/* pop */
	if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
		cfa->offset -= 8;

	/* add immediate to sp */
	if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
	    op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
		cfa->offset -= op->src.offset;

	return 0;
}

static void save_reg(struct insn_state *state, unsigned char reg, int base,
		     int offset)
{
	if (arch_callee_saved_reg(reg) &&
	    state->regs[reg].base == CFI_UNDEFINED) {
		state->regs[reg].base = base;
		state->regs[reg].offset = offset;
	}
}

static void restore_reg(struct insn_state *state, unsigned char reg)
{
	state->regs[reg].base = initial_func_cfi.regs[reg].base;
	state->regs[reg].offset = initial_func_cfi.regs[reg].offset;
}

/*
 * A note about DRAP stack alignment:
 *
 * GCC has the concept of a DRAP register, which is used to help keep track of
 * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
 * register.  The typical DRAP pattern is:
 *
 *   4c 8d 54 24 08		lea    0x8(%rsp),%r10
 *   48 83 e4 c0		and    $0xffffffffffffffc0,%rsp
 *   41 ff 72 f8		pushq  -0x8(%r10)
 *   55				push   %rbp
 *   48 89 e5			mov    %rsp,%rbp
 *				(more pushes)
 *   41 52			push   %r10
 *				...
 *   41 5a			pop    %r10
 *				(more pops)
 *   5d				pop    %rbp
 *   49 8d 62 f8		lea    -0x8(%r10),%rsp
 *   c3				retq
 *
 * There are some variations in the epilogues, like:
 *
 *   5b				pop    %rbx
 *   41 5a			pop    %r10
 *   41 5c			pop    %r12
 *   41 5d			pop    %r13
 *   41 5e			pop    %r14
 *   c9				leaveq
 *   49 8d 62 f8		lea    -0x8(%r10),%rsp
 *   c3				retq
 *
 * and:
 *
 *   4c 8b 55 e8		mov    -0x18(%rbp),%r10
 *   48 8b 5d e0		mov    -0x20(%rbp),%rbx
 *   4c 8b 65 f0		mov    -0x10(%rbp),%r12
 *   4c 8b 6d f8		mov    -0x8(%rbp),%r13
 *   c9				leaveq
 *   49 8d 62 f8		lea    -0x8(%r10),%rsp
 *   c3				retq
 *
 * Sometimes r13 is used as the DRAP register, in which case it's saved and
 * restored beforehand:
 *
 *   41 55			push   %r13
 *   4c 8d 6c 24 10		lea    0x10(%rsp),%r13
 *   48 83 e4 f0		and    $0xfffffffffffffff0,%rsp
 *				...
 *   49 8d 65 f0		lea    -0x10(%r13),%rsp
 *   41 5d			pop    %r13
 *   c3				retq
 */
static int update_insn_state(struct instruction *insn, struct insn_state *state)
{
	struct stack_op *op = &insn->stack_op;
	struct cfi_reg *cfa = &state->cfa;
	struct cfi_reg *regs = state->regs;

	/* stack operations don't make sense with an undefined CFA */
	if (cfa->base == CFI_UNDEFINED) {
		if (insn->func) {
			WARN_FUNC("undefined stack state", insn->sec, insn->offset);
			return -1;
		}
		return 0;
	}

	if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
		return update_insn_state_regs(insn, state);

	switch (op->dest.type) {

	case OP_DEST_REG:
		switch (op->src.type) {

		case OP_SRC_REG:
			if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
			    cfa->base == CFI_SP &&
			    regs[CFI_BP].base == CFI_CFA &&
			    regs[CFI_BP].offset == -cfa->offset) {

