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Commit 13810435 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Ingo Molnar
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objtool: Support GCC 8's cold subfunctions 



GCC 8 moves a lot of unlikely code out of line to "cold" subfunctions in
.text.unlikely.  Properly detect the new subfunctions and treat them as
extensions of the original functions.

This fixes a bunch of warnings like:

  kernel/cgroup/cgroup.o: warning: objtool: parse_cgroup_root_flags()+0x33: sibling call from callable instruction with modified stack frame
  kernel/cgroup/cgroup.o: warning: objtool: cgroup_addrm_files()+0x290: sibling call from callable instruction with modified stack frame
  kernel/cgroup/cgroup.o: warning: objtool: cgroup_apply_control_enable()+0x25b: sibling call from callable instruction with modified stack frame
  kernel/cgroup/cgroup.o: warning: objtool: rebind_subsystems()+0x325: sibling call from callable instruction with modified stack frame

Reported-and-tested-by: default avatardamian <damian.tometzki@icloud.com>
Reported-by: default avatarArnd Bergmann <arnd@arndb.de>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: David Laight <David.Laight@ACULAB.COM>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/0965e7fcfc5f31a276f0c7f298ff770c19b68706.1525923412.git.jpoimboe@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 0afd0d9e

tools/objtool/check.c

+51 −42
Original line number Diff line number Diff line
@@ -59,6 +59,31 @@ static struct instruction *next_insn_same_sec(struct objtool_file *file, 
	return next;

}



static struct instruction *next_insn_same_func(struct objtool_file *file,

					       struct instruction *insn)

{

	struct instruction *next = list_next_entry(insn, list);

	struct symbol *func = insn->func;



	if (!func)

		return NULL;



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

		return next;



	/* Check if we're already in the subfunction: */

	if (func == func->cfunc)

		return NULL;



	/* Move to the subfunction: */

	return find_insn(file, func->cfunc->sec, func->cfunc->offset);

}



#define func_for_each_insn_all(file, func, insn)			\

	for (insn = find_insn(file, func->sec, func->offset);		\

	     insn;							\

	     insn = next_insn_same_func(file, insn))



#define func_for_each_insn(file, func, insn)				\

	for (insn = find_insn(file, func->sec, func->offset);		\

	     insn && &insn->list != &file->insn_list &&			\
@@ -149,10 +174,14 @@ static int __dead_end_function(struct objtool_file *file, struct symbol *func, 
			if (!strcmp(func->name, global_noreturns[i]))

				return 1;



	if (!func->sec)

	if (!func->len)

		return 0;



	func_for_each_insn(file, func, insn) {

	insn = find_insn(file, func->sec, func->offset);

	if (!insn->func)

		return 0;



	func_for_each_insn_all(file, func, insn) {

		empty = false;



		if (insn->type == INSN_RETURN)
@@ -167,28 +196,17 @@ static int __dead_end_function(struct objtool_file *file, struct symbol *func, 
	 * 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;



	func_for_each_insn_all(file, func, insn) {

		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 (dest->func && dest->func->pfunc != insn->func->pfunc) {



				/* local sibling call */

				if (recursion == 5) {

					/*

					 * Infinite recursion: two functions
@@ -199,7 +217,7 @@ static int __dead_end_function(struct objtool_file *file, struct symbol *func, 
					return 0;

				}



				return __dead_end_function(file, dest_func,

				return __dead_end_function(file, dest->func,

							   recursion + 1);

			}

		}
@@ -426,7 +444,7 @@ static void add_ignores(struct objtool_file *file) 
			if (!ignore_func(file, func))

				continue;



			func_for_each_insn(file, func, insn)

			func_for_each_insn_all(file, func, insn)

				insn->ignore = true;

		}

	}
@@ -786,9 +804,8 @@ static int add_special_section_alts(struct objtool_file *file) 
	return ret;

}



static int add_switch_table(struct objtool_file *file, struct symbol *func,

			    struct instruction *insn, struct rela *table,

			    struct rela *next_table)

static int add_switch_table(struct objtool_file *file, struct instruction *insn,

			    struct rela *table, struct rela *next_table)

{

	struct rela *rela = table;

	struct instruction *alt_insn;
@@ -798,18 +815,13 @@ static int add_switch_table(struct objtool_file *file, struct symbol *func, 
		if (rela == next_table)

			break;



		if (rela->sym->sec != insn->sec ||

		    rela->addend <= func->offset ||

		    rela->addend >= func->offset + func->len)

		alt_insn = find_insn(file, rela->sym->sec, rela->addend);

		if (!alt_insn)

			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;

		}

		/* Make sure the jmp dest is in the function or subfunction: */

		if (alt_insn->func->pfunc != insn->func->pfunc)

			break;



		alt = malloc(sizeof(*alt));

		if (!alt) {
@@ -947,7 +959,7 @@ static int add_func_switch_tables(struct objtool_file *file, 
	struct rela *rela, *prev_rela = NULL;

	int ret;



	func_for_each_insn(file, func, insn) {

	func_for_each_insn_all(file, func, insn) {

		if (!last)

			last = insn;
@@ -978,8 +990,7 @@ static int add_func_switch_tables(struct objtool_file *file, 
		 * the beginning of another switch table in the same function.

