[PATCH 02/29] objtool: Move checking code to check.c

3 Jun 2018

From: Josh Poimboeuf jpoimboe@redhat.com
commit dcc914f44f065ef73685b37e59877a5bb3cb7358 upstream.
In preparation for the new 'objtool undwarf generate' command, which
will rely on 'objtool check', move the checking code from
builtin-check.c to check.c where it can be used by other commands.
Signed-off-by: Josh Poimboeuf jpoimboe@redhat.com
Reviewed-by: Jiri Slaby jslaby@suse.cz
Cc: Andy Lutomirski luto@kernel.org
Cc: Linus Torvalds torvalds@linux-foundation.org
Cc: Peter Zijlstra peterz@infradead.org
Cc: Thomas Gleixner tglx@linutronix.de
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/294c5c695fd73c1a5000bbe5960a7c9bec4ee6b4.1498659915...
Signed-off-by: Ingo Molnar mingo@kernel.org
[backported by hand to 4.9, this was a pain... - gregkh]
Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
---
 tools/objtool/Build           |    1 +
 tools/objtool/builtin-check.c | 1346 +--------------------------------
 tools/objtool/check.c         | 1327 ++++++++++++++++++++++++++++++++
 tools/objtool/check.h         |   51 ++
 4 files changed, 1392 insertions(+), 1333 deletions(-)
 create mode 100644 tools/objtool/check.c
 create mode 100644 tools/objtool/check.h

diff --git a/tools/objtool/Build b/tools/objtool/Build
index d6cdece5e58b..6f2e1987c4d9 100644
--- a/tools/objtool/Build
+++ b/tools/objtool/Build
@@ -1,5 +1,6 @@
 objtool-y += arch/$(SRCARCH)/
 objtool-y += builtin-check.o
+objtool-y += check.o
 objtool-y += elf.o
 objtool-y += special.o
 objtool-y += objtool.o
diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
index 2aa7313e31f2..365c34ecab26 100644
--- a/tools/objtool/builtin-check.c
+++ b/tools/objtool/builtin-check.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2015 Josh Poimboeuf jpoimboe@redhat.com
+ * Copyright (C) 2015-2017 Josh Poimboeuf jpoimboe@redhat.com
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -25,1352 +25,32 @@
  * For more information, see tools/objtool/Documentation/stack-validation.txt.
  */
-#include <string.h>
-#include <stdlib.h>
 #include <subcmd/parse-options.h>
-
 #include "builtin.h"
-#include "elf.h"
-#include "special.h"
-#include "arch.h"
-#include "warn.h"
-
-#include <linux/hashtable.h>
-
-#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
-
-#define STATE_FP_SAVED		0x1
-#define STATE_FP_SETUP		0x2
-#define STATE_FENTRY		0x4
-
-struct instruction {
-	struct list_head list;
-	struct hlist_node hash;
-	struct section *sec;
-	unsigned long offset;
-	unsigned int len, state;
-	unsigned char type;
-	unsigned long immediate;
-	bool alt_group, visited, dead_end, ignore_alts;
-	struct symbol *call_dest;
-	struct instruction *jump_dest;
-	struct list_head alts;
-	struct symbol *func;
-};
-
-struct alternative {
-	struct list_head list;
-	struct instruction *insn;
-};
-
-struct objtool_file {
-	struct elf *elf;
-	struct list_head insn_list;
-	DECLARE_HASHTABLE(insn_hash, 16);
-	struct section *rodata, *whitelist;
-	bool ignore_unreachables, c_file;
-};
-
-const char *objname;
-static bool nofp;
-
-static 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->list == &file->insn_list || next->sec != insn->sec)
-		return NULL;
-
-	return next;
-}
-
-static bool gcov_enabled(struct objtool_file *file)
-{
-	struct section *sec;
-	struct symbol *sym;
-
-	list_for_each_entry(sec, &file->elf->sections, list)
-		list_for_each_entry(sym, &sec->symbol_list, list)
-			if (!strncmp(sym->name, "__gcov_.", 8))
-				return true;
-
-	return false;
-}
-
-#define for_each_insn(file, insn)					\
-	list_for_each_entry(insn, &file->insn_list, list)
-
-#define func_for_each_insn(file, func, insn)				\
-	for (insn = find_insn(file, func->sec, func->offset);		\
-	     insn && &insn->list != &file->insn_list &&			\
-		insn->sec == func->sec &&				\
-		insn->offset < func->offset + func->len;		\
-	     insn = list_next_entry(insn, list))
-
-#define func_for_each_insn_continue_reverse(file, func, insn)		\
-	for (insn = list_prev_entry(insn, list);			\
-	     &insn->list != &file->insn_list &&				\
-		insn->sec == func->sec && insn->offset >= func->offset;	\
-	     insn = list_prev_entry(insn, list))
-
-#define sec_for_each_insn_from(file, insn)				\
-	for (; insn; insn = next_insn_same_sec(file, insn))
-
-
-/*
- * Check if the function has been manually whitelisted with the
- * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
- * due to its use of a context switching instruction.
- */
-static bool ignore_func(struct objtool_file *file, struct symbol *func)
-{
-	struct rela *rela;
-	struct instruction *insn;
-
-	/* check for STACK_FRAME_NON_STANDARD */
-	if (file->whitelist && file->whitelist->rela)
-		list_for_each_entry(rela, &file->whitelist->rela->rela_list, list) {
-			if (rela->sym->type == STT_SECTION &&
-			    rela->sym->sec == func->sec &&
-			    rela->addend == func->offset)
-				return true;
-			if (rela->sym->type == STT_FUNC && rela->sym == func)
-				return true;
-		}
-
-	/* check if it has a context switching instruction */
-	func_for_each_insn(file, func, insn)
-		if (insn->type == INSN_CONTEXT_SWITCH)
-			return true;
-
-	return false;
-}
-
-/*
- * 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.
