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Commit bbda5ec6 authored by Masahiro Yamada's avatar Masahiro Yamada
Browse files

kbuild: simplify dependency generation for CONFIG_TRIM_UNUSED_KSYMS 



My main motivation of this commit is to clean up scripts/Kbuild.include
and scripts/Makefile.build.

Currently, CONFIG_TRIM_UNUSED_KSYMS works with a tricky gimmick;
possibly exported symbols are detected by letting $(CPP) replace
EXPORT_SYMBOL* with a special string '=== __KSYM_*===', which is
post-processed by sed, and passed to fixdep. The extra preprocessing
is costly, and hacking cmd_and_fixdep is ugly.

I came up with a new way to find exported symbols; insert a dummy
symbol __ksym_marker_* to each potentially exported symbol. Those
dummy symbols are picked up by $(NM), post-processed by sed, then
appended to .*.cmd files. I collected the post-process part to a
new shell script scripts/gen_ksymdeps.sh for readability. The dummy
symbols are put into the .discard.* section so that the linker
script rips them off the final vmlinux or modules.

A nice side-effect is building with CONFIG_TRIM_UNUSED_KSYMS will
be much faster.

Signed-off-by: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: default avatarNicolas Pitre <nico@linaro.org>
parent ee3e46b7

include/asm-generic/export.h

+8 −5
Original line number Diff line number Diff line
@@ -59,16 +59,19 @@ __kcrctab_\name: 
.endm

#undef __put



#if defined(__KSYM_DEPS__)



#define __EXPORT_SYMBOL(sym, val, sec)	=== __KSYM_##sym ===



#elif defined(CONFIG_TRIM_UNUSED_KSYMS)

#if defined(CONFIG_TRIM_UNUSED_KSYMS)



#include <linux/kconfig.h>

#include <generated/autoksyms.h>



.macro __ksym_marker sym

	.section ".discard.ksym","a"

__ksym_marker_\sym:

	 .previous

.endm



#define __EXPORT_SYMBOL(sym, val, sec)				\

	__ksym_marker sym;					\

	__cond_export_sym(sym, val, sec, __is_defined(__KSYM_##sym))

#define __cond_export_sym(sym, val, sec, conf)			\

	___cond_export_sym(sym, val, sec, conf)

include/linux/export.h

+9 −9
Original line number Diff line number Diff line
@@ -92,22 +92,22 @@ struct kernel_symbol { 
 */

#define __EXPORT_SYMBOL(sym, sec)



#elif defined(__KSYM_DEPS__)

#elif defined(CONFIG_TRIM_UNUSED_KSYMS)



#include <generated/autoksyms.h>



/*

 * For fine grained build dependencies, we want to tell the build system

 * about each possible exported symbol even if they're not actually exported.

 * We use a string pattern that is unlikely to be valid code that the build

 * system filters out from the preprocessor output (see ksym_dep_filter

 * in scripts/Kbuild.include).

 * We use a symbol pattern __ksym_marker_<symbol> that the build system filters

 * from the $(NM) output (see scripts/gen_ksymdeps.sh). These symbols are

 * discarded in the final link stage.

 */

#define __EXPORT_SYMBOL(sym, sec)	=== __KSYM_##sym ===



#elif defined(CONFIG_TRIM_UNUSED_KSYMS)



#include <generated/autoksyms.h>

#define __ksym_marker(sym)	\

	static int __ksym_marker_##sym[0] __section(".discard.ksym") __used



#define __EXPORT_SYMBOL(sym, sec)				\

	__ksym_marker(sym);					\

	__cond_export_sym(sym, sec, __is_defined(__KSYM_##sym))

#define __cond_export_sym(sym, sec, conf)			\

	___cond_export_sym(sym, sec, conf)

scripts/Kbuild.include

+0 −28
Original line number Diff line number Diff line
@@ -260,39 +260,11 @@ if_changed_dep = $(if $(strip $(any-prereq) $(arg-check) ), \ 
	@set -e;                                                             \

	$(cmd_and_fixdep), @:)



ifndef CONFIG_TRIM_UNUSED_KSYMS



cmd_and_fixdep =                                                             \

	$(echo-cmd) $(cmd_$(1));                                             \

	scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).cmd;\

	rm -f $(depfile);



else



# Filter out exported kernel symbol names from the preprocessor output.

# See also __KSYM_DEPS__ in include/linux/export.h.

# We disable the depfile generation here, so as not to overwrite the existing

# depfile while fixdep is parsing it.

flags_nodeps = $(filter-out -Wp$(comma)-M%, $($(1)))