				/* mov %rsp, %rbp */
				cfa->base = op->dest.reg;
				state->bp_scratch = false;
			}

			else if (op->src.reg == CFI_SP &&
				 op->dest.reg == CFI_BP && state->drap) {

				/* drap: mov %rsp, %rbp */
				regs[CFI_BP].base = CFI_BP;
				regs[CFI_BP].offset = -state->stack_size;
				state->bp_scratch = false;
			}

			else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {

				/*
				 * mov %rsp, %reg
				 *
				 * This is needed for the rare case where GCC
				 * does:
				 *
				 *   mov    %rsp, %rax
				 *   ...
				 *   mov    %rax, %rsp
				 */
				state->vals[op->dest.reg].base = CFI_CFA;
				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 */
				if (cfa->base == CFI_SP &&
				    state->vals[op->src.reg].base == CFI_CFA) {

					/*
					 * This is needed for the rare case
					 * where GCC does something dumb like:
					 *
					 *   lea    0x8(%rsp), %rcx
					 *   ...
					 *   mov    %rcx, %rsp
					 */
					cfa->offset = -state->vals[op->src.reg].offset;
					state->stack_size = cfa->offset;

				} else {
					cfa->base = CFI_UNDEFINED;
					cfa->offset = 0;
				}
			}

			break;

		case OP_SRC_ADD:
			if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {

				/* add imm, %rsp */
				state->stack_size -= op->src.offset;
				if (cfa->base == CFI_SP)
					cfa->offset -= op->src.offset;
				break;
			}

			if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {

				/* lea disp(%rbp), %rsp */
				state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
				break;
			}

			if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {

				/* drap: lea disp(%rsp), %drap */
				state->drap_reg = op->dest.reg;

				/*
				 * lea disp(%rsp), %reg
				 *
				 * This is needed for the rare case where GCC
				 * does something dumb like:
				 *
				 *   lea    0x8(%rsp), %rcx
				 *   ...
				 *   mov    %rcx, %rsp
				 */
				state->vals[op->dest.reg].base = CFI_CFA;
				state->vals[op->dest.reg].offset = \
					-state->stack_size + op->src.offset;

				break;
			}

			if (state->drap && op->dest.reg == CFI_SP &&
			    op->src.reg == state->drap_reg) {

				 /* drap: lea disp(%drap), %rsp */
				cfa->base = CFI_SP;
				cfa->offset = state->stack_size = -op->src.offset;
				state->drap_reg = CFI_UNDEFINED;
				state->drap = false;
				break;
			}

			if (op->dest.reg == state->cfa.base) {
				WARN_FUNC("unsupported stack register modification",
					  insn->sec, insn->offset);
				return -1;
			}

			break;

		case OP_SRC_AND:
			if (op->dest.reg != CFI_SP ||
			    (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
			    (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
				WARN_FUNC("unsupported stack pointer realignment",
					  insn->sec, insn->offset);
				return -1;
			}

			if (state->drap_reg != CFI_UNDEFINED) {
				/* drap: and imm, %rsp */
				cfa->base = state->drap_reg;
				cfa->offset = state->stack_size = 0;
				state->drap = true;
			}

			/*
			 * Older versions of GCC (4.8ish) realign the stack
			 * without DRAP, with a frame pointer.
			 */

			break;

		case OP_SRC_POP:
		case OP_SRC_POPF:
			if (!state->drap && op->dest.reg == cfa->base) {

				/* pop %rbp */
				cfa->base = CFI_SP;
			}

			if (state->drap && cfa->base == CFI_BP_INDIRECT &&
			    op->dest.reg == state->drap_reg &&
			    state->drap_offset == -state->stack_size) {

				/* drap: pop %drap */
				cfa->base = state->drap_reg;
				cfa->offset = 0;
				state->drap_offset = -1;

			} else if (regs[op->dest.reg].offset == -state->stack_size) {

				/* pop %reg */
				restore_reg(state, op->dest.reg);
			}

			state->stack_size -= 8;
			if (cfa->base == CFI_SP)
				cfa->offset -= 8;

			break;

		case OP_SRC_REG_INDIRECT:
			if (state->drap && op->src.reg == CFI_BP &&
			    op->src.offset == state->drap_offset) {