- *
- * Returns:
- *  -1: error
- *   0: no dead end
- *   1: dead end
- */
-static int __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",
-		"kvm_spurious_fault",
-		"__reiserfs_panic",
-		"lbug_with_loc"
-	};
-
-	if (func->bind == STB_WEAK)
-		return 0;
-
-	if (func->bind == STB_GLOBAL)
-		for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
-			if (!strcmp(func->name, global_noreturns[i]))
-				return 1;
-
-	if (!func->sec)
-		return 0;
-
-	func_for_each_insn(file, func, insn) {
-		empty = false;
-
-		if (insn->type == INSN_RETURN)
-			return 0;
-	}
-
-	if (empty)
-		return 0;
-
-	/*
-	 * 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 (insn->sec != func->sec ||
-		    insn->offset >= func->offset + func->len)
-			break;
-
-		if (insn->type == INSN_JUMP_UNCONDITIONAL) {
-			struct instruction *dest = insn->jump_dest;
-			struct symbol *dest_func;
-
-			if (!dest)
-				/* sibling call to another file */
-				return 0;
-
-			if (dest->sec != func->sec ||
-			    dest->offset < func->offset ||
-			    dest->offset >= func->offset + func->len) {
-				/* local sibling call */
-				dest_func = find_symbol_by_offset(dest->sec,
-								  dest->offset);
-				if (!dest_func)
-					continue;
-
-				if (recursion == 5) {
-					WARN_FUNC("infinite recursion (objtool bug!)",
-						  dest->sec, dest->offset);
-					return -1;
-				}
-
-				return __dead_end_function(file, dest_func,
-							   recursion + 1);
-			}
-		}
-
-		if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
-			/* sibling call */
-			return 0;
-	}
-
-	return 1;
-}
-
-static int dead_end_function(struct objtool_file *file, struct symbol *func)
-{
-	return __dead_end_function(file, func, 0);
-}
-
-/*
- * 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;
-	int ret;
-
-	list_for_each_entry(sec, &file->elf->sections, list) {
-
-		if (!(sec->sh.sh_flags & SHF_EXECINSTR))
-			continue;
-
-		for (offset = 0; offset < sec->len; offset += insn->len) {
-			insn = malloc(sizeof(*insn));
-			memset(insn, 0, sizeof(*insn));
-
-			INIT_LIST_HEAD(&insn->alts);
-			insn->sec = sec;
-			insn->offset = offset;
-
-			ret = arch_decode_instruction(file->elf, sec, offset,
-						      sec->len - offset,
-						      &insn->len, &insn->type,
-						      &insn->immediate);
-			if (ret)
-				return ret;
-
-			if (!insn->type || insn->type > INSN_LAST) {
-				WARN_FUNC("invalid instruction type %d",
-					  insn->sec, insn->offset, insn->type);
-				return -1;
-			}
-
-			hash_add(file->insn_hash, &insn->hash, insn->offset);
-			list_add_tail(&insn->list, &file->insn_list);
-		}
-
-		list_for_each_entry(func, &sec->symbol_list, list) {
-			if (func->type != STT_FUNC)
-				continue;
-
-			if (!find_insn(file, sec, func->offset)) {
-				WARN("%s(): can't find starting instruction",
-				     func->name);
-				return -1;
-			}
-
-			func_for_each_insn(file, func, insn)
-				if (!insn->func)
-					insn->func = func;
-		}
-	}
-
-	return 0;
-}
-
-/*
- * Find all uses of the unreachable() macro, which are code path dead ends.
- */
-static int add_dead_ends(struct objtool_file *file)
-{
-	struct section *sec;
-	struct rela *rela;
-	struct instruction *insn;
-	bool found;
-
-	sec = find_section_by_name(file->elf, ".rela__unreachable");
-	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 .rela__unreachable");
-			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;
-	}
-
-	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;
-
-	list_for_each_entry(sec, &file->elf->sections, list) {
-		list_for_each_entry(func, &sec->symbol_list, list) {
-			if (func->type != STT_FUNC)
-				continue;
-
-			if (!ignore_func(file, func))
-				continue;
-
-			func_for_each_insn(file, func, insn)
-				insn->visited = 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_nospec_ignores(struct objtool_file *file)
-{
-	struct section *sec;
-	struct rela *rela;
-	struct instruction *insn;
-
-	sec = find_section_by_name(file->elf, ".rela.discard.nospec");
-	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.nospec 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 (insn->type != INSN_JUMP_CONDITIONAL &&
-		    insn->type != INSN_JUMP_UNCONDITIONAL)
-			continue;
-
-		/* skip ignores */
-		if (insn->visited)
-			continue;
-
-		rela = find_rela_by_dest_range(insn->sec, insn->offset,
-					       insn->len);
-		if (!rela) {
-			dest_sec = insn->sec;
-			dest_off = insn->offset + insn->len + insn->immediate;
-		} else if (rela->sym->type == STT_SECTION) {
-			dest_sec = rela->sym->sec;
-			dest_off = rela->addend + 4;
-		} else if (rela->sym->sec->idx) {
-			dest_sec = rela->sym->sec;
-			dest_off = rela->sym->sym.st_value + rela->addend + 4;
-		} else if (strstr(rela->sym->name, "_indirect_thunk_")) {
-			/*
-			 * Retpoline jumps are really dynamic jumps in
-			 * disguise, so convert them accordingly.
-			 */
-			insn->type = INSN_JUMP_DYNAMIC;
-			continue;
-		} else {
-			/* sibling call */
-			insn->jump_dest = 0;
-			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;
-		}
-	}
-
-	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(insn->sec, insn->offset,
-					       insn->len);
-		if (!rela) {
-			dest_off = insn->offset + insn->len + insn->immediate;
-			insn->call_dest = find_symbol_by_offset(insn->sec,
-								dest_off);
-			/*
-			 * FIXME: Thanks to retpolines, it's now considered
-			 * normal for a function to call within itself.  So
-			 * disable this warning for now.
-			 */
-#if 0
-			if (!insn->call_dest) {
-				WARN_FUNC("can't find call dest symbol at offset 0x%lx",
-					  insn->sec, insn->offset, dest_off);
-				return -1;
-			}
-#endif
-		} else if (rela->sym->type == STT_SECTION) {
-			insn->call_dest = find_symbol_by_offset(rela->sym->sec,
-								rela->addend+4);
-			if (!insn->call_dest ||
-			    insn->call_dest->type != STT_FUNC) {
-				WARN_FUNC("can't find call dest symbol at %s+0x%x",
-					  insn->sec, insn->offset,
-					  rela->sym->sec->name,
-					  rela->addend + 4);
-				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.
- *
- * 4. It has been requested that we don't validate the !POPCNT feature path
- *    which is a "very very small percentage of machines".
