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masahir0ymasahir0y
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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: Masahiro Yamada <[email protected]> Reviewed-by: Nicolas Pitre <[email protected]>
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6 files changed

Lines changed: 53 additions & 69 deletions

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‎include/asm-generic/export.h‎

Lines changed: 8 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -59,16 +59,19 @@ __kcrctab_\name:
5959
.endm
6060
#undef __put
6161

62-
#if defined(__KSYM_DEPS__)
63-
64-
#define __EXPORT_SYMBOL(sym, val, sec) === __KSYM_##sym ===
65-
66-
#elif defined(CONFIG_TRIM_UNUSED_KSYMS)
62+
#if defined(CONFIG_TRIM_UNUSED_KSYMS)
6763

6864
#include <linux/kconfig.h>
6965
#include <generated/autoksyms.h>
7066

67+
.macro __ksym_marker sym
68+
.section ".discard.ksym","a"
69+
__ksym_marker_\sym:
70+
.previous
71+
.endm
72+
7173
#define __EXPORT_SYMBOL(sym, val, sec) \
74+
__ksym_marker sym; \
7275
__cond_export_sym(sym, val, sec, __is_defined(__KSYM_##sym))
7376
#define __cond_export_sym(sym, val, sec, conf) \
7477
___cond_export_sym(sym, val, sec, conf)

‎include/linux/export.h‎

Lines changed: 9 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -92,22 +92,22 @@ struct kernel_symbol {
9292
*/
9393
#define __EXPORT_SYMBOL(sym, sec)
9494

95-
#elif defined(__KSYM_DEPS__)
95+
#elif defined(CONFIG_TRIM_UNUSED_KSYMS)
96+
97+
#include <generated/autoksyms.h>
9698

9799
/*
98100
* For fine grained build dependencies, we want to tell the build system
99101
* about each possible exported symbol even if they're not actually exported.
100-
* We use a string pattern that is unlikely to be valid code that the build
101-
* system filters out from the preprocessor output (see ksym_dep_filter
102-
* in scripts/Kbuild.include).
102+
* We use a symbol pattern __ksym_marker_<symbol> that the build system filters
103+
* from the $(NM) output (see scripts/gen_ksymdeps.sh). These symbols are
104+
* discarded in the final link stage.
103105
*/
104-
#define __EXPORT_SYMBOL(sym, sec) === __KSYM_##sym ===
105-
106-
#elif defined(CONFIG_TRIM_UNUSED_KSYMS)
107-
108-
#include <generated/autoksyms.h>
106+
#define __ksym_marker(sym) \
107+
static int __ksym_marker_##sym[0] __section(".discard.ksym") __used
109108

110109
#define __EXPORT_SYMBOL(sym, sec) \
110+
__ksym_marker(sym); \
111111
__cond_export_sym(sym, sec, __is_defined(__KSYM_##sym))
112112
#define __cond_export_sym(sym, sec, conf) \
113113
___cond_export_sym(sym, sec, conf)

‎scripts/Kbuild.include‎

Lines changed: 0 additions & 28 deletions
Original file line numberDiff line numberDiff line change
@@ -260,39 +260,11 @@ if_changed_dep = $(if $(strip $(any-prereq) $(arg-check) ), \
260260
@set -e; \
261261
$(cmd_and_fixdep), @:)
262262

263-
ifndef CONFIG_TRIM_UNUSED_KSYMS
264-
265263
cmd_and_fixdep = \
266264
$(echo-cmd) $(cmd_$(1)); \
267265
scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).cmd;\
268266
rm -f $(depfile);
269267

270-
else
271-
272-
# Filter out exported kernel symbol names from the preprocessor output.
273-
# See also __KSYM_DEPS__ in include/linux/export.h.
274-
# We disable the depfile generation here, so as not to overwrite the existing
275-
# depfile while fixdep is parsing it.
276-
flags_nodeps = $(filter-out -Wp$(comma)-M%, $($(1)))
277-
ksym_dep_filter = \
278-
case "$(1)" in \
279-
cc_*_c|cpp_i_c) \
280-
$(CPP) $(call flags_nodeps,c_flags) -D__KSYM_DEPS__ $< ;; \
281-
as_*_S|cpp_s_S) \
282-
$(CPP) $(call flags_nodeps,a_flags) -D__KSYM_DEPS__ $< ;; \
283-
boot*|build*|cpp_its_S|*cpp_lds_S|dtc|host*|vdso*) : ;; \
284-
*) echo "Don't know how to preprocess $(1)" >&2; false ;; \
285-
esac | tr ";" "\n" | sed -n 's/^.*=== __KSYM_\(.*\) ===.*$$/_\1/p'
286-
287-
cmd_and_fixdep = \
288-
$(echo-cmd) $(cmd_$(1)); \
289-
$(ksym_dep_filter) | \
290-
scripts/basic/fixdep -e $(depfile) $@ '$(make-cmd)' \
291-
> $(dot-target).cmd; \
292-
rm -f $(depfile);
293-
294-
endif
295-
296268
# Usage: $(call if_changed_rule,foo)
297269
# Will check if $(cmd_foo) or any of the prerequisites changed,
298270
# and if so will execute $(rule_foo).

