[PATCH 4/8] kbuild: simplify dependency generation for CONFIG_TRIM_UNUSED_KSYMS

From: Masahiro Yamada
Date: Thu Nov 15 2018 - 03:29:00 EST

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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@xxxxxxxxxxxxx>
---

include/asm-generic/export.h | 13 ++++++++-----
include/linux/export.h | 18 +++++++++---------
scripts/Kbuild.include | 29 -----------------------------
scripts/Makefile.build | 10 ++++++++++
scripts/basic/fixdep.c | 31 ++++---------------------------
scripts/gen_ksymdeps.sh | 25 +++++++++++++++++++++++++
6 files changed, 56 insertions(+), 70 deletions(-)
create mode 100755 scripts/gen_ksymdeps.sh

diff --git a/include/asm-generic/export.h b/include/asm-generic/export.h
index 4d73e6e..294d6ae 100644
--- a/include/asm-generic/export.h
+++ b/include/asm-generic/export.h
@@ -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)
diff --git a/include/linux/export.h b/include/linux/export.h
index ce764a5..0413a3d 100644
--- a/include/linux/export.h
+++ b/include/linux/export.h
@@ -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_ksymdep.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)
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index bb01555..1eafc85 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -260,41 +260,12 @@ 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).tmp;\
rm -f $(depfile); \
mv -f $(dot-target).tmp $(dot-target).cmd;

-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).tmp; \
- rm -f $(depfile); \
- mv -f $(dot-target).tmp $(dot-target).cmd;
-
-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).
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 7f3ca6e..e5ba9b1 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -254,9 +254,18 @@ 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).tmp; \
+ cat $(dot-target).tmp >> $(dot-target).cmd; \
+ rm -f $(dot-target).tmp;
+
+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 +274,7 @@ 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
diff --git a/scripts/basic/fixdep.c b/scripts/basic/fixdep.c
index 850966f3..facbd60 100644
--- a/scripts/basic/fixdep.c
+++ b/scripts/basic/fixdep.c
@@ -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;
diff --git a/scripts/gen_ksymdeps.sh b/scripts/gen_ksymdeps.sh
new file mode 100755
index 0000000..1324986
--- /dev/null
+++ b/scripts/gen_ksymdeps.sh
@@ -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):"
--
2.7.4

Next message: Masahiro Yamada: "[PATCH 1/8] kbuild: remove redundant 'set -e' from filechk_* defines"
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