When CONFIG_TRIM_UNUSED_KSYMS is enabled, Kbuild recursively traverses
the directory tree to determine which EXPORT_SYMBOL to trim. If an
EXPORT_SYMBOL turns out to be unused by anyone, Kbuild begins the
second traverse, where some source files are recompiled with their
EXPORT_SYMBOL() tuned into a no-op.
Linus stated a negative opinion about this slowness in commits:
- 5cf0fd591f2e ("Kbuild: disable TRIM_UNUSED_KSYMS option")
- a555bdd0c58c ("Kbuild: enable TRIM_UNUSED_KSYMS again, with some guarding")
We can do this better now. The final data structures of EXPORT_SYMBOL
are generated by the modpost stage, so modpost can selectively emit
KSYMTAB entries that are really referenced by modules.
modpost needs to know all defined symbols in all modules (that is,
EXPORT_SYMBOL's that have users). Commit 8da79d44fd2e ("kbuild:
unify two modpost invocations") is a ground-work to do this in
one-pass.
Nicolas explained why the trimming was implemented with recursion:
https://lore.kernel.org/all/2o2rpn97-79nq-p7s2-nq5-8p83391473r@xxxxxxxxxxx/
Actually, we never achieved that level of optimization where the chain
reaction of trimming comes into play because:
- CONFIG_LTO_CLANG cannot remove any unused symbols
- CONFIG_LD_DEAD_CODE_DATA_ELIMINATION is enabled only for vmlinux,
but not modules
If deeper trimming is required, we need to revisit this, but that is
unlikely to happen.
Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
---
Changes in v2:
- New patch
.gitignore | 1 -
Makefile | 24 ++++--------
include/linux/export.h | 41 ---------------------
scripts/Makefile.build | 7 ----
scripts/Makefile.modpost | 8 +++-
scripts/adjust_autoksyms.sh | 73 -------------------------------------
scripts/basic/fixdep.c | 3 +-
scripts/gen_autoksyms.sh | 62 -------------------------------
scripts/gen_ksymdeps.sh | 30 ---------------
scripts/link-vmlinux.sh | 5 ++-
scripts/mod/modpost.c | 54 ++++++++++++++++++++++++---
scripts/remove-stale-files | 2 +
12 files changed, 70 insertions(+), 240 deletions(-)
delete mode 100755 scripts/adjust_autoksyms.sh
delete mode 100755 scripts/gen_autoksyms.sh
delete mode 100755 scripts/gen_ksymdeps.sh
diff --git a/.gitignore b/.gitignore
index 265959544978..a9b44cd36066 100644
--- a/.gitignore
+++ b/.gitignore
@@ -103,7 +103,6 @@ modules.order
#
/include/config/
/include/generated/
-/include/ksym/
/arch/*/include/generated/
# stgit generated dirs
diff --git a/Makefile b/Makefile
index 2b4980490ecb..36ae888c37b3 100644
--- a/Makefile
+++ b/Makefile
@@ -1120,28 +1120,13 @@ endif
export KBUILD_VMLINUX_LIBS
export KBUILD_LDS := arch/$(SRCARCH)/kernel/vmlinux.lds
-# Recurse until adjust_autoksyms.sh is satisfied
-PHONY += autoksyms_recursive
ifdef CONFIG_TRIM_UNUSED_KSYMS
# For the kernel to actually contain only the needed exported symbols,
# we have to build modules as well to determine what those symbols are.
# (this can be evaluated only once include/config/auto.conf has been included)
KBUILD_MODULES := 1
-
-autoksyms_recursive: $(build-dir) modules.order
- $(Q)$(CONFIG_SHELL) $(srctree)/scripts/adjust_autoksyms.sh \
- "$(MAKE) -f $(srctree)/Makefile autoksyms_recursive"
endif
-autoksyms_h := $(if $(CONFIG_TRIM_UNUSED_KSYMS), include/generated/autoksyms.h)
-
-quiet_cmd_autoksyms_h = GEN $@
- cmd_autoksyms_h = mkdir -p $(dir $@); \
- $(CONFIG_SHELL) $(srctree)/scripts/gen_autoksyms.sh $@
-
-$(autoksyms_h):
- $(call cmd,autoksyms_h)
-
# '$(AR) mPi' needs 'T' to workaround the bug of llvm-ar <= 14
quiet_cmd_ar_vmlinux.a = AR $@
cmd_ar_vmlinux.a = \
@@ -1153,7 +1138,7 @@ targets += vmlinux.a
vmlinux.a: $(KBUILD_VMLINUX_OBJS) scripts/head-object-list.txt FORCE
$(call if_changed,ar_vmlinux.a)
-vmlinux.o: autoksyms_recursive vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
+vmlinux.o: vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.vmlinux_o
ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)
@@ -1168,6 +1153,11 @@ vmlinux: scripts/link-vmlinux.sh vmlinux.o $(KBUILD_LDS) modpost FORCE
targets += vmlinux
+# When .vmlinux.export.c is updated, vmlinux must be relinked.