		 */

		if (prev_jump) {

			ret = add_switch_table(file, func, prev_jump, prev_rela,

					       rela);

			ret = add_switch_table(file, prev_jump, prev_rela, rela);

			if (ret)

				return ret;

		}
@@ -989,7 +1000,7 @@ static int add_func_switch_tables(struct objtool_file *file, 
	}



	if (prev_jump) {

		ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);

		ret = add_switch_table(file, prev_jump, prev_rela, NULL);

		if (ret)

			return ret;

	}
@@ -1753,15 +1764,13 @@ static int validate_branch(struct objtool_file *file, struct instruction *first, 
	while (1) {

		next_insn = next_insn_same_sec(file, insn);





		if (file->c_file && func && insn->func && func != insn->func) {

		if (file->c_file && func && insn->func && func != insn->func->pfunc) {

			WARN("%s() falls through to next function %s()",

			     func->name, insn->func->name);

			return 1;

		}



		if (insn->func)

			func = insn->func;

		func = insn->func ? insn->func->pfunc : NULL;



		if (func && insn->ignore) {

			WARN_FUNC("BUG: why am I validating an ignored function?",
@@ -1782,7 +1791,7 @@ static int validate_branch(struct objtool_file *file, struct instruction *first, 


				i = insn;

				save_insn = NULL;

				func_for_each_insn_continue_reverse(file, func, i) {

				func_for_each_insn_continue_reverse(file, insn->func, i) {

					if (i->save) {

						save_insn = i;

						break;
@@ -1869,7 +1878,7 @@ static int validate_branch(struct objtool_file *file, struct instruction *first, 
		case INSN_JUMP_UNCONDITIONAL:

			if (insn->jump_dest &&

			    (!func || !insn->jump_dest->func ||

			     func == insn->jump_dest->func)) {

			     insn->jump_dest->func->pfunc == func)) {

				ret = validate_branch(file, insn->jump_dest,

						      state);

				if (ret)
@@ -2064,7 +2073,7 @@ static int validate_functions(struct objtool_file *file) 


	for_each_sec(file, sec) {

		list_for_each_entry(func, &sec->symbol_list, list) {

			if (func->type != STT_FUNC)

			if (func->type != STT_FUNC || func->pfunc != func)

				continue;



			insn = find_insn(file, sec, func->offset);

tools/objtool/elf.c

+40 −2
Original line number Diff line number Diff line
@@ -79,6 +79,19 @@ struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset) 
	return NULL;

}



struct symbol *find_symbol_by_name(struct elf *elf, const char *name)

{

	struct section *sec;

	struct symbol *sym;



	list_for_each_entry(sec, &elf->sections, list)

		list_for_each_entry(sym, &sec->symbol_list, list)

			if (!strcmp(sym->name, name))

				return sym;



	return NULL;

}



struct symbol *find_symbol_containing(struct section *sec, unsigned long offset)

{

	struct symbol *sym;
@@ -203,10 +216,11 @@ static int read_sections(struct elf *elf) 


static int read_symbols(struct elf *elf)

{

	struct section *symtab;

	struct symbol *sym;

	struct section *symtab, *sec;

	struct symbol *sym, *pfunc;

	struct list_head *entry, *tmp;

	int symbols_nr, i;

	char *coldstr;



	symtab = find_section_by_name(elf, ".symtab");

	if (!symtab) {
@@ -281,6 +295,30 @@ static int read_symbols(struct elf *elf) 
		hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);

	}



	/* Create parent/child links for any cold subfunctions */

	list_for_each_entry(sec, &elf->sections, list) {

		list_for_each_entry(sym, &sec->symbol_list, list) {

			if (sym->type != STT_FUNC)

				continue;

			sym->pfunc = sym->cfunc = sym;

			coldstr = strstr(sym->name, ".cold.");

			if (coldstr) {

				coldstr[0] = '\0';

				pfunc = find_symbol_by_name(elf, sym->name);

				coldstr[0] = '.';



				if (!pfunc) {

					WARN("%s(): can't find parent function",

					     sym->name);

					goto err;

				}



				sym->pfunc = pfunc;

				pfunc->cfunc = sym;

			}

		}

	}



	return 0;



err:

tools/objtool/elf.h

+2 −0
Original line number Diff line number Diff line
@@ -61,6 +61,7 @@ struct symbol { 
	unsigned char bind, type;

	unsigned long offset;

	unsigned int len;

	struct symbol *pfunc, *cfunc;

};



struct rela {
@@ -86,6 +87,7 @@ struct elf { 
struct elf *elf_open(const char *name, int flags);

struct section *find_section_by_name(struct elf *elf, const char *name);

struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset);

struct symbol *find_symbol_by_name(struct elf *elf, const char *name);

struct symbol *find_symbol_containing(struct section *sec, unsigned long offset);

struct rela *find_rela_by_dest(struct section *sec, unsigned long offset);

struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,