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kbuild: simplify dependency generation for CONFIG_TRIM_UNUSED_KSYMS

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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: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Nicolas Pitre <nico@linaro.org>
This commit is contained in:
Masahiro Yamada 2018-11-30 10:05:26 +09:00
parent ee3e46b7ef
commit bbda5ec671
6 changed files with 55 additions and 71 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
include/asm-generic/export.h
View File

@ -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)

22
include/linux/export.h
View File

@ -92,22 +92,22 @@ struct kernel_symbol {
*/
#define __EXPORT_SYMBOL(sym, sec)
#elif defined(__KSYM_DEPS__)
/*
* 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).
*/
#define __EXPORT_SYMBOL(sym, sec) === __KSYM_##sym ===
#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 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 __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)

28
scripts/Kbuild.include
View File

@ -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).

7
scripts/Makefile.build
View File

@ -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

31
scripts/basic/fixdep.c
View File

@ -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;

25
scripts/gen_ksymdeps.sh Executable file
View File

@ -0,0 +1,25 @@
#!/bin/sh
# SPDX-License-Identifier: GPL-2.0
set -e
# List of exported symbols
ksyms=$($NM $1 | sed -n 's/.*__ksym_marker_\(.*\)/\1/p' | tr A-Z a-z)
if [ -z "$ksyms" ]; then
exit 0
fi
echo
echo "ksymdeps_$1 := \\"
for s in $ksyms
do
echo $s | sed -e 's:^_*: $(wildcard include/ksym/:' \
-e 's:__*:/:g' -e 's/$/.h) \\/'
done
echo
echo "$1: \$(ksymdeps_$1)"
echo
echo "\$(ksymdeps_$1):"