- */
-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;
-	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;
-
-		if (special_alt->skip_orig)
-			insn->type = INSN_NOP;
-
-		insn->alt_group = true;
-		last_orig_insn = insn;
-	}
-
-	if (!next_insn_same_sec(file, last_orig_insn)) {
-		WARN("%s: don't know how to handle alternatives at end of section",
-		     special_alt->orig_sec->name);
-		return -1;
-	}
-
-	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);
-	fake_jump->sec = special_alt->new_sec;
-	fake_jump->offset = -1;
-	fake_jump->type = INSN_JUMP_UNCONDITIONAL;
-	fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
-
-	if (!special_alt->new_len) {
-		*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;
-
-		if (insn->type != INSN_JUMP_CONDITIONAL &&
-		    insn->type != INSN_JUMP_UNCONDITIONAL)
-			continue;
-
-		if (!insn->immediate)
-			continue;
-
-		dest_off = insn->offset + insn->len + insn->immediate;
-		if (dest_off == special_alt->new_off + special_alt->new_len)
-			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;
-	}
-
-	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;
+#include "check.h"
-	ret = special_get_alts(file->elf, &special_alts);
-	if (ret)
-		return ret;
+bool nofp;
-	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;
-		}
-
-		/* Ignore retpoline alternatives. */
-		if (orig_insn->ignore_alts)
-			continue;
-
-		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) {
-			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;
-		list_add_tail(&alt->list, &orig_insn->alts);
-
-		list_del(&special_alt->list);
-		free(special_alt);
-	}
-
-out:
-	return ret;
-}
-
-static int add_switch_table(struct objtool_file *file, struct symbol *func,
-			    struct instruction *insn, struct rela *table,
-			    struct rela *next_table)
-{
-	struct rela *rela = table;
-	struct instruction *alt_insn;
-	struct alternative *alt;
-
-	list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
-		if (rela == next_table)
-			break;
-
-		if (rela->sym->sec != insn->sec ||
-		    rela->addend <= func->offset ||
-		    rela->addend >= func->offset + func->len)
-			break;
-
-		alt_insn = find_insn(file, insn->sec, rela->addend);
-		if (!alt_insn) {
-			WARN("%s: can't find instruction at %s+0x%x",
-			     file->rodata->rela->name, insn->sec->name,
-			     rela->addend);
-			return -1;
-		}
-
-		alt = malloc(sizeof(*alt));
-		if (!alt) {
-			WARN("malloc failed");
-			return -1;
-		}
-
-		alt->insn = alt_insn;
-		list_add_tail(&alt->list, &insn->alts);
-	}
-
-	return 0;
-}
-
-/*
- * find_switch_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.
- *
- *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
- *    ensure the same register is used in the mov and jump instructions.
- */
-static struct rela *find_switch_table(struct objtool_file *file,
-				      struct symbol *func,
-				      struct instruction *insn)
-{
-	struct rela *text_rela, *rodata_rela;
-	struct instruction *orig_insn = insn;
-
-	text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
-	if (text_rela && text_rela->sym == file->rodata->sym) {
-		/* case 1 */
-		rodata_rela = find_rela_by_dest(file->rodata,
-						text_rela->addend);
-		if (rodata_rela)
-			return rodata_rela;
-
-		/* case 2 */
-		rodata_rela = find_rela_by_dest(file->rodata,
-						text_rela->addend + 4);
-		if (!rodata_rela)
-			return NULL;
-		file->ignore_unreachables = true;
-		return rodata_rela;
-	}
-
-	/* case 3 */
-	func_for_each_insn_continue_reverse(file, func, insn) {
-		if (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(insn->sec, insn->offset,
-						    insn->len);
-		if (!text_rela || text_rela->sym != file->rodata->sym)
-			continue;
-
-		/*
-		 * Make sure the .rodata address isn't associated with a
-		 * symbol.  gcc jump tables are anonymous data.
-		 */
-		if (find_symbol_containing(file->rodata, text_rela->addend))
-			continue;
-
-		return find_rela_by_dest(file->rodata, text_rela->addend);
-	}
-
-	return NULL;
-}
-
-static int add_func_switch_tables(struct objtool_file *file,
-				  struct symbol *func)
-{
-	struct instruction *insn, *prev_jump = NULL;
-	struct rela *rela, *prev_rela = NULL;
-	int ret;
-
-	func_for_each_insn(file, func, insn) {
-		if (insn->type != INSN_JUMP_DYNAMIC)
-			continue;
-
-		rela = find_switch_table(file, func, insn);
-		if (!rela)
-			continue;
-
-		/*
-		 * We found a switch table, but we don't know yet how big it
-		 * is.  Don't add it until we reach the end of the function or
-		 * the beginning of another switch table in the same function.
-		 */
-		if (prev_jump) {
-			ret = add_switch_table(file, func, prev_jump, prev_rela,
-					       rela);
-			if (ret)
-				return ret;
-		}
-
-		prev_jump = insn;
-		prev_rela = rela;
-	}
-
-	if (prev_jump) {
-		ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
-		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_switch_table_alts(struct objtool_file *file)
-{
-	struct section *sec;
-	struct symbol *func;
-	int ret;
-
-	if (!file->rodata || !file->rodata->rela)
-		return 0;
-
-	list_for_each_entry(sec, &file->elf->sections, list) {
-		list_for_each_entry(func, &sec->symbol_list, list) {
-			if (func->type != STT_FUNC)
-				continue;
-
-			ret = add_func_switch_tables(file, func);
-			if (ret)
-				return ret;
-		}
-	}
-
-	return 0;
-}
-
-static int decode_sections(struct objtool_file *file)
-{
-	int ret;
-
-	ret = decode_instructions(file);
-	if (ret)
-		return ret;
-
-	ret = add_dead_ends(file);
-	if (ret)
-		return ret;
-
-	add_ignores(file);
-
-	ret = add_nospec_ignores(file);
-	if (ret)
-		return ret;
-
-	ret = add_jump_destinations(file);
-	if (ret)
-		return ret;
-
-	ret = add_call_destinations(file);
-	if (ret)
-		return ret;
-
-	ret = add_special_section_alts(file);
-	if (ret)
-		return ret;
-
-	ret = add_switch_table_alts(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 instruction *insn)
-{
-	return (insn->state & STATE_FP_SAVED) ||
-	       (insn->state & STATE_FP_SETUP);
-}
-
-static bool has_valid_stack_frame(struct instruction *insn)
-{
-	return (insn->state & STATE_FP_SAVED) &&
-	       (insn->state & STATE_FP_SETUP);
-}
-
-static unsigned int frame_state(unsigned long state)
-{
-	return (state & (STATE_FP_SAVED | STATE_FP_SETUP));
-}
-
-/*
- * 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 instruction *first, unsigned char first_state)
-{
-	struct alternative *alt;
-	struct instruction *insn;
-	struct section *sec;
-	struct symbol *func = NULL;
-	unsigned char state;
-	int ret;
-
-	insn = first;
-	sec = insn->sec;
-	state = first_state;
-
-	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) {
-		if (file->c_file && insn->func) {
-			if (func && func != insn->func) {
-				WARN("%s() falls through to next function %s()",
-				     func->name, insn->func->name);
-				return 1;
-			}
-
-			func = insn->func;
-		}
-
-		if (insn->visited) {
-			if (frame_state(insn->state) != frame_state(state)) {
-				WARN_FUNC("frame pointer state mismatch",
-					  sec, insn->offset);
-				return 1;
-			}
-
-			return 0;