+# (REVISIT for refactoring)
+.vmlinux.export.c: modpost
+ @:
+
# The actual objects are generated when descending,
# make sure no implicit rule kicks in
$(sort $(KBUILD_LDS) $(KBUILD_VMLINUX_OBJS) $(KBUILD_VMLINUX_LIBS)): . ;
@@ -1195,7 +1185,7 @@ scripts: scripts_basic scripts_dtc
PHONY += prepare archprepare
archprepare: outputmakefile archheaders archscripts scripts include/config/kernel.release \
- asm-generic $(version_h) $(autoksyms_h) include/generated/utsrelease.h \
+ asm-generic $(version_h) include/generated/utsrelease.h \
include/generated/compile.h include/generated/autoconf.h remove-stale-files
prepare0: archprepare
diff --git a/include/linux/export.h b/include/linux/export.h
index 0c71577cf8bb..d9fb1ebb535c 100644
--- a/include/linux/export.h
+++ b/include/linux/export.h
@@ -63,47 +63,6 @@ extern struct module __this_module;
*/
#define __EXPORT_SYMBOL(sym, sec, ns)
-#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.
- */
-
-#ifdef __ASSEMBLY__
-
-#define __ksym_marker(sym) \
- .section ".discard.ksym","a" ; \
-__ksym_marker_##sym: ; \
- .previous
-
-#else
-
-#define __ksym_marker(sym) \
- static int __ksym_marker_##sym[0] __section(".discard.ksym") __used
-
-#endif
-
-#define __EXPORT_SYMBOL(sym, sec, ns) \
- __ksym_marker(sym); \
- __cond_export_sym(sym, sec, ns, __is_defined(__KSYM_##sym))
-#define __cond_export_sym(sym, sec, ns, conf) \
- ___cond_export_sym(sym, sec, ns, conf)
-#define ___cond_export_sym(sym, sec, ns, enabled) \
- __cond_export_sym_##enabled(sym, sec, ns)
-#define __cond_export_sym_1(sym, sec, ns) ___EXPORT_SYMBOL(sym, sec, ns)
-
-#ifdef __GENKSYMS__
-#define __cond_export_sym_0(sym, sec, ns) __GENKSYMS_EXPORT_SYMBOL(sym)
-#else
-#define __cond_export_sym_0(sym, sec, ns) /* nothing */
-#endif
-
#else
#define __EXPORT_SYMBOL(sym, sec, ns) ___EXPORT_SYMBOL(sym, sec, ns)
diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 4c1d0bd1bc03..64f652b03d29 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -218,16 +218,10 @@ is-standard-object = $(if $(filter-out y%, $(OBJECT_FILES_NON_STANDARD_$(basetar
$(obj)/%.o: objtool-enabled = $(if $(is-standard-object),$(if $(delay-objtool),$(is-single-obj-m),y))
-ifdef CONFIG_TRIM_UNUSED_KSYMS
-cmd_gen_ksymdeps = \
- $(CONFIG_SHELL) $(srctree)/scripts/gen_ksymdeps.sh $@ >> $(dot-target).cmd
-endif
-
cmd_check_local_export = $(srctree)/scripts/check-local-export $@
define rule_cc_o_c
$(call cmd_and_fixdep,cc_o_c)
- $(call cmd,gen_ksymdeps)
$(call cmd,check_local_export)
$(call cmd,checksrc)
$(call cmd,checkdoc)
@@ -238,7 +232,6 @@ endef
define rule_as_o_S
$(call cmd_and_fixdep,as_o_S)
- $(call cmd,gen_ksymdeps)
$(call cmd,check_local_export)
$(call cmd,gen_objtooldep)
$(call cmd,gen_symversions_S)
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index 7740ce3b29e8..555b9e741a01 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -86,6 +86,12 @@ output-symdump := $(if $(vmlinux.o-if-present), Module.symvers, modules-only.sym
missing-input := $(filter-out $(vmlinux.o-if-present),vmlinux.o)
endif
+ifdef CONFIG_TRIM_UNUSED_KSYMS
+ksym-wl := $(CONFIG_UNUSED_KSYMS_WHITELIST)
+ksym-wl := $(if $(filter-out /%, $(ksym-wl)),$(srctree)/)$(ksym-wl)
+modpost-args += -t $(addprefix -W, $(ksym-wl))
+endif
+
else
# set src + obj - they may be used in the modules's Makefile
@@ -122,7 +128,7 @@ quiet_cmd_modpost = MODPOST $@
sed 's/ko$$/o/' $(or $(modorder-if-needed), /dev/null) | $(MODPOST) $(modpost-args) $(vmlinux.o-if-present) -T -
targets += $(output-symdump)