				/* drap: mov disp(%rbp), %drap */
				cfa->base = state->drap_reg;
				cfa->offset = 0;
				state->drap_offset = -1;
			}

			if (state->drap && op->src.reg == CFI_BP &&
			    op->src.offset == regs[op->dest.reg].offset) {

				/* drap: mov disp(%rbp), %reg */
				restore_reg(state, op->dest.reg);

			} else if (op->src.reg == cfa->base &&
			    op->src.offset == regs[op->dest.reg].offset + cfa->offset) {

				/* mov disp(%rbp), %reg */
				/* mov disp(%rsp), %reg */
				restore_reg(state, op->dest.reg);
			}

			break;

		default:
			WARN_FUNC("unknown stack-related instruction",
				  insn->sec, insn->offset);
			return -1;
		}

		break;

	case OP_DEST_PUSH:
	case OP_DEST_PUSHF:
		state->stack_size += 8;
		if (cfa->base == CFI_SP)
			cfa->offset += 8;

		if (op->src.type != OP_SRC_REG)
			break;

		if (state->drap) {
			if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {

				/* drap: push %drap */
				cfa->base = CFI_BP_INDIRECT;
				cfa->offset = -state->stack_size;

				/* save drap so we know when to restore it */
				state->drap_offset = -state->stack_size;

			} else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {

				/* drap: push %rbp */
				state->stack_size = 0;

			} else if (regs[op->src.reg].base == CFI_UNDEFINED) {

				/* drap: push %reg */
				save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
			}

		} else {

			/* push %reg */
			save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
		}

		/* detect when asm code uses rbp as a scratch register */
		if (!no_fp && insn->func && op->src.reg == CFI_BP &&
		    cfa->base != CFI_BP)
			state->bp_scratch = true;
		break;

	case OP_DEST_REG_INDIRECT:

		if (state->drap) {
			if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {

				/* drap: mov %drap, disp(%rbp) */
				cfa->base = CFI_BP_INDIRECT;
				cfa->offset = op->dest.offset;

				/* save drap offset so we know when to restore it */
				state->drap_offset = op->dest.offset;
			}

			else if (regs[op->src.reg].base == CFI_UNDEFINED) {

				/* drap: mov reg, disp(%rbp) */
				save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
			}

		} else if (op->dest.reg == cfa->base) {

			/* mov reg, disp(%rbp) */
			/* mov reg, disp(%rsp) */
			save_reg(state, op->src.reg, CFI_CFA,
				 op->dest.offset - state->cfa.offset);
		}

		break;

	case OP_DEST_LEAVE:
		if ((!state->drap && cfa->base != CFI_BP) ||
		    (state->drap && cfa->base != state->drap_reg)) {
			WARN_FUNC("leave instruction with modified stack frame",
				  insn->sec, insn->offset);
			return -1;
		}

		/* leave (mov %rbp, %rsp; pop %rbp) */

		state->stack_size = -state->regs[CFI_BP].offset - 8;
		restore_reg(state, CFI_BP);

		if (!state->drap) {
			cfa->base = CFI_SP;
			cfa->offset -= 8;
		}

		break;

	case OP_DEST_MEM:
		if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
			WARN_FUNC("unknown stack-related memory operation",
				  insn->sec, insn->offset);
			return -1;
		}

		/* pop mem */
		state->stack_size -= 8;
		if (cfa->base == CFI_SP)
			cfa->offset -= 8;

		break;

	default:
		WARN_FUNC("unknown stack-related instruction",
			  insn->sec, insn->offset);
		return -1;
	}

	return 0;
}

static bool insn_state_match(struct instruction *insn, struct insn_state *state)
{
	struct insn_state *state1 = &insn->state, *state2 = state;
	int i;

	if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
		WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
			  insn->sec, insn->offset,
			  state1->cfa.base, state1->cfa.offset,
			  state2->cfa.base, state2->cfa.offset);