-		}
-
-		insn->visited = true;
-		insn->state = state;
-
-		list_for_each_entry(alt, &insn->alts, list) {
-			ret = validate_branch(file, alt->insn, state);
-			if (ret)
-				return 1;
-		}
-
-		switch (insn->type) {
-
-		case INSN_FP_SAVE:
-			if (!nofp) {
-				if (state & STATE_FP_SAVED) {
-					WARN_FUNC("duplicate frame pointer save",
-						  sec, insn->offset);
-					return 1;
-				}
-				state |= STATE_FP_SAVED;
-			}
-			break;
-
-		case INSN_FP_SETUP:
-			if (!nofp) {
-				if (state & STATE_FP_SETUP) {
-					WARN_FUNC("duplicate frame pointer setup",
-						  sec, insn->offset);
-					return 1;
-				}
-				state |= STATE_FP_SETUP;
-			}
-			break;
-
-		case INSN_FP_RESTORE:
-			if (!nofp) {
-				if (has_valid_stack_frame(insn))
-					state &= ~STATE_FP_SETUP;
-
-				state &= ~STATE_FP_SAVED;
-			}
-			break;
-
-		case INSN_RETURN:
-			if (!nofp && has_modified_stack_frame(insn)) {
-				WARN_FUNC("return without frame pointer restore",
-					  sec, insn->offset);
-				return 1;
-			}
-			return 0;
-
-		case INSN_CALL:
-			if (is_fentry_call(insn)) {
-				state |= STATE_FENTRY;
-				break;
-			}
-
-			ret = dead_end_function(file, insn->call_dest);
-			if (ret == 1)
-				return 0;
-			if (ret == -1)
-				return 1;
-
-			/* fallthrough */
-		case INSN_CALL_DYNAMIC:
-			if (!nofp && !has_valid_stack_frame(insn)) {
-				WARN_FUNC("call without frame pointer save/setup",
-					  sec, insn->offset);
-				return 1;
-			}
-			break;
-
-		case INSN_JUMP_CONDITIONAL:
-		case INSN_JUMP_UNCONDITIONAL:
-			if (insn->jump_dest) {
-				ret = validate_branch(file, insn->jump_dest,
-						      state);
-				if (ret)
-					return 1;
-			} else if (has_modified_stack_frame(insn)) {
-				WARN_FUNC("sibling call from callable instruction with changed frame pointer",
-					  sec, insn->offset);
-				return 1;
-			} /* else it's a sibling call */
-
-			if (insn->type == INSN_JUMP_UNCONDITIONAL)
-				return 0;
-
-			break;
-
-		case INSN_JUMP_DYNAMIC:
-			if (list_empty(&insn->alts) &&
-			    has_modified_stack_frame(insn)) {
-				WARN_FUNC("sibling call from callable instruction with changed frame pointer",
-					  sec, insn->offset);
-				return 1;
-			}
-
-			return 0;
-
-		default:
-			break;
-		}
-
-		if (insn->dead_end)
-			return 0;
-
-		insn = next_insn_same_sec(file, insn);
-		if (!insn) {
-			WARN("%s: unexpected end of section", sec->name);
-			return 1;
-		}
-	}
-
-	return 0;
-}
-
-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 symbol *func,
-				    struct instruction *insn)
-{
-	int i;
-
-	if (insn->type == INSN_NOP)
-		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 && insn->jump_dest) {
-			insn = insn->jump_dest;
-			continue;
-		}
-
-		if (insn->offset + insn->len >= func->offset + func->len)
-			break;
-		insn = list_next_entry(insn, list);
-	}
-
-	return false;
-}
-
-static int validate_functions(struct objtool_file *file)
-{
-	struct section *sec;
-	struct symbol *func;
-	struct instruction *insn;
-	int ret, warnings = 0;
-
-	list_for_each_entry(sec, &file->elf->sections, list) {
-		list_for_each_entry(func, &sec->symbol_list, list) {
-			if (func->type != STT_FUNC)
-				continue;
-
-			insn = find_insn(file, sec, func->offset);
-			if (!insn)
-				continue;
-
-			ret = validate_branch(file, insn, 0);
-			warnings += ret;
-		}
-	}
-
-	list_for_each_entry(sec, &file->elf->sections, list) {
-		list_for_each_entry(func, &sec->symbol_list, list) {
-			if (func->type != STT_FUNC)
-				continue;
-
-			func_for_each_insn(file, func, insn) {
-				if (insn->visited)
-					continue;
-
-				insn->visited = true;
-
-				if (file->ignore_unreachables || warnings ||
-				    ignore_unreachable_insn(func, insn))
-					continue;
-
-				/*
-				 * gcov produces a lot of unreachable
-				 * instructions.  If we get an unreachable
-				 * warning and the file has gcov enabled, just
-				 * ignore it, and all other such warnings for
-				 * the file.
-				 */
-				if (!file->ignore_unreachables &&
-				    gcov_enabled(file)) {
-					file->ignore_unreachables = true;
-					continue;
-				}
-
-				WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
-				warnings++;
-			}
-		}
-	}
-
-	return warnings;
-}
-
-static int validate_uncallable_instructions(struct objtool_file *file)
-{
-	struct instruction *insn;
-	int warnings = 0;
-
-	for_each_insn(file, insn) {
-		if (!insn->visited && insn->type == INSN_RETURN) {
-
-			/*
-			 * Don't warn about call instructions in unvisited
-			 * retpoline alternatives.
-			 */
-			if (!strcmp(insn->sec->name, ".altinstr_replacement"))
-				continue;
-
-			WARN_FUNC("return instruction outside of a callable function",
-				  insn->sec, insn->offset);
-			warnings++;
-		}
-	}
-
-	return warnings;
-}
-
-static void cleanup(struct objtool_file *file)
-{
-	struct instruction *insn, *tmpinsn;
-	struct alternative *alt, *tmpalt;
-
-	list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
-		list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
-			list_del(&alt->list);
-			free(alt);
-		}
-		list_del(&insn->list);
-		hash_del(&insn->hash);
-		free(insn);
-	}
-	elf_close(file->elf);
-}
-
-const char * const check_usage[] = {
+static const char * const check_usage[] = {
    "objtool check [<options>] file.o",
    NULL,
 };
+const struct option check_options[] = {
+	OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),
+	OPT_END(),
+};
+
 int cmd_check(int argc, const char **argv)
 {
-	struct objtool_file file;
-	int ret, warnings = 0;
+	const char *objname;
-	const struct option options[] = {
-		OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),
-		OPT_END(),
-	};
-
-	argc = parse_options(argc, argv, options, check_usage, 0);
+	argc = parse_options(argc, argv, check_options, check_usage, 0);
if (argc != 1)
-		usage_with_options(check_usage, options);
+		usage_with_options(check_usage, check_options);
objname = argv[0];
-	file.elf = elf_open(objname);
-	if (!file.elf) {
-		fprintf(stderr, "error reading elf file %s\n", objname);
-		return 1;
-	}
-
-	INIT_LIST_HEAD(&file.insn_list);
-	hash_init(file.insn_hash);
-	file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
-	file.rodata = find_section_by_name(file.elf, ".rodata");
-	file.ignore_unreachables = false;
-	file.c_file = find_section_by_name(file.elf, ".comment");
-
-	ret = decode_sections(&file);
-	if (ret < 0)
-		goto out;
-	warnings += ret;
-
-	ret = validate_functions(&file);
-	if (ret < 0)
-		goto out;
-	warnings += ret;
-
-	ret = validate_uncallable_instructions(&file);
-	if (ret < 0)
-		goto out;
-	warnings += ret;
-
-out:
-	cleanup(&file);
-
-	/* ignore warnings for now until we get all the code cleaned up */
-	if (ret || warnings)
-		return 0;
-	return 0;
+	return check(objname, nofp);
 }
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
new file mode 100644
index 000000000000..b7a0af57a43d
--- /dev/null
+++ b/tools/objtool/check.c
@@ -0,0 +1,1327 @@
+/*
+ * Copyright (C) 2015-2017 Josh Poimboeuf jpoimboe@redhat.com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see http://www.gnu.org/licenses/.
