1 files changed, 1072 insertions, 0 deletions

diff --git a/tools/objtool/builtin-check.c b/tools/objtool/builtin-check.c
new file mode 100644
index 000000000000..f7e0ebac3fbe
--- /dev/null
+++ b/tools/objtool/builtin-check.c
@@ -0,0 +1,1072 @@
+/*
+ * Copyright (C) 2015 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/>.
+ */
+
+/*
+ * objtool check:
+ *
+ * This command analyzes every .o file and ensures the validity of its stack
+ * trace metadata.  It enforces a set of rules on asm code and C inline
+ * assembly code so that stack traces can be reliable.
+ *
+ * For more information, see tools/objtool/Documentation/stack-validation.txt.
+ */
+
+#include <string.h>
+#include <subcmd/parse-options.h>
+
+#include "builtin.h"
+#include "elf.h"
+#include "special.h"
+#include "arch.h"
+#include "warn.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 section *sec;
+	unsigned long offset;
+	unsigned int len, state;
+	unsigned char type;
+	unsigned long immediate;
+	bool alt_group, visited;
+	struct symbol *call_dest;
+	struct instruction *jump_dest;
+	struct list_head alts;
+};
+
+struct alternative {
+	struct list_head list;
+	struct instruction *insn;
+};
+
+struct objtool_file {
+	struct elf *elf;
+	struct list_head insns;
+};
+
+const char *objname;
+static bool nofp;
+
+static struct instruction *find_instruction(struct objtool_file *file,
+					    struct section *sec,
+					    unsigned long offset)
+{
+	struct instruction *insn;
+
+	list_for_each_entry(insn, &file->insns, list)
+		if (insn->sec == sec && insn->offset == offset)
+			return insn;
+
+	return NULL;
+}
+
+/*
+ * 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 section *macro_sec;
+	struct rela *rela;
+	struct instruction *insn;
+
+	/* check for STACK_FRAME_NON_STANDARD */
+	macro_sec = find_section_by_name(file->elf, "__func_stack_frame_non_standard");
+	if (macro_sec && macro_sec->rela)
+		list_for_each_entry(rela, &macro_sec->rela->relas, list)
+			if (rela->sym->sec == func->sec &&
+			    rela->addend == func->offset)
+				return true;
+
+	/* check if it has a context switching instruction */
+	insn = find_instruction(file, func->sec, func->offset);
+	if (!insn)
+		return false;
+	list_for_each_entry_from(insn, &file->insns, list) {
+		if (insn->sec != func->sec ||
+		    insn->offset >= func->offset + func->len)
+			break;
+		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.
+ */
+static bool dead_end_function(struct objtool_file *file, struct symbol *func)
+{
+	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",
+		"__module_put_and_exit",
+		"complete_and_exit",
+		"kvm_spurious_fault",
+		"__reiserfs_panic",
+		"lbug_with_loc"
+	};
+
+	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->sec)
+		return false;
+
+	insn = find_instruction(file, func->sec, func->offset);
+	if (!insn)
+		return false;
+
+	list_for_each_entry_from(insn, &file->insns, list) {
+		if (insn->sec != func->sec ||
+		    insn->offset >= func->offset + func->len)
+			break;
+
+		empty = false;
+
+		if (insn->type == INSN_RETURN)
+			return false;
+
+		if (insn->type == INSN_JUMP_UNCONDITIONAL) {
+			struct instruction *dest = insn->jump_dest;
+			struct symbol *dest_func;
+
+			if (!dest)
+				/* sibling call to another file */
+				return false;
+
+			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;
+
+				return dead_end_function(file, dest_func);
+			}
+		}
+
+		if (insn->type == INSN_JUMP_DYNAMIC)
+			/* sibling call */
+			return false;
+	}
+
+	return !empty;
+}
+
+/*
+ * Call the arch-specific instruction decoder for all the instructions and add
+ * them to the global insns list.
+ */
+static int decode_instructions(struct objtool_file *file)
+{
+	struct section *sec;
+	unsigned long offset;
+	struct instruction *insn;
+	int ret;
+
+	INIT_LIST_HEAD(&file->insns);
+
+	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;
+			}
+
+			list_add_tail(&insn->list, &file->insns);
+		}
+	}
+
+	return 0;
+}
+
+/*
+ * Warnings shouldn't be reported for ignored functions.
+ */
+static void get_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->symbols, list) {
+			if (func->type != STT_FUNC)
+				continue;
+
+			if (!ignore_func(file, func))
+				continue;
+
+			insn = find_instruction(file, sec, func->offset);
+			if (!insn)
+				continue;
+
+			list_for_each_entry_from(insn, &file->insns, list) {
+				if (insn->sec != func->sec ||
+				    insn->offset >= func->offset + func->len)
+					break;
+
+				insn->visited = true;
+			}
+		}
+	}
+}
+
+/*
+ * Find the destination instructions for all jumps.