-$(output-symdump): $(modorder-if-needed) $(vmlinux.o-if-present) $(moudle.symvers-if-present) $(MODPOST) FORCE
+$(output-symdump): $(modorder-if-needed) $(vmlinux.o-if-present) $(moudle.symvers-if-present) $(MODPOST) $(ksym-wl) FORCE
$(call if_changed,modpost)
__modpost: $(output-symdump)
diff --git a/scripts/adjust_autoksyms.sh b/scripts/adjust_autoksyms.sh
deleted file mode 100755
index f1b5ac818411..000000000000
--- a/scripts/adjust_autoksyms.sh
+++ /dev/null
@@ -1,73 +0,0 @@
-#!/bin/sh
-# SPDX-License-Identifier: GPL-2.0-only
-
-# Script to update include/generated/autoksyms.h and dependency files
-#
-# Copyright: (C) 2016 Linaro Limited
-# Created by: Nicolas Pitre, January 2016
-#
-
-# Update the include/generated/autoksyms.h file.
-#
-# For each symbol being added or removed, the corresponding dependency
-# file's timestamp is updated to force a rebuild of the affected source
-# file. All arguments passed to this script are assumed to be a command
-# to be exec'd to trigger a rebuild of those files.
-
-set -e
-
-cur_ksyms_file="include/generated/autoksyms.h"
-new_ksyms_file="include/generated/autoksyms.h.tmpnew"
-
-info() {
- if [ "$quiet" != "silent_" ]; then
- printf " %-7s %s\n" "$1" "$2"
- fi
-}
-
-info "CHK" "$cur_ksyms_file"
-
-# Use "make V=1" to debug this script.
-case "$KBUILD_VERBOSE" in
-*1*)
- set -x
- ;;
-esac
-
-# Generate a new symbol list file
-$CONFIG_SHELL $srctree/scripts/gen_autoksyms.sh --modorder "$new_ksyms_file"
-
-# Extract changes between old and new list and touch corresponding
-# dependency files.
-changed=$(
-count=0
-sort "$cur_ksyms_file" "$new_ksyms_file" | uniq -u |
-sed -n 's/^#define __KSYM_\(.*\) 1/\1/p' |
-while read sympath; do
- if [ -z "$sympath" ]; then continue; fi
- depfile="include/ksym/${sympath}"
- mkdir -p "$(dirname "$depfile")"
- touch "$depfile"
- # Filesystems with coarse time precision may create timestamps
- # equal to the one from a file that was very recently built and that
- # needs to be rebuild. Let's guard against that by making sure our
- # dep files are always newer than the first file we created here.
- while [ ! "$depfile" -nt "$new_ksyms_file" ]; do
- touch "$depfile"
- done
- echo $((count += 1))
-done | tail -1 )
-changed=${changed:-0}
-
-if [ $changed -gt 0 ]; then
- # Replace the old list with tne new one
- old=$(grep -c "^#define __KSYM_" "$cur_ksyms_file" || true)
- new=$(grep -c "^#define __KSYM_" "$new_ksyms_file" || true)
- info "KSYMS" "symbols: before=$old, after=$new, changed=$changed"
- info "UPD" "$cur_ksyms_file"
- mv -f "$new_ksyms_file" "$cur_ksyms_file"
- # Then trigger a rebuild of affected source files
- exec $@
-else
- rm -f "$new_ksyms_file"
-fi
diff --git a/scripts/basic/fixdep.c b/scripts/basic/fixdep.c
index 2328f9a641da..e7db12140d87 100644
--- a/scripts/basic/fixdep.c
+++ b/scripts/basic/fixdep.c
@@ -243,8 +243,7 @@ static void *read_file(const char *filename)
/* Ignore certain dependencies */
static int is_ignored_file(const char *s, int len)
{
- return str_ends_with(s, len, "include/generated/autoconf.h") ||
- str_ends_with(s, len, "include/generated/autoksyms.h");
+ return str_ends_with(s, len, "include/generated/autoconf.h");
}
/*
diff --git a/scripts/gen_autoksyms.sh b/scripts/gen_autoksyms.sh
deleted file mode 100755
index 653fadbad302..000000000000
--- a/scripts/gen_autoksyms.sh
+++ /dev/null
@@ -1,62 +0,0 @@
-#!/bin/sh
-# SPDX-License-Identifier: GPL-2.0-only
-
-# Create an autoksyms.h header file from the list of all module's needed symbols
-# as recorded in *.usyms files and the user-provided symbol whitelist.