	} else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
		for (i = 0; i < CFI_NUM_REGS; i++) {
			if (!memcmp(&state1->regs[i], &state2->regs[i],
				    sizeof(struct cfi_reg)))
				continue;

			WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
				  insn->sec, insn->offset,
				  i, state1->regs[i].base, state1->regs[i].offset,
				  i, state2->regs[i].base, state2->regs[i].offset);
			break;
		}

	} else if (state1->type != state2->type) {
		WARN_FUNC("stack state mismatch: type1=%d type2=%d",
			  insn->sec, insn->offset, state1->type, state2->type);

	} else if (state1->drap != state2->drap ||
		 (state1->drap && state1->drap_reg != state2->drap_reg) ||
		 (state1->drap && state1->drap_offset != state2->drap_offset)) {
		WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
			  insn->sec, insn->offset,
			  state1->drap, state1->drap_reg, state1->drap_offset,
			  state2->drap, state2->drap_reg, state2->drap_offset);

	} else
		return true;

	return false;
}

static inline bool func_uaccess_safe(struct symbol *func)
{
	if (func)
		return func->uaccess_safe;

	return false;
}

static inline const char *call_dest_name(struct instruction *insn)
{
	if (insn->call_dest)
		return insn->call_dest->name;

	return "{dynamic}";
}

static int validate_call(struct instruction *insn, struct insn_state *state)
{
	if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
		WARN_FUNC("call to %s() with UACCESS enabled",
				insn->sec, insn->offset, call_dest_name(insn));
		return 1;
	}

	if (state->df) {
		WARN_FUNC("call to %s() with DF set",
				insn->sec, insn->offset, call_dest_name(insn));
		return 1;
	}

	return 0;
}

static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
{
	if (has_modified_stack_frame(state)) {
		WARN_FUNC("sibling call from callable instruction with modified stack frame",
				insn->sec, insn->offset);
		return 1;
	}

	return validate_call(insn, state);
}

static int validate_return(struct symbol *func, struct instruction *insn, struct insn_state *state)
{
	if (state->uaccess && !func_uaccess_safe(func)) {
		WARN_FUNC("return with UACCESS enabled",
			  insn->sec, insn->offset);
		return 1;
	}

	if (!state->uaccess && func_uaccess_safe(func)) {
		WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function",
			  insn->sec, insn->offset);
		return 1;
	}

	if (state->df) {
		WARN_FUNC("return with DF set",
			  insn->sec, insn->offset);
		return 1;
	}

	if (func && has_modified_stack_frame(state)) {
		WARN_FUNC("return with modified stack frame",
			  insn->sec, insn->offset);
		return 1;
	}

	if (state->bp_scratch) {
		WARN_FUNC("BP used as a scratch register",
			  insn->sec, insn->offset);
		return 1;
	}

	return 0;
}

/*
 * Follow the branch starting at the given instruction, and recursively follow
 * any other branches (jumps).  Meanwhile, track the frame pointer state at
 * each instruction and validate all the rules described in
 * tools/objtool/Documentation/stack-validation.txt.
 */
static int validate_branch(struct objtool_file *file, struct symbol *func,
			   struct instruction *first, struct insn_state state)
{
	struct alternative *alt;
	struct instruction *insn, *next_insn;
	struct section *sec;
	u8 visited;
	int ret;

	insn = first;
	sec = insn->sec;

	if (insn->alt_group && list_empty(&insn->alts)) {
		WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
			  sec, insn->offset);
		return 1;
	}

	while (1) {
		next_insn = next_insn_same_sec(file, insn);

		if (file->c_file && func && insn->func && func != insn->func->pfunc) {
			WARN("%s() falls through to next function %s()",
			     func->name, insn->func->name);
			return 1;
		}

		if (func && insn->ignore) {
			WARN_FUNC("BUG: why am I validating an ignored function?",
				  sec, insn->offset);
			return 1;
		}

		visited = 1 << state.uaccess;
		if (insn->visited) {
			if (!insn->hint && !insn_state_match(insn, &state))
				return 1;