ksym_dep_filter =                                                            \

	case "$(1)" in                                                       \

	  cc_*_c|cpp_i_c)                                                    \

	    $(CPP) $(call flags_nodeps,c_flags) -D__KSYM_DEPS__ $< ;;        \

	  as_*_S|cpp_s_S)                                                    \

	    $(CPP) $(call flags_nodeps,a_flags) -D__KSYM_DEPS__ $< ;;        \

	  boot*|build*|cpp_its_S|*cpp_lds_S|dtc|host*|vdso*) : ;;            \

	  *) echo "Don't know how to preprocess $(1)" >&2; false ;;          \

	esac | tr ";" "\n" | sed -n 's/^.*=== __KSYM_\(.*\) ===.*$$/_\1/p'



cmd_and_fixdep =                                                             \

	$(echo-cmd) $(cmd_$(1));                                             \

	$(ksym_dep_filter) |                                                 \

		scripts/basic/fixdep -e $(depfile) $@ '$(make-cmd)'          \

			> $(dot-target).cmd;	                             \

	rm -f $(depfile);



endif



# Usage: $(call if_changed_rule,foo)

# Will check if $(cmd_foo) or any of the prerequisites changed,

# and if so will execute $(rule_foo).

scripts/Makefile.build

+7 −0
Original line number Diff line number Diff line
@@ -254,9 +254,15 @@ objtool_dep = $(objtool_obj) \ 
	      $(wildcard include/config/orc/unwinder.h		\

			 include/config/stack/validation.h)



ifdef CONFIG_TRIM_UNUSED_KSYMS

cmd_gen_ksymdeps = \

	$(CONFIG_SHELL) $(srctree)/scripts/gen_ksymdeps.sh $@ >> $(dot-target).cmd;

endif



define rule_cc_o_c

	$(call echo-cmd,checksrc) $(cmd_checksrc)			  \

	$(call cmd_and_fixdep,cc_o_c)					  \

	$(cmd_gen_ksymdeps)						  \

	$(cmd_checkdoc)							  \

	$(call echo-cmd,objtool) $(cmd_objtool)				  \

	$(cmd_modversions_c)						  \
@@ -265,6 +271,7 @@ endef 


define rule_as_o_S

	$(call cmd_and_fixdep,as_o_S)					  \

	$(cmd_gen_ksymdeps)						  \

	$(call echo-cmd,objtool) $(cmd_objtool)				  \

	$(cmd_modversions_S)

endef

scripts/basic/fixdep.c

+4 −27
Original line number Diff line number Diff line
@@ -105,8 +105,7 @@ 


static void usage(void)

{

	fprintf(stderr, "Usage: fixdep [-e] <depfile> <target> <cmdline>\n");

	fprintf(stderr, " -e  insert extra dependencies given on stdin\n");

	fprintf(stderr, "Usage: fixdep <depfile> <target> <cmdline>\n");

	exit(1);

}
@@ -131,21 +130,6 @@ static void print_dep(const char *m, int slen, const char *dir) 
	printf(".h) \\\n");

}



static void do_extra_deps(void)

{

	char buf[80];



	while (fgets(buf, sizeof(buf), stdin)) {

		int len = strlen(buf);



		if (len < 2 || buf[len - 1] != '\n') {

			fprintf(stderr, "fixdep: bad data on stdin\n");

			exit(1);

		}

		print_dep(buf, len - 1, "include/ksym");

	}

}



struct item {

	struct item	*next;

	unsigned int	len;
@@ -293,7 +277,7 @@ static int is_ignored_file(const char *s, int len) 
 * assignments are parsed not only by make, but also by the rather simple

 * parser in scripts/mod/sumversion.c.

 */

static void parse_dep_file(char *m, const char *target, int insert_extra_deps)

static void parse_dep_file(char *m, const char *target)

{

	char *p;

	int is_last, is_target;
@@ -369,9 +353,6 @@ static void parse_dep_file(char *m, const char *target, int insert_extra_deps) 
		exit(1);

	}



	if (insert_extra_deps)

		do_extra_deps();



	printf("\n%s: $(deps_%s)\n\n", target, target);

	printf("$(deps_%s):\n", target);

}
@@ -379,13 +360,9 @@ static void parse_dep_file(char *m, const char *target, int insert_extra_deps) 
int main(int argc, char *argv[])

{

	const char *depfile, *target, *cmdline;

	int insert_extra_deps = 0;

	void *buf;



	if (argc == 5 && !strcmp(argv[1], "-e")) {

		insert_extra_deps = 1;

		argv++;

	} else if (argc != 4)

	if (argc != 4)

		usage();



	depfile = argv[1];
@@ -395,7 +372,7 @@ int main(int argc, char *argv[]) 
	printf("cmd_%s := %s\n\n", target, cmdline);



	buf = read_file(depfile);

	parse_dep_file(buf, target, insert_extra_deps);

	parse_dep_file(buf, target);

	free(buf);



	return 0;