+ */
+
+#include <string.h>
+#include <stdlib.h>
+
+#include "check.h"
+#include "elf.h"
+#include "special.h"
+#include "arch.h"
+#include "warn.h"
+
+#include <linux/hashtable.h>
+
+#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
+
+#define STATE_FP_SAVED		0x1
+#define STATE_FP_SETUP		0x2
+#define STATE_FENTRY		0x4
+
+struct alternative {
+	struct list_head list;
+	struct instruction *insn;
+};
+
+const char *objname;
+static bool nofp;
+
+static 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->list == &file->insn_list || next->sec != insn->sec)
+		return NULL;
+
+	return next;
+}
+
+static bool gcov_enabled(struct objtool_file *file)
+{
+	struct section *sec;
+	struct symbol *sym;
+
+	list_for_each_entry(sec, &file->elf->sections, list)
+		list_for_each_entry(sym, &sec->symbol_list, list)
+			if (!strncmp(sym->name, "__gcov_.", 8))
+				return true;
+
+	return false;
+}
+
+#define for_each_insn(file, insn)					\
+	list_for_each_entry(insn, &file->insn_list, list)
+
+#define func_for_each_insn(file, func, insn)				\
+	for (insn = find_insn(file, func->sec, func->offset);		\
+	     insn && &insn->list != &file->insn_list &&			\
+		insn->sec == func->sec &&				\
+		insn->offset < func->offset + func->len;		\
+	     insn = list_next_entry(insn, list))
+
+#define func_for_each_insn_continue_reverse(file, func, insn)		\
+	for (insn = list_prev_entry(insn, list);			\
+	     &insn->list != &file->insn_list &&				\
+		insn->sec == func->sec && insn->offset >= func->offset;	\
+	     insn = list_prev_entry(insn, list))
+
+#define sec_for_each_insn_from(file, insn)				\
+	for (; insn; insn = next_insn_same_sec(file, insn))
+
+
+/*
+ * Check if the function has been manually whitelisted with the
+ * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
+ * due to its use of a context switching instruction.
+ */
+static bool ignore_func(struct objtool_file *file, struct symbol *func)
+{
+	struct rela *rela;
+	struct instruction *insn;
+
+	/* check for STACK_FRAME_NON_STANDARD */
+	if (file->whitelist && file->whitelist->rela)
+		list_for_each_entry(rela, &file->whitelist->rela->rela_list, list) {
+			if (rela->sym->type == STT_SECTION &&
+			    rela->sym->sec == func->sec &&
+			    rela->addend == func->offset)
+				return true;
+			if (rela->sym->type == STT_FUNC && rela->sym == func)
+				return true;
+		}
+
+	/* check if it has a context switching instruction */
+	func_for_each_insn(file, func, insn)
+		if (insn->type == INSN_CONTEXT_SWITCH)
+			return true;
+
+	return false;
+}
+
+/*
+ * 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.
+ *
+ * Returns:
+ *  -1: error
+ *   0: no dead end
+ *   1: dead end
+ */
+static int __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",
+		"kvm_spurious_fault",
+		"__reiserfs_panic",
+		"lbug_with_loc"
+	};
+
+	if (func->bind == STB_WEAK)
+		return 0;
+
+	if (func->bind == STB_GLOBAL)
+		for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
+			if (!strcmp(func->name, global_noreturns[i]))
+				return 1;
+
+	if (!func->sec)
+		return 0;
+
+	func_for_each_insn(file, func, insn) {
+		empty = false;
+
+		if (insn->type == INSN_RETURN)
+			return 0;
+	}
+
+	if (empty)
+		return 0;
+
+	/*
+	 * 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 (insn->sec != func->sec ||
+		    insn->offset >= func->offset + func->len)
+			break;
+
+		if (insn->type == INSN_JUMP_UNCONDITIONAL) {
+			struct instruction *dest = insn->jump_dest;
+			struct symbol *dest_func;
+
+			if (!dest)
+				/* sibling call to another file */
+				return 0;
+
+			if (dest->sec != func->sec ||
+			    dest->offset < func->offset ||
+			    dest->offset >= func->offset + func->len) {
+				/* local sibling call */
+				dest_func = find_symbol_by_offset(dest->sec,
+								  dest->offset);
+				if (!dest_func)
+					continue;
+
+				if (recursion == 5) {
+					WARN_FUNC("infinite recursion (objtool bug!)",
+						  dest->sec, dest->offset);
+					return -1;
+				}
+
+				return __dead_end_function(file, dest_func,
+							   recursion + 1);
+			}
+		}
+
+		if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
+			/* sibling call */
+			return 0;
+	}
+
+	return 1;
+}
+
+static int dead_end_function(struct objtool_file *file, struct symbol *func)
+{
+	return __dead_end_function(file, func, 0);
+}
+
+/*
+ * 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;
+	int ret;
+
+	list_for_each_entry(sec, &file->elf->sections, list) {
+
+		if (!(sec->sh.sh_flags & SHF_EXECINSTR))
+			continue;
+
+		for (offset = 0; offset < sec->len; offset += insn->len) {
+			insn = malloc(sizeof(*insn));
+			memset(insn, 0, sizeof(*insn));
+
+			INIT_LIST_HEAD(&insn->alts);
+			insn->sec = sec;
+			insn->offset = offset;
+
+			ret = arch_decode_instruction(file->elf, sec, offset,
+						      sec->len - offset,
+						      &insn->len, &insn->type,
+						      &insn->immediate);
+			if (ret)
+				return ret;
+
+			if (!insn->type || insn->type > INSN_LAST) {
+				WARN_FUNC("invalid instruction type %d",
+					  insn->sec, insn->offset, insn->type);
+				return -1;
+			}
+
+			hash_add(file->insn_hash, &insn->hash, insn->offset);
+			list_add_tail(&insn->list, &file->insn_list);
+		}
+
+		list_for_each_entry(func, &sec->symbol_list, list) {
+			if (func->type != STT_FUNC)
+				continue;
+
+			if (!find_insn(file, sec, func->offset)) {
+				WARN("%s(): can't find starting instruction",
+				     func->name);
+				return -1;
+			}
+
+			func_for_each_insn(file, func, insn)
+				if (!insn->func)
+					insn->func = func;
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * Find all uses of the unreachable() macro, which are code path dead ends.