-
-set -e
-
-# Use "make V=1" to debug this script.
-case "$KBUILD_VERBOSE" in
-*1*)
- set -x
- ;;
-esac
-
-read_modorder=
-
-if [ "$1" = --modorder ]; then
- shift
- read_modorder=1
-fi
-
-output_file="$1"
-
-needed_symbols=
-
-# Special case for modversions (see modpost.c)
-if grep -q "^CONFIG_MODVERSIONS=y$" include/config/auto.conf; then
- needed_symbols="$needed_symbols module_layout"
-fi
-
-ksym_wl=$(sed -n 's/^CONFIG_UNUSED_KSYMS_WHITELIST=\(.*\)$/\1/p' include/config/auto.conf)
-if [ -n "$ksym_wl" ]; then
- [ "${ksym_wl}" != "${ksym_wl#/}" ] || ksym_wl="$abs_srctree/$ksym_wl"
- if [ ! -f "$ksym_wl" ] || [ ! -r "$ksym_wl" ]; then
- echo "ERROR: '$ksym_wl' whitelist file not found" >&2
- exit 1
- fi
-fi
-
-# Generate a new ksym list file with symbols needed by the current
-# set of modules.
-cat > "$output_file" << EOT
-/*
- * Automatically generated file; DO NOT EDIT.
- */
-
-EOT
-
-{
- [ -n "${read_modorder}" ] && sed 's/ko$/usyms/' modules.order | xargs cat
- echo "$needed_symbols"
- [ -n "$ksym_wl" ] && cat "$ksym_wl"
-} | sed -e 's/ /\n/g' | sed -n -e '/^$/!p' |
-# Remove the dot prefix for ppc64; symbol names with a dot (.) hold entry
-# point addresses.
-sed -e 's/^\.//' |
-sort -u |
-# Ignore __this_module. It's not an exported symbol, and will be resolved
-# when the final .ko's are linked.
-grep -v '^__this_module$' |
-sed -e 's/\(.*\)/#define __KSYM_\1 1/' >> "$output_file"
diff --git a/scripts/gen_ksymdeps.sh b/scripts/gen_ksymdeps.sh
deleted file mode 100755
index 8ee533f33659..000000000000
--- a/scripts/gen_ksymdeps.sh
+++ /dev/null
@@ -1,30 +0,0 @@
-#!/bin/sh
-# SPDX-License-Identifier: GPL-2.0
-
-set -e
-
-# List of exported symbols
-#
-# If the object has no symbol, $NM warns 'no symbols'.
-# Suppress the stderr.
-# TODO:
-# Use -q instead of 2>/dev/null when we upgrade the minimum version of
-# binutils to 2.37, llvm to 13.0.0.