+ */
+static int get_jump_destinations(struct objtool_file *file)
+{
+	struct instruction *insn;
+	struct rela *rela;
+	struct section *dest_sec;
+	unsigned long dest_off;
+
+	list_for_each_entry(insn, &file->insns, list) {
+		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 {
+			/* sibling call */
+			insn->jump_dest = 0;
+			continue;
+		}
+
+		insn->jump_dest = find_instruction(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 get_call_destinations(struct objtool_file *file)
+{
+	struct instruction *insn;
+	unsigned long dest_off;
+	struct rela *rela;
+
+	list_for_each_entry(insn, &file->insns, list) {
+		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);
+			if (!insn->call_dest) {
+				WARN_FUNC("can't find call dest symbol at offset 0x%lx",
+					  insn->sec, insn->offset, dest_off);
+				return -1;
+			}
+		} 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;
+	list_for_each_entry_from(insn, &file->insns, list) {
+		if (insn->sec != special_alt->orig_sec ||
+		    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 (list_is_last(&last_orig_insn->list, &file->insns) ||
+	    list_next_entry(last_orig_insn, list)->sec != special_alt->orig_sec) {
+		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;
+	list_for_each_entry_from(insn, &file->insns, list) {
+		if (insn->sec != special_alt->new_sec ||
+		    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 get_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) {
+		alt = malloc(sizeof(*alt));
+		if (!alt) {
+			WARN("malloc failed");
+			ret = -1;
+			goto out;
+		}
+
+		orig_insn = find_instruction(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_instruction(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->insn = new_insn;
+		list_add_tail(&alt->list, &orig_insn->alts);
+
+		list_del(&special_alt->list);
+		free(special_alt);
+	}
+
+out:
+	return ret;
+}
+
+/*
+ * 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 get_switch_alts(struct objtool_file *file)
+{
+	struct instruction *insn, *alt_insn;
+	struct rela *rodata_rela, *rela;
+	struct section *rodata;
+	struct symbol *func;
+	struct alternative *alt;
+
+	list_for_each_entry(insn, &file->insns, list) {
+		if (insn->type != INSN_JUMP_DYNAMIC)
+			continue;
+
+		rodata_rela = find_rela_by_dest_range(insn->sec, insn->offset,
+						      insn->len);
+		if (!rodata_rela || strcmp(rodata_rela->sym->name, ".rodata"))
+			continue;
+
+		rodata = find_section_by_name(file->elf, ".rodata");
+		if (!rodata || !rodata->rela)
+			continue;
+
+		/* common case: jmpq *[addr](,%rax,8) */
+		rela = find_rela_by_dest(rodata, rodata_rela->addend);
+
+		/* rare case:   jmpq *[addr](%rip) */
+		if (!rela)
+			rela = find_rela_by_dest(rodata,
+						 rodata_rela->addend + 4);
+		if (!rela)
+			continue;
+
+		func = find_containing_func(insn->sec, insn->offset);
+		if (!func) {
+			WARN_FUNC("can't find containing func",
+				  insn->sec, insn->offset);
+			return -1;
+		}
+
+		list_for_each_entry_from(rela, &rodata->rela->relas, list) {
+			if (rela->sym->sec != insn->sec ||
+			    rela->addend <= func->offset ||
+			    rela->addend >= func->offset + func->len)
+				break;
+
+			alt_insn = find_instruction(file, insn->sec,
+						    rela->addend);
+			if (!alt_insn) {
+				WARN("%s: can't find instruction at %s+0x%x",
+				     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;
+}
+
+static int decode_sections(struct objtool_file *file)
+{
+	int ret;
+
+	ret = decode_instructions(file);
+	if (ret)
+		return ret;
+
+	get_ignores(file);
+
+	ret = get_jump_destinations(file);
+	if (ret)
+		return ret;
+
+	ret = get_call_destinations(file);
+	if (ret)
+		return ret;
+
+	ret = get_special_section_alts(file);
+	if (ret)
+		return ret;
+
+	ret = get_switch_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);
+}
+
+/*
+ * 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;
+	unsigned char state;
+	int ret, warnings = 0;
+
+	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);
+		warnings++;
+	}
+
+	while (1) {
+		if (insn->visited) {
+			if (insn->state != state) {
+				WARN_FUNC("frame pointer state mismatch",
+					  sec, insn->offset);
+				warnings++;
+			}
+
+			return warnings;
+		}
+
+		/*
+		 * Catch a rare case where a noreturn function falls through to
+		 * the next function.