‎scripts/Makefile.build‎

Lines changed: 7 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -254,9 +254,15 @@ objtool_dep = $(objtool_obj) \
254254
$(wildcard include/config/orc/unwinder.h \
255255
include/config/stack/validation.h)
256256

257+
ifdef CONFIG_TRIM_UNUSED_KSYMS
258+
cmd_gen_ksymdeps = \
259+
$(CONFIG_SHELL) $(srctree)/scripts/gen_ksymdeps.sh $@ >> $(dot-target).cmd;
260+
endif
261+
257262
define rule_cc_o_c
258263
$(call echo-cmd,checksrc) $(cmd_checksrc) \
259264
$(call cmd_and_fixdep,cc_o_c) \
265+
$(cmd_gen_ksymdeps) \
260266
$(cmd_checkdoc) \
261267
$(call echo-cmd,objtool) $(cmd_objtool) \
262268
$(cmd_modversions_c) \
@@ -265,6 +271,7 @@ endef
265271

266272
define rule_as_o_S
267273
$(call cmd_and_fixdep,as_o_S) \
274+
$(cmd_gen_ksymdeps) \
268275
$(call echo-cmd,objtool) $(cmd_objtool) \
269276
$(cmd_modversions_S)
270277
endef

‎scripts/basic/fixdep.c‎

Lines changed: 4 additions & 27 deletions
Original file line numberDiff line numberDiff line change
@@ -105,8 +105,7 @@
105105

106106
static void usage(void)
107107
{
108-
fprintf(stderr, "Usage: fixdep [-e] <depfile> <target> <cmdline>\n");
109-
fprintf(stderr, " -e insert extra dependencies given on stdin\n");
108+
fprintf(stderr, "Usage: fixdep <depfile> <target> <cmdline>\n");
110109
exit(1);
111110
}
112111

@@ -131,21 +130,6 @@ static void print_dep(const char *m, int slen, const char *dir)
131130
printf(".h) \\\n");
132131
}
133132

134-
static void do_extra_deps(void)
135-
{
136-
char buf[80];
137-
138-
while (fgets(buf, sizeof(buf), stdin)) {
139-
int len = strlen(buf);
140-
141-
if (len < 2 || buf[len - 1] != '\n') {
142-
fprintf(stderr, "fixdep: bad data on stdin\n");
143-
exit(1);
144-
}
145-
print_dep(buf, len - 1, "include/ksym");
146-
}
147-
}
148-
149133
struct item {
150134
struct item *next;
151135
unsigned int len;
@@ -293,7 +277,7 @@ static int is_ignored_file(const char *s, int len)
293277
* assignments are parsed not only by make, but also by the rather simple
294278
* parser in scripts/mod/sumversion.c.
295279
*/
296-
static void parse_dep_file(char *m, const char *target, int insert_extra_deps)
280+
static void parse_dep_file(char *m, const char *target)
297281
{
298282
char *p;
299283
int is_last, is_target;
@@ -369,23 +353,16 @@ static void parse_dep_file(char *m, const char *target, int insert_extra_deps)
369353
exit(1);
370354
}
371355

372-
if (insert_extra_deps)
373-
do_extra_deps();
374-
375356
printf("\n%s: $(deps_%s)\n\n", target, target);
376357
printf("$(deps_%s):\n", target);
377358
}
378359

379360
int main(int argc, char *argv[])
380361
{
381362
const char *depfile, *target, *cmdline;
382-
int insert_extra_deps = 0;
383363
void *buf;
384364

385-
if (argc == 5 && !strcmp(argv[1], "-e")) {
386-
insert_extra_deps = 1;
387-
argv++;
388-
} else if (argc != 4)
365+
if (argc != 4)
389366
usage();
390367

391368
depfile = argv[1];
@@ -395,7 +372,7 @@ int main(int argc, char *argv[])
395372
printf("cmd_%s := %s\n\n", target, cmdline);
396373

397374
buf = read_file(depfile);
398-
parse_dep_file(buf, target, insert_extra_deps);
375+
parse_dep_file(buf, target);
399376
free(buf);
400377

401378
return 0;

‎scripts/gen_ksymdeps.sh‎

Lines changed: 25 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,25 @@
1+
#!/bin/sh
2+
# SPDX-License-Identifier: GPL-2.0
3+
4+
set -e
5+
6+
# List of exported symbols
7+
ksyms=$($NM $1 | sed -n 's/.*__ksym_marker_\(.*\)/\1/p' | tr A-Z a-z)
8+
9+
if [ -z "$ksyms" ]; then
10+
exit 0
11+
fi
12+
13+
echo
14+
echo "ksymdeps_$1 := \\"
15+
16+
for s in $ksyms
17+
do
18+
echo $s | sed -e 's:^_*: $(wildcard include/ksym/:' \
19+
-e 's:__*:/:g' -e 's/$/.h) \\/'
20+
done
21+
22+
echo
23+
echo "$1: \$(ksymdeps_$1)"
24+
echo
25+
echo "\$(ksymdeps_$1):"

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