+ */
+static int add_dead_ends(struct objtool_file *file)
+{
+	struct section *sec;
+	struct rela *rela;
+	struct instruction *insn;
+	bool found;
+
+	sec = find_section_by_name(file->elf, ".rela__unreachable");
+	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 .rela__unreachable");
+			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;
+	}
+
+	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;
+
+	list_for_each_entry(sec, &file->elf->sections, list) {
+		list_for_each_entry(func, &sec->symbol_list, list) {
+			if (func->type != STT_FUNC)
+				continue;
+
+			if (!ignore_func(file, func))
+				continue;
+
+			func_for_each_insn(file, func, insn)
+				insn->visited = 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_nospec_ignores(struct objtool_file *file)
+{
+	struct section *sec;
+	struct rela *rela;
+	struct instruction *insn;
+
+	sec = find_section_by_name(file->elf, ".rela.discard.nospec");
+	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.nospec 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 (insn->type != INSN_JUMP_CONDITIONAL &&
+		    insn->type != INSN_JUMP_UNCONDITIONAL)
+			continue;
+
+		/* skip ignores */
+		if (insn->visited)
+			continue;
+
+		rela = find_rela_by_dest_range(insn->sec, insn->offset,
+					       insn->len);
+		if (!rela) {
+			dest_sec = insn->sec;
+			dest_off = insn->offset + insn->len + insn->immediate;
+		} else if (rela->sym->type == STT_SECTION) {
+			dest_sec = rela->sym->sec;
+			dest_off = rela->addend + 4;
+		} else if (rela->sym->sec->idx) {
+			dest_sec = rela->sym->sec;
+			dest_off = rela->sym->sym.st_value + rela->addend + 4;
+		} else if (strstr(rela->sym->name, "_indirect_thunk_")) {
+			/*
+			 * Retpoline jumps are really dynamic jumps in
+			 * disguise, so convert them accordingly.
+			 */
+			insn->type = INSN_JUMP_DYNAMIC;
+			continue;
+		} else {
+			/* sibling call */
+			insn->jump_dest = 0;
+			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;
+		}
+	}
+
+	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(insn->sec, insn->offset,
+					       insn->len);
+		if (!rela) {
+			dest_off = insn->offset + insn->len + insn->immediate;
+			insn->call_dest = find_symbol_by_offset(insn->sec,
+								dest_off);
+			/*
+			 * FIXME: Thanks to retpolines, it's now considered
+			 * normal for a function to call within itself.  So
+			 * disable this warning for now.
+			 */
+#if 0
+			if (!insn->call_dest) {
+				WARN_FUNC("can't find call dest symbol at offset 0x%lx",
+					  insn->sec, insn->offset, dest_off);
+				return -1;
+			}
+#endif
+		} else if (rela->sym->type == STT_SECTION) {
+			insn->call_dest = find_symbol_by_offset(rela->sym->sec,
+								rela->addend+4);
+			if (!insn->call_dest ||
+			    insn->call_dest->type != STT_FUNC) {
+				WARN_FUNC("can't find call dest symbol at %s+0x%x",
+					  insn->sec, insn->offset,
+					  rela->sym->sec->name,
+					  rela->addend + 4);
+				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.
+ *
+ * 4. It has been requested that we don't validate the !POPCNT feature path
+ *    which is a "very very small percentage of machines".
+ */
+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;
+	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;
+
+		if (special_alt->skip_orig)
+			insn->type = INSN_NOP;
+
+		insn->alt_group = true;
+		last_orig_insn = insn;
+	}
+
+	if (!next_insn_same_sec(file, last_orig_insn)) {
+		WARN("%s: don't know how to handle alternatives at end of section",
+		     special_alt->orig_sec->name);
+		return -1;
+	}
+
+	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);
+	fake_jump->sec = special_alt->new_sec;
+	fake_jump->offset = -1;
+	fake_jump->type = INSN_JUMP_UNCONDITIONAL;
+	fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
+
+	if (!special_alt->new_len) {
+		*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;
+
+		if (insn->type != INSN_JUMP_CONDITIONAL &&
+		    insn->type != INSN_JUMP_UNCONDITIONAL)
+			continue;
+
+		if (!insn->immediate)
+			continue;
+
+		dest_off = insn->offset + insn->len + insn->immediate;
+		if (dest_off == special_alt->new_off + special_alt->new_len)
+			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;
+	}
+
+	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;
+		}
+
+		/* Ignore retpoline alternatives. */
+		if (orig_insn->ignore_alts)
+			continue;
+
+		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) {
+			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;
+		list_add_tail(&alt->list, &orig_insn->alts);
+
+		list_del(&special_alt->list);
+		free(special_alt);
+	}
+
+out:
+	return ret;
+}
+
+static int add_switch_table(struct objtool_file *file, struct symbol *func,
+			    struct instruction *insn, struct rela *table,
+			    struct rela *next_table)
+{
+	struct rela *rela = table;
+	struct instruction *alt_insn;
+	struct alternative *alt;
+
+	list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
+		if (rela == next_table)
+			break;
+
+		if (rela->sym->sec != insn->sec ||
+		    rela->addend <= func->offset ||
+		    rela->addend >= func->offset + func->len)
+			break;
+
+		alt_insn = find_insn(file, insn->sec, rela->addend);
+		if (!alt_insn) {
+			WARN("%s: can't find instruction at %s+0x%x",
+			     file->rodata->rela->name, insn->sec->name,
+			     rela->addend);
+			return -1;
+		}
+
+		alt = malloc(sizeof(*alt));
+		if (!alt) {
+			WARN("malloc failed");
+			return -1;
+		}
+
+		alt->insn = alt_insn;
+		list_add_tail(&alt->list, &insn->alts);
+	}
+
+	return 0;
+}
+
+/*
+ * find_switch_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.
+ *
+ *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
+ *    ensure the same register is used in the mov and jump instructions.