-ksyms=$($NM $1 2>/dev/null | sed -n 's/.*__ksym_marker_\(.*\)/\1/p')
-
-if [ -z "$ksyms" ]; then
- exit 0
-fi
-
-echo
-echo "ksymdeps_$1 := \\"
-
-for s in $ksyms
-do
- printf ' $(wildcard include/ksym/%s) \\\n' "$s"
-done
-
-echo
-echo "$1: \$(ksymdeps_$1)"
-echo
-echo "\$(ksymdeps_$1):"
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 2782c5d1518b..9c3140d33ccd 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -305,4 +305,7 @@ if is_enabled CONFIG_KALLSYMS; then
fi
# For fixdep
-echo "vmlinux: $0" > .vmlinux.d
+echo "vmlinux: $0 \\" > .vmlinux.d
+if is_enabled CONFIG_MODULES; then
+ echo .vmlinux.export.c >> .vmlinux.d
+fi
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 90733664a602..1e9eba0a6cec 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -34,6 +34,9 @@ static bool warn_unresolved;
static int sec_mismatch_count;
static bool sec_mismatch_warn_only = true;
+/* Trim EXPORT_SYMBOLs that are unused by in-tree modules */
+static bool trim_unused_exports;
+
/* ignore missing files */
static bool ignore_missing_files;
/* If set to 1, only warn (instead of error) about missing ns imports */
@@ -216,6 +219,7 @@ struct symbol {
bool weak;
bool is_func;
bool is_gpl_only; /* exported by EXPORT_SYMBOL_GPL */
+ bool used; /* there exists a user of this symbol */
char name[];
};
@@ -1872,6 +1876,7 @@ static void check_exports(struct module *mod)
continue;
}
+ exp->used = true;
s->module = exp->module;
s->crc_valid = exp->crc_valid;
s->crc = exp->crc;
@@ -1895,6 +1900,23 @@ static void check_exports(struct module *mod)
}
}
+static void handle_white_list_exports(const char *white_list)
+{
+ char *buf, *p, *name;
+
+ buf = read_text_file(white_list);
+ p = buf;
+
+ while ((name = strsep(&p, "\n"))) {
+ struct symbol *sym = find_symbol(name);
+
+ if (sym)
+ sym->used = true;
+ }
+
+ free(buf);
+}
+
static void check_modname_len(struct module *mod)
{
const char *mod_name;
@@ -1965,10 +1987,14 @@ static void add_exported_symbols(struct buffer *buf, struct module *mod)
/* generate struct for exported symbols */
buf_printf(buf, "\n");
- list_for_each_entry(sym, &mod->exported_symbols, list)
+ list_for_each_entry(sym, &mod->exported_symbols, list) {
+ if (trim_unused_exports && !sym->used)
+ continue;
+
buf_printf(buf, "KSYMTAB_%s(%s, \"%s\", \"%s\");\n",
sym->is_func ? "FUNC" : "DATA", sym->name,
sym->is_gpl_only ? "_gpl" : "", sym->namespace);
+ }
if (!modversions)
return;
@@ -1976,6 +2002,9 @@ static void add_exported_symbols(struct buffer *buf, struct module *mod)
/* record CRCs for exported symbols */
buf_printf(buf, "\n");
list_for_each_entry(sym, &mod->exported_symbols, list) {
+ if (trim_unused_exports && !sym->used)
+ continue;
+
if (!sym->crc_valid)
warn("EXPORT symbol \"%s\" [%s%s] version generation failed, symbol will not be versioned.\n"
"Is \"%s\" prototyped in <asm/asm-prototypes.h>?\n",
@@ -2139,9 +2168,6 @@ static void write_mod_c_file(struct module *mod)
char fname[PATH_MAX];
int ret;
- check_modname_len(mod);
- check_exports(mod);
-
add_header(&buf, mod);
add_exported_symbols(&buf, mod);
add_versions(&buf, mod);
@@ -2275,12 +2301,13 @@ int main(int argc, char **argv)
{
struct module *mod;
char *missing_namespace_deps = NULL;
+ char *unused_exports_white_list = NULL;
char *dump_write = NULL, *files_source = NULL;
int opt;
LIST_HEAD(dump_lists);
struct dump_list *dl, *dl2;
- while ((opt = getopt(argc, argv, "ei:mnT:o:awENd:")) != -1) {
+ while ((opt = getopt(argc, argv, "ei:mntT:tW:o:awENd:")) != -1) {
switch (opt) {
case 'e':
external_module = true;
@@ -2305,6 +2332,12 @@ int main(int argc, char **argv)
case 'T':
files_source = optarg;
break;
+ case 't':
+ trim_unused_exports = true;
+ break;
+ case 'W':
+ unused_exports_white_list = optarg;
+ break;
case 'w':
warn_unresolved = true;
break;
@@ -2334,6 +2367,17 @@ int main(int argc, char **argv)
if (files_source)
read_symbols_from_files(files_source);
+ list_for_each_entry(mod, &modules, list) {
+ if (mod->from_dump || mod->is_vmlinux)
+ continue;
+
+ check_modname_len(mod);
+ check_exports(mod);
+ }
+
+ if (unused_exports_white_list)
+ handle_white_list_exports(unused_exports_white_list);
+
list_for_each_entry(mod, &modules, list) {
if (mod->from_dump)
continue;
diff --git a/scripts/remove-stale-files b/scripts/remove-stale-files
index ccadfa3afb2b..d2009eda270a 100755
--- a/scripts/remove-stale-files
+++ b/scripts/remove-stale-files
@@ -47,3 +47,5 @@ rm -f arch/riscv/purgatory/kexec-purgatory.c
rm -f scripts/extract-cert
rm -f arch/x86/purgatory/kexec-purgatory.c
+
+rm -rf include/ksym
--
2.34.1