			if (insn->visited & visited)
				return 0;
		}

		if (insn->hint) {
			if (insn->restore) {
				struct instruction *save_insn, *i;

				i = insn;
				save_insn = NULL;
				sym_for_each_insn_continue_reverse(file, func, i) {
					if (i->save) {
						save_insn = i;
						break;
					}
				}

				if (!save_insn) {
					WARN_FUNC("no corresponding CFI save for CFI restore",
						  sec, insn->offset);
					return 1;
				}

				if (!save_insn->visited) {
					/*
					 * Oops, no state to copy yet.
					 * Hopefully we can reach this
					 * instruction from another branch
					 * after the save insn has been
					 * visited.
					 */
					if (insn == first)
						return 0;

					WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
						  sec, insn->offset);
					return 1;
				}

				insn->state = save_insn->state;
			}

			state = insn->state;

		} else
			insn->state = state;

		insn->visited |= visited;

		if (!insn->ignore_alts) {
			bool skip_orig = false;

			list_for_each_entry(alt, &insn->alts, list) {
				if (alt->skip_orig)
					skip_orig = true;

				ret = validate_branch(file, func, alt->insn, state);
				if (ret) {
					if (backtrace)
						BT_FUNC("(alt)", insn);
					return ret;
				}
			}

			if (skip_orig)
				return 0;
		}

		switch (insn->type) {

		case INSN_RETURN:
			return validate_return(func, insn, &state);

		case INSN_CALL:
		case INSN_CALL_DYNAMIC:
			ret = validate_call(insn, &state);
			if (ret)
				return ret;

			if (!no_fp && func && !is_fentry_call(insn) &&
			    !has_valid_stack_frame(&state)) {
				WARN_FUNC("call without frame pointer save/setup",
					  sec, insn->offset);
				return 1;
			}

			if (dead_end_function(file, insn->call_dest))
				return 0;

			break;

		case INSN_JUMP_CONDITIONAL:
		case INSN_JUMP_UNCONDITIONAL:
			if (func && is_sibling_call(insn)) {
				ret = validate_sibling_call(insn, &state);
				if (ret)
					return ret;

			} else if (insn->jump_dest) {
				ret = validate_branch(file, func,
						      insn->jump_dest, state);
				if (ret) {
					if (backtrace)
						BT_FUNC("(branch)", insn);
					return ret;
				}
			}

			if (insn->type == INSN_JUMP_UNCONDITIONAL)
				return 0;

			break;

		case INSN_JUMP_DYNAMIC:
		case INSN_JUMP_DYNAMIC_CONDITIONAL:
			if (func && is_sibling_call(insn)) {
				ret = validate_sibling_call(insn, &state);
				if (ret)
					return ret;
			}

			if (insn->type == INSN_JUMP_DYNAMIC)
				return 0;

			break;

		case INSN_CONTEXT_SWITCH:
			if (func && (!next_insn || !next_insn->hint)) {
				WARN_FUNC("unsupported instruction in callable function",
					  sec, insn->offset);
				return 1;
			}
			return 0;

		case INSN_STACK:
			if (update_insn_state(insn, &state))
				return 1;

			if (insn->stack_op.dest.type == OP_DEST_PUSHF) {
				if (!state.uaccess_stack) {
					state.uaccess_stack = 1;
				} else if (state.uaccess_stack >> 31) {
					WARN_FUNC("PUSHF stack exhausted", sec, insn->offset);
					return 1;
				}
				state.uaccess_stack <<= 1;
				state.uaccess_stack  |= state.uaccess;
			}

			if (insn->stack_op.src.type == OP_SRC_POPF) {
				if (state.uaccess_stack) {
					state.uaccess = state.uaccess_stack & 1;
					state.uaccess_stack >>= 1;
					if (state.uaccess_stack == 1)
						state.uaccess_stack = 0;
				}
			}

			break;

		case INSN_STAC:
			if (state.uaccess) {
				WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
				return 1;
			}