+		 */
+		if (is_fentry_call(insn) && (state & STATE_FENTRY))
+			return warnings;
+
+		insn->visited = true;
+		insn->state = state;
+
+		list_for_each_entry(alt, &insn->alts, list) {
+			ret = validate_branch(file, alt->insn, state);
+			warnings += ret;
+		}
+
+		switch (insn->type) {
+
+		case INSN_FP_SAVE:
+			if (!nofp) {
+				if (state & STATE_FP_SAVED) {
+					WARN_FUNC("duplicate frame pointer save",
+						  sec, insn->offset);
+					warnings++;
+				}
+				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);
+					warnings++;
+				}
+				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);
+				warnings++;
+			}
+			return warnings;
+
+		case INSN_CALL:
+			if (is_fentry_call(insn)) {
+				state |= STATE_FENTRY;
+				break;
+			}
+
+			if (dead_end_function(file, insn->call_dest))
+				return warnings;
+
+			/* fallthrough */
+		case INSN_CALL_DYNAMIC:
+			if (!nofp && !has_valid_stack_frame(insn)) {
+				WARN_FUNC("call without frame pointer save/setup",
+					  sec, insn->offset);
+				warnings++;
+			}
+			break;
+
+		case INSN_JUMP_CONDITIONAL:
+		case INSN_JUMP_UNCONDITIONAL:
+			if (insn->jump_dest) {
+				ret = validate_branch(file, insn->jump_dest,
+						      state);
+				warnings += ret;
+			} else if (has_modified_stack_frame(insn)) {
+				WARN_FUNC("sibling call from callable instruction with changed frame pointer",
+					  sec, insn->offset);
+				warnings++;
+			} /* else it's a sibling call */
+
+			if (insn->type == INSN_JUMP_UNCONDITIONAL)
+				return warnings;
+
+			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);
+				warnings++;
+			}
+
+			return warnings;
+
+		case INSN_BUG:
+			return warnings;
+
+		default:
+			break;
+		}
+
+		insn = list_next_entry(insn, list);
+
+		if (&insn->list == &file->insns || insn->sec != sec) {
+			WARN("%s: unexpected end of section", sec->name);
+			warnings++;
+			return warnings;
+		}
+	}
+
+	return warnings;
+}
+
+static bool is_gcov_insn(struct instruction *insn)
+{
+	struct rela *rela;
+	struct section *sec;
+	struct symbol *sym;
+	unsigned long offset;
+
+	rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
+	if (!rela)
+		return false;
+
+	if (rela->sym->type != STT_SECTION)
+		return false;
+
+	sec = rela->sym->sec;
+	offset = rela->addend + insn->offset + insn->len - rela->offset;
+
+	list_for_each_entry(sym, &sec->symbols, list) {
+		if (sym->type != STT_OBJECT)
+			continue;
+
+		if (offset >= sym->offset && offset < sym->offset + sym->len)
+			return (!memcmp(sym->name, "__gcov0.", 8));
+	}
+
+	return false;
+}
+
+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,
+				    unsigned long func_end)
+{
+	int i;
+
+	if (insn->type == INSN_NOP)
+		return true;
+
+	if (is_gcov_insn(insn))
+		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_end)
+			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;
+	unsigned long func_end;
+	int ret, warnings = 0;
+
+	list_for_each_entry(sec, &file->elf->sections, list) {
+		list_for_each_entry(func, &sec->symbols, list) {
+			if (func->type != STT_FUNC)
+				continue;
+
+			insn = find_instruction(file, sec, func->offset);
+			if (!insn) {
+				WARN("%s(): can't find starting instruction",
+				     func->name);
+				warnings++;
+				continue;
+			}
+
+			ret = validate_branch(file, insn, 0);
+			warnings += ret;
+		}
+	}
+
+	list_for_each_entry(sec, &file->elf->sections, list) {
+		list_for_each_entry(func, &sec->symbols, list) {
+			if (func->type != STT_FUNC)
+				continue;
+
+			insn = find_instruction(file, sec, func->offset);
+			if (!insn)
+				continue;
+
+			func_end = func->offset + func->len;
+
+			list_for_each_entry_from(insn, &file->insns, list) {
+				if (insn->sec != func->sec ||
+				    insn->offset >= func_end)
+					break;
+
+				if (insn->visited)
+					continue;
+
+				if (!ignore_unreachable_insn(insn, func_end)) {
+					WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
+					warnings++;
+				}
+
+				insn->visited = true;
+			}
+		}
+	}
+
+	return warnings;
+}
+
+static int validate_uncallable_instructions(struct objtool_file *file)
+{
+	struct instruction *insn;
+	int warnings = 0;
+
+	list_for_each_entry(insn, &file->insns, list) {
+		if (!insn->visited && insn->type == INSN_RETURN) {
+			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->insns, list) {
+		list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
+			list_del(&alt->list);
+			free(alt);
+		}
+		list_del(&insn->list);
+		free(insn);
+	}
+	elf_close(file->elf);
+}
+
+const char * const check_usage[] = {
+	"objtool check [<options>] file.o",
+	NULL,
+};
+
+int cmd_check(int argc, const char **argv)
+{
+	struct objtool_file file;
+	int ret, warnings = 0;
+
+	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);
+
+	if (argc != 1)
+		usage_with_options(check_usage, 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.insns);
+
+	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;
+}