+ */
+static struct rela *find_switch_table(struct objtool_file *file,
+				      struct symbol *func,
+				      struct instruction *insn)
+{
+	struct rela *text_rela, *rodata_rela;
+	struct instruction *orig_insn = insn;
+
+	text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
+	if (text_rela && text_rela->sym == file->rodata->sym) {
+		/* case 1 */
+		rodata_rela = find_rela_by_dest(file->rodata,
+						text_rela->addend);
+		if (rodata_rela)
+			return rodata_rela;
+
+		/* case 2 */
+		rodata_rela = find_rela_by_dest(file->rodata,
+						text_rela->addend + 4);
+		if (!rodata_rela)
+			return NULL;
+		file->ignore_unreachables = true;
+		return rodata_rela;
+	}
+
+	/* case 3 */
+	func_for_each_insn_continue_reverse(file, func, insn) {
+		if (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(insn->sec, insn->offset,
+						    insn->len);
+		if (!text_rela || text_rela->sym != file->rodata->sym)
+			continue;
+
+		/*
+		 * Make sure the .rodata address isn't associated with a
+		 * symbol.  gcc jump tables are anonymous data.
+		 */
+		if (find_symbol_containing(file->rodata, text_rela->addend))
+			continue;
+
+		return find_rela_by_dest(file->rodata, text_rela->addend);
+	}
+
+	return NULL;
+}
+
+static int add_func_switch_tables(struct objtool_file *file,
+				  struct symbol *func)
+{
+	struct instruction *insn, *prev_jump = NULL;
+	struct rela *rela, *prev_rela = NULL;
+	int ret;
+
+	func_for_each_insn(file, func, insn) {
+		if (insn->type != INSN_JUMP_DYNAMIC)
+			continue;
+
+		rela = find_switch_table(file, func, insn);
+		if (!rela)
+			continue;
+
+		/*
+		 * We found a switch table, but we don't know yet how big it
+		 * is.  Don't add it until we reach the end of the function or
+		 * the beginning of another switch table in the same function.
+		 */
+		if (prev_jump) {
+			ret = add_switch_table(file, func, prev_jump, prev_rela,
+					       rela);
+			if (ret)
+				return ret;
+		}
+
+		prev_jump = insn;
+		prev_rela = rela;
+	}
+
+	if (prev_jump) {
+		ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
+		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_switch_table_alts(struct objtool_file *file)
+{
+	struct section *sec;
+	struct symbol *func;
+	int ret;
+
+	if (!file->rodata || !file->rodata->rela)
+		return 0;
+
+	list_for_each_entry(sec, &file->elf->sections, list) {
+		list_for_each_entry(func, &sec->symbol_list, list) {
+			if (func->type != STT_FUNC)
+				continue;
+
+			ret = add_func_switch_tables(file, func);
+			if (ret)
+				return ret;
+		}
+	}
+
+	return 0;
+}
+
+static int decode_sections(struct objtool_file *file)
+{
+	int ret;
+
+	ret = decode_instructions(file);
+	if (ret)
+		return ret;
+
+	ret = add_dead_ends(file);
+	if (ret)
+		return ret;
+
+	add_ignores(file);
+
+	ret = add_nospec_ignores(file);
+	if (ret)
+		return ret;
+
+	ret = add_jump_destinations(file);
+	if (ret)
+		return ret;
+
+	ret = add_call_destinations(file);
+	if (ret)
+		return ret;
+
+	ret = add_special_section_alts(file);
+	if (ret)
+		return ret;
+
+	ret = add_switch_table_alts(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 instruction *insn)
+{
+	return (insn->state & STATE_FP_SAVED) ||
+	       (insn->state & STATE_FP_SETUP);
+}
+
+static bool has_valid_stack_frame(struct instruction *insn)
+{
+	return (insn->state & STATE_FP_SAVED) &&
+	       (insn->state & STATE_FP_SETUP);
+}
+
+static unsigned int frame_state(unsigned long state)
+{
+	return (state & (STATE_FP_SAVED | STATE_FP_SETUP));
+}
+
+/*
+ * 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 instruction *first, unsigned char first_state)
+{
+	struct alternative *alt;
+	struct instruction *insn;
+	struct section *sec;
+	struct symbol *func = NULL;
+	unsigned char state;
+	int ret;
+
+	insn = first;
+	sec = insn->sec;
+	state = first_state;
+
+	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) {
+		if (file->c_file && insn->func) {
+			if (func && func != insn->func) {
+				WARN("%s() falls through to next function %s()",
+				     func->name, insn->func->name);
+				return 1;
+			}
+
+			func = insn->func;
+		}
+
+		if (insn->visited) {
+			if (frame_state(insn->state) != frame_state(state)) {
+				WARN_FUNC("frame pointer state mismatch",
+					  sec, insn->offset);
+				return 1;
+			}
+
+			return 0;
+		}
+
+		insn->visited = true;
+		insn->state = state;
+
+		list_for_each_entry(alt, &insn->alts, list) {
+			ret = validate_branch(file, alt->insn, state);
+			if (ret)
+				return 1;
+		}
+
+		switch (insn->type) {
+
+		case INSN_FP_SAVE:
+			if (!nofp) {
+				if (state & STATE_FP_SAVED) {
+					WARN_FUNC("duplicate frame pointer save",
+						  sec, insn->offset);
+					return 1;
+				}
+				state |= STATE_FP_SAVED;
+			}
+			break;
+
+		case INSN_FP_SETUP:
+			if (!nofp) {
+				if (state & STATE_FP_SETUP) {
+					WARN_FUNC("duplicate frame pointer setup",
+						  sec, insn->offset);
+					return 1;
+				}
+				state |= STATE_FP_SETUP;
+			}
+			break;
+
+		case INSN_FP_RESTORE:
+			if (!nofp) {
+				if (has_valid_stack_frame(insn))
+					state &= ~STATE_FP_SETUP;
+
+				state &= ~STATE_FP_SAVED;
+			}
+			break;
+
+		case INSN_RETURN:
+			if (!nofp && has_modified_stack_frame(insn)) {
+				WARN_FUNC("return without frame pointer restore",
+					  sec, insn->offset);
+				return 1;
+			}
+			return 0;
+
+		case INSN_CALL:
+			if (is_fentry_call(insn)) {
+				state |= STATE_FENTRY;
+				break;
+			}
+
+			ret = dead_end_function(file, insn->call_dest);
+			if (ret == 1)
+				return 0;
+			if (ret == -1)
+				return 1;
+
+			/* fallthrough */
+		case INSN_CALL_DYNAMIC:
+			if (!nofp && !has_valid_stack_frame(insn)) {
+				WARN_FUNC("call without frame pointer save/setup",
+					  sec, insn->offset);
+				return 1;
+			}
+			break;
+
+		case INSN_JUMP_CONDITIONAL:
+		case INSN_JUMP_UNCONDITIONAL:
+			if (insn->jump_dest) {