			state.uaccess = true;
			break;

		case INSN_CLAC:
			if (!state.uaccess && func) {
				WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
				return 1;
			}

			if (func_uaccess_safe(func) && !state.uaccess_stack) {
				WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
				return 1;
			}

			state.uaccess = false;
			break;

		case INSN_STD:
			if (state.df)
				WARN_FUNC("recursive STD", sec, insn->offset);

			state.df = true;
			break;

		case INSN_CLD:
			if (!state.df && func)
				WARN_FUNC("redundant CLD", sec, insn->offset);

			state.df = false;
			break;

		default:
			break;
		}

		if (insn->dead_end)
			return 0;

		if (!next_insn) {
			if (state.cfa.base == CFI_UNDEFINED)
				return 0;
			WARN("%s: unexpected end of section", sec->name);
			return 1;
		}

		insn = next_insn;
	}

	return 0;
}

static int validate_unwind_hints(struct objtool_file *file)
{
	struct instruction *insn;
	int ret, warnings = 0;
	struct insn_state state;

	if (!file->hints)
		return 0;

	clear_insn_state(&state);

	for_each_insn(file, insn) {
		if (insn->hint && !insn->visited) {
			ret = validate_branch(file, insn->func, insn, state);
			if (ret && backtrace)
				BT_FUNC("<=== (hint)", insn);
			warnings += ret;
		}
	}

	return warnings;
}

static int validate_retpoline(struct objtool_file *file)
{
	struct instruction *insn;
	int warnings = 0;

	for_each_insn(file, insn) {
		if (insn->type != INSN_JUMP_DYNAMIC &&
		    insn->type != INSN_CALL_DYNAMIC)
			continue;

		if (insn->retpoline_safe)
			continue;

		/*
		 * .init.text code is ran before userspace and thus doesn't
		 * strictly need retpolines, except for modules which are
		 * loaded late, they very much do need retpoline in their
		 * .init.text
		 */
		if (!strcmp(insn->sec->name, ".init.text") && !module)
			continue;

		WARN_FUNC("indirect %s found in RETPOLINE build",
			  insn->sec, insn->offset,
			  insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");

		warnings++;
	}

	return warnings;
}

static bool is_kasan_insn(struct instruction *insn)
{
	return (insn->type == INSN_CALL &&
		!strcmp(insn->call_dest->name, "__asan_handle_no_return"));
}

static bool is_ubsan_insn(struct instruction *insn)
{
	return (insn->type == INSN_CALL &&
		!strcmp(insn->call_dest->name,
			"__ubsan_handle_builtin_unreachable"));
}

static bool ignore_unreachable_insn(struct instruction *insn)
{
	int i;

	if (insn->ignore || insn->type == INSN_NOP)
		return true;

	/*
	 * Ignore any unused exceptions.  This can happen when a whitelisted
	 * function has an exception table entry.
	 *
	 * Also ignore alternative replacement instructions.  This can happen
	 * when a whitelisted function uses one of the ALTERNATIVE macros.
	 */
	if (!strcmp(insn->sec->name, ".fixup") ||
	    !strcmp(insn->sec->name, ".altinstr_replacement") ||
	    !strcmp(insn->sec->name, ".altinstr_aux"))
		return true;

	if (!insn->func)
		return false;

	/*
	 * CONFIG_UBSAN_TRAP inserts a UD2 when it sees
	 * __builtin_unreachable().  The BUG() macro has an unreachable() after
	 * the UD2, which causes GCC's undefined trap logic to emit another UD2
	 * (or occasionally a JMP to UD2).
	 */
	if (list_prev_entry(insn, list)->dead_end &&
	    (insn->type == INSN_BUG ||
	     (insn->type == INSN_JUMP_UNCONDITIONAL &&
	      insn->jump_dest && insn->jump_dest->type == INSN_BUG)))
		return true;

