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Date: Mon, 19 Nov 2018 22:47:00 -0500 (EST)
From: Nicolas Pitre <nicolas.pitre@...aro.org>
To: Masahiro Yamada <yamada.masahiro@...ionext.com>
cc: linux-kbuild@...r.kernel.org, Sam Ravnborg <sam@...nborg.org>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
linux-arch@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
Michael Ellerman <mpe@...erman.id.au>,
linux-kernel@...r.kernel.org,
Michal Marek <michal.lkml@...kovi.net>,
Will Deacon <will.deacon@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 5/9] kbuild: simplify dependency generation for
CONFIG_TRIM_UNUSED_KSYMS
On Tue, 20 Nov 2018, Masahiro Yamada wrote:
> 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@...ionext.com>
Nice work.
Reviewed-by: Nicolas Pitre <nico@...aro.org>
> ---
>
> Changes in v2:
> - Let gen_ksymdeps.sh add dependencies to .*.cmd file directly
> - Fix typos
>
> include/asm-generic/export.h | 13 ++++++++-----
> include/linux/export.h | 18 +++++++++---------
> scripts/Kbuild.include | 28 ----------------------------
> scripts/Makefile.build | 7 +++++++
> scripts/basic/fixdep.c | 31 ++++---------------------------
> scripts/gen_ksymdeps.sh | 25 +++++++++++++++++++++++++
> 6 files changed, 53 insertions(+), 69 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..fd8711e 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_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)
> diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
> index 6cf6a8b..4b943f4 100644
> --- a/scripts/Kbuild.include
> +++ b/scripts/Kbuild.include
> @@ -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).
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 4f94579..c23ee45 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -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
> 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
>
>
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