+				ret = validate_branch(file, insn->jump_dest,
+						      state);
+				if (ret)
+					return 1;
+			} else if (has_modified_stack_frame(insn)) {
+				WARN_FUNC("sibling call from callable instruction with changed frame pointer",
+					  sec, insn->offset);
+				return 1;
+			} /* else it's a sibling call */
+
+			if (insn->type == INSN_JUMP_UNCONDITIONAL)
+				return 0;
+
+			break;
+
+		case INSN_JUMP_DYNAMIC:
+			if (list_empty(&insn->alts) &&
+			    has_modified_stack_frame(insn)) {
+				WARN_FUNC("sibling call from callable instruction with changed frame pointer",
+					  sec, insn->offset);
+				return 1;
+			}
+
+			return 0;
+
+		default:
+			break;
+		}
+
+		if (insn->dead_end)
+			return 0;
+
+		insn = next_insn_same_sec(file, insn);
+		if (!insn) {
+			WARN("%s: unexpected end of section", sec->name);
+			return 1;
+		}
+	}
+
+	return 0;
+}
+
+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 symbol *func,
+				    struct instruction *insn)
+{
+	int i;
+
+	if (insn->type == INSN_NOP)
+		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 && insn->jump_dest) {
+			insn = insn->jump_dest;
+			continue;
+		}
+
+		if (insn->offset + insn->len >= func->offset + func->len)
+			break;
+		insn = list_next_entry(insn, list);
+	}
+
+	return false;
+}
+
+static int validate_functions(struct objtool_file *file)
+{
+	struct section *sec;
+	struct symbol *func;
+	struct instruction *insn;
+	int ret, warnings = 0;
+
+	list_for_each_entry(sec, &file->elf->sections, list) {
+		list_for_each_entry(func, &sec->symbol_list, list) {
+			if (func->type != STT_FUNC)
+				continue;
+
+			insn = find_insn(file, sec, func->offset);
+			if (!insn)
+				continue;
+
+			ret = validate_branch(file, insn, 0);
+			warnings += ret;
+		}
+	}
+
+	list_for_each_entry(sec, &file->elf->sections, list) {
+		list_for_each_entry(func, &sec->symbol_list, list) {
+			if (func->type != STT_FUNC)
+				continue;
+
+			func_for_each_insn(file, func, insn) {
+				if (insn->visited)
+					continue;
+
+				insn->visited = true;
+
+				if (file->ignore_unreachables || warnings ||
+				    ignore_unreachable_insn(func, insn))
+					continue;
+
+				/*
+				 * gcov produces a lot of unreachable
+				 * instructions.  If we get an unreachable
+				 * warning and the file has gcov enabled, just
+				 * ignore it, and all other such warnings for
+				 * the file.
+				 */
+				if (!file->ignore_unreachables &&
+				    gcov_enabled(file)) {
+					file->ignore_unreachables = true;
+					continue;
+				}
+
+				WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
+				warnings++;
+			}
+		}
+	}
+
+	return warnings;
+}
+
+static int validate_uncallable_instructions(struct objtool_file *file)
+{
+	struct instruction *insn;
+	int warnings = 0;
+
+	for_each_insn(file, insn) {
+		if (!insn->visited && insn->type == INSN_RETURN) {
+
+			/*
+			 * Don't warn about call instructions in unvisited
+			 * retpoline alternatives.
+			 */
+			if (!strcmp(insn->sec->name, ".altinstr_replacement"))
+				continue;
+
+			WARN_FUNC("return instruction outside of a callable function",
+				  insn->sec, insn->offset);
+			warnings++;
+		}
+	}
+
+	return warnings;
+}
+
+static void cleanup(struct objtool_file *file)
+{
+	struct instruction *insn, *tmpinsn;
+	struct alternative *alt, *tmpalt;
+
+	list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
+		list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
+			list_del(&alt->list);
+			free(alt);
+		}
+		list_del(&insn->list);
+		hash_del(&insn->hash);
+		free(insn);
+	}
+	elf_close(file->elf);
+}
+
+int check(const char *_objname, bool _nofp)
+{
+	struct objtool_file file;
+	int ret, warnings = 0;
+
+	objname = _objname;
+	nofp = _nofp;
+
+	file.elf = elf_open(objname);
+	if (!file.elf) {
+		fprintf(stderr, "error reading elf file %s\n", objname);
+		return 1;
+	}
+
+	INIT_LIST_HEAD(&file.insn_list);
+	hash_init(file.insn_hash);
+	file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
+	file.rodata = find_section_by_name(file.elf, ".rodata");
+	file.ignore_unreachables = false;
+	file.c_file = find_section_by_name(file.elf, ".comment");
+
+	ret = decode_sections(&file);
+	if (ret < 0)
+		goto out;
+	warnings += ret;
+
+	ret = validate_functions(&file);
+	if (ret < 0)
+		goto out;
+	warnings += ret;
+
+	ret = validate_uncallable_instructions(&file);
+	if (ret < 0)
+		goto out;
+	warnings += ret;
+
+out:
+	cleanup(&file);
+
+	/* ignore warnings for now until we get all the code cleaned up */
+	if (ret || warnings)
+		return 0;
+	return 0;
+}
diff --git a/tools/objtool/check.h b/tools/objtool/check.h
new file mode 100644
index 000000000000..aca248a049e0
--- /dev/null
+++ b/tools/objtool/check.h
@@ -0,0 +1,51 @@
+/*
+ * Copyright (C) 2017 Josh Poimboeuf jpoimboe@redhat.com
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see http://www.gnu.org/licenses/.
+ */
+
+#ifndef _CHECK_H
+#define _CHECK_H
+
+#include <stdbool.h>
+#include "elf.h"
+#include "arch.h"
+#include <linux/hashtable.h>
+
+struct instruction {
+	struct list_head list;
+	struct hlist_node hash;
+	struct section *sec;
+	unsigned long offset;
+	unsigned int len, state;
+	unsigned char type;
+	unsigned long immediate;
+	bool alt_group, visited, dead_end, ignore_alts;
+	struct symbol *call_dest;
+	struct instruction *jump_dest;
+	struct list_head alts;
+	struct symbol *func;
+};
+
+struct objtool_file {
+	struct elf *elf;
+	struct list_head insn_list;
+	DECLARE_HASHTABLE(insn_hash, 16);
+	struct section *rodata, *whitelist;
+	bool ignore_unreachables, c_file;
+};
+
+int check(const char *objname, bool nofp);
+
+#endif /* _CHECK_H */
-- 
2.17.1

    

2025

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2023

2022

2021

2020

2019

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[PATCH 02/29] objtool: Move checking code to check.c