	/*
	 * Check if this (or a subsequent) instruction is related to
	 * CONFIG_UBSAN or CONFIG_KASAN.
	 *
	 * End the search at 5 instructions to avoid going into the weeds.
	 */
	for (i = 0; i < 5; i++) {

		if (is_kasan_insn(insn) || is_ubsan_insn(insn))
			return true;

		if (insn->type == INSN_JUMP_UNCONDITIONAL) {
			if (insn->jump_dest &&
			    insn->jump_dest->func == insn->func) {
				insn = insn->jump_dest;
				continue;
			}

			break;
		}

		if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
			break;

		insn = list_next_entry(insn, list);
	}

	return false;
}

static int validate_section(struct objtool_file *file, struct section *sec)
{
	struct symbol *func;
	struct instruction *insn;
	struct insn_state state;
	int ret, warnings = 0;

	list_for_each_entry(func, &sec->symbol_list, list) {
		if (func->type != STT_FUNC)
			continue;

		if (!func->len) {
			WARN("%s() is missing an ELF size annotation",
			     func->name);
			warnings++;
		}

		if (func->pfunc != func || func->alias != func)
			continue;

		insn = find_insn(file, sec, func->offset);
		if (!insn || insn->ignore || insn->visited)
			continue;

		clear_insn_state(&state);
		state.cfa = initial_func_cfi.cfa;
		memcpy(&state.regs, &initial_func_cfi.regs,
		       CFI_NUM_REGS * sizeof(struct cfi_reg));
		state.stack_size = initial_func_cfi.cfa.offset;

		state.uaccess = func->uaccess_safe;

		ret = validate_branch(file, func, insn, state);
		if (ret && backtrace)
			BT_FUNC("<=== (func)", insn);
		warnings += ret;
	}

	return warnings;
}

static int validate_functions(struct objtool_file *file)
{
	struct section *sec;
	int warnings = 0;

	for_each_sec(file, sec)
		warnings += validate_section(file, sec);

	return warnings;
}

static int validate_reachable_instructions(struct objtool_file *file)
{
	struct instruction *insn;

	if (file->ignore_unreachables)
		return 0;

	for_each_insn(file, insn) {
		if (insn->visited || ignore_unreachable_insn(insn))
			continue;

		WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
		return 1;
	}

	return 0;
}

static struct objtool_file file;

int check(const char *_objname, bool orc)
{
	int ret, warnings = 0;

	objname = _objname;

	file.elf = elf_read(objname, orc ? O_RDWR : O_RDONLY);
	if (!file.elf)
		return 1;

	INIT_LIST_HEAD(&file.insn_list);
	hash_init(file.insn_hash);
	file.c_file = find_section_by_name(file.elf, ".comment");
	file.ignore_unreachables = no_unreachable;
	file.hints = false;

	arch_initial_func_cfi_state(&initial_func_cfi);

	ret = decode_sections(&file);
	if (ret < 0)
		goto out;
	warnings += ret;

	if (list_empty(&file.insn_list))
		goto out;

	if (retpoline) {
		ret = validate_retpoline(&file);
		if (ret < 0)
			return ret;
		warnings += ret;
	}

	ret = validate_functions(&file);
	if (ret < 0)
		goto out;
	warnings += ret;

	ret = validate_unwind_hints(&file);
	if (ret < 0)
		goto out;
	warnings += ret;

	if (!warnings) {
		ret = validate_reachable_instructions(&file);
		if (ret < 0)
			goto out;
		warnings += ret;
	}

	if (orc) {
		ret = create_orc(&file);
		if (ret < 0)
			goto out;

		ret = create_orc_sections(&file);
		if (ret < 0)
			goto out;

		ret = elf_write(file.elf);
		if (ret < 0)
			goto out;
	}

out:
	if (ret < 0) {
		/*
		 *  Fatal error.  The binary is corrupt or otherwise broken in
		 *  some way, or objtool itself is broken.  Fail the kernel
		 *  build.
		 */
		return ret;
	}

	return 0;
}