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Commit 867ac9d7 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Ingo Molnar
Browse files

objtool: Fix gcov check for older versions of GCC 



Objtool tries to silence 'unreachable instruction' warnings when it
detects gcov is enabled, because gcov produces a lot of unreachable
instructions and they don't really matter.

However, the 0-day bot is still reporting some unreachable instruction
warnings with CONFIG_GCOV_KERNEL=y on GCC 4.6.4.

As it turns out, objtool's gcov detection doesn't work with older
versions of GCC because they don't create a bunch of symbols with the
'gcov.' prefix like newer versions of GCC do.

Move the gcov check out of objtool and instead just create a new
'--no-unreachable' flag which can be passed in by the kernel Makefile
when CONFIG_GCOV_KERNEL is defined.

Also rename the 'nofp' variable to 'no_fp' for consistency with the new
'no_unreachable' variable.

Reported-by: default avatarkbuild test robot <fengguang.wu@intel.com>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 9cfffb11 ("objtool: Skip all "unreachable instruction" warnings for gcov kernels")
Link: http://lkml.kernel.org/r/c243dc78eb2ffdabb6e927844dea39b6033cd395.1500939244.git.jpoimboe@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 9683a64f

scripts/Makefile.build

+3 −0
Original line number Diff line number Diff line
@@ -262,6 +262,9 @@ objtool_args = check 
ifndef CONFIG_FRAME_POINTER

objtool_args += --no-fp

endif

ifdef CONFIG_GCOV_KERNEL

objtool_args += --no-unreachable

endif



# 'OBJECT_FILES_NON_STANDARD := y': skip objtool checking for a directory

# 'OBJECT_FILES_NON_STANDARD_foo.o := 'y': skip objtool checking for a file

tools/objtool/builtin-check.c

+4 −3
Original line number Diff line number Diff line
@@ -29,7 +29,7 @@ 
#include "builtin.h"

#include "check.h"



bool nofp;

bool no_fp, no_unreachable;



static const char * const check_usage[] = {

	"objtool check [<options>] file.o",
@@ -37,7 +37,8 @@ static const char * const check_usage[] = { 
};



const struct option check_options[] = {

	OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),

	OPT_BOOLEAN('f', "no-fp", &no_fp, "Skip frame pointer validation"),

	OPT_BOOLEAN('u', "no-unreachable", &no_unreachable, "Skip 'unreachable instruction' warnings"),

	OPT_END(),

};
@@ -52,5 +53,5 @@ int cmd_check(int argc, const char **argv) 


	objname = argv[0];



	return check(objname, nofp, false);

	return check(objname, no_fp, no_unreachable, false);

}

tools/objtool/builtin-orc.c

+2 −2
Original line number Diff line number Diff line
@@ -37,7 +37,7 @@ static const char *orc_usage[] = { 
};



extern const struct option check_options[];

extern bool nofp;

extern bool no_fp, no_unreachable;



int cmd_orc(int argc, const char **argv)

{
@@ -51,7 +51,7 @@ int cmd_orc(int argc, const char **argv) 


		objname = argv[0];



		return check(objname, nofp, true);

		return check(objname, no_fp, no_unreachable, true);



	}

tools/objtool/check.c

+7 −29
Original line number Diff line number Diff line
@@ -33,7 +33,7 @@ struct alternative { 
};



const char *objname;

static bool nofp;

static bool no_fp;

struct cfi_state initial_func_cfi;



struct instruction *find_insn(struct objtool_file *file,
@@ -59,19 +59,6 @@ static struct instruction *next_insn_same_sec(struct objtool_file *file, 
	return next;

}



static bool gcov_enabled(struct objtool_file *file)

{

	struct section *sec;

	struct symbol *sym;



	for_each_sec(file, sec)

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

			if (!strncmp(sym->name, "__gcov_.", 8))

				return true;



	return false;

}



#define func_for_each_insn(file, func, insn)				\

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

	     insn && &insn->list != &file->insn_list &&			\
@@ -1174,7 +1161,7 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state) 
				regs[CFI_BP].base = CFI_BP;

				regs[CFI_BP].offset = -state->stack_size;

				state->bp_scratch = false;

			} else if (!nofp) {

			} else if (!no_fp) {



				WARN_FUNC("unknown stack-related register move",

					  insn->sec, insn->offset);
@@ -1345,7 +1332,7 @@ static int update_insn_state(struct instruction *insn, struct insn_state *state) 
		}



		/* detect when asm code uses rbp as a scratch register */

		if (!nofp && insn->func && op->src.reg == CFI_BP &&

		if (!no_fp && insn->func && op->src.reg == CFI_BP &&

		    cfa->base != CFI_BP)

			state->bp_scratch = true;

		break;
@@ -1593,7 +1580,7 @@ static int validate_branch(struct objtool_file *file, struct instruction *first, 


			/* fallthrough */

		case INSN_CALL_DYNAMIC:

			if (!nofp && func && !has_valid_stack_frame(&state)) {

			if (!no_fp && func && !has_valid_stack_frame(&state)) {

				WARN_FUNC("call without frame pointer save/setup",

					  sec, insn->offset);

				return 1;
@@ -1779,15 +1766,6 @@ static int validate_reachable_instructions(struct objtool_file *file) 
		if (insn->visited || ignore_unreachable_insn(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.  Do

		 * this here because this is an expensive function.

		 */

		if (gcov_enabled(file))

			return 0;



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

		return 1;

	}
@@ -1812,13 +1790,13 @@ static void cleanup(struct objtool_file *file) 
	elf_close(file->elf);

}



int check(const char *_objname, bool _nofp, bool orc)

int check(const char *_objname, bool _no_fp, bool no_unreachable, bool orc)

{

	struct objtool_file file;

	int ret, warnings = 0;



	objname = _objname;

	nofp = _nofp;

	no_fp = _no_fp;



	file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY);

	if (!file.elf)
@@ -1829,7 +1807,7 @@ int check(const char *_objname, bool _nofp, bool orc) 
	file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");

	file.rodata = find_section_by_name(file.elf, ".rodata");

	file.c_file = find_section_by_name(file.elf, ".comment");

	file.ignore_unreachables = false;

	file.ignore_unreachables = no_unreachable;

	file.hints = false;



	arch_initial_func_cfi_state(&initial_func_cfi);

tools/objtool/check.h

+1 −1
Original line number Diff line number Diff line
@@ -61,7 +61,7 @@ struct objtool_file { 
	bool ignore_unreachables, c_file, hints;

};



int check(const char *objname, bool nofp, bool orc);

int check(const char *objname, bool no_fp, bool no_unreachable, bool orc);



struct instruction *find_insn(struct objtool_file *file,

			      struct section *sec, unsigned long offset);