mirror of
https://github.com/torvalds/linux.git
synced 2024-12-27 13:22:23 +00:00
5e9e95cc91
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 negative opinions about this slowness in commits: -5cf0fd591f("Kbuild: disable TRIM_UNUSED_KSYMS option") -a555bdd0c5("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 used by modules. Commitf73edc8951("kbuild: unify two modpost invocations") is another ground-work to do this in a one-pass algorithm. With the list of modules, modpost sets sym->used if it is used by a module. modpost emits KSYMTAB only for symbols with sym->used==true. BTW, Nicolas explained why the trimming was implemented with recursion: https://lore.kernel.org/all/2o2rpn97-79nq-p7s2-nq5-8p83391473r@syhkavp.arg/ 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 I guess that is unlikely to happen. Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
155 lines
4.7 KiB
Makefile
155 lines
4.7 KiB
Makefile
# SPDX-License-Identifier: GPL-2.0
|
|
# ===========================================================================
|
|
# Module versions
|
|
# ===========================================================================
|
|
#
|
|
# Stage one of module building created the following:
|
|
# a) The individual .o files used for the module
|
|
# b) A <module>.o file which is the .o files above linked together
|
|
# c) A <module>.mod file, listing the name of the preliminary <module>.o file,
|
|
# plus all .o files
|
|
# d) modules.order, which lists all the modules
|
|
|
|
# Stage 2 is handled by this file and does the following
|
|
# 1) Find all modules listed in modules.order
|
|
# 2) modpost is then used to
|
|
# 3) create one <module>.mod.c file per module
|
|
# 4) create one Module.symvers file with CRC for all exported symbols
|
|
|
|
# Step 3 is used to place certain information in the module's ELF
|
|
# section, including information such as:
|
|
# Version magic (see include/linux/vermagic.h for full details)
|
|
# - Kernel release
|
|
# - SMP is CONFIG_SMP
|
|
# - PREEMPT is CONFIG_PREEMPT[_RT]
|
|
# - GCC Version
|
|
# Module info
|
|
# - Module version (MODULE_VERSION)
|
|
# - Module alias'es (MODULE_ALIAS)
|
|
# - Module license (MODULE_LICENSE)
|
|
# - See include/linux/module.h for more details
|
|
|
|
# Step 4 is solely used to allow module versioning in external modules,
|
|
# where the CRC of each module is retrieved from the Module.symvers file.
|
|
|
|
PHONY := __modpost
|
|
__modpost:
|
|
|
|
include include/config/auto.conf
|
|
include $(srctree)/scripts/Kbuild.include
|
|
|
|
MODPOST = scripts/mod/modpost
|
|
|
|
modpost-args = \
|
|
$(if $(CONFIG_MODVERSIONS),-m) \
|
|
$(if $(CONFIG_MODULE_SRCVERSION_ALL),-a) \
|
|
$(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E) \
|
|
$(if $(KBUILD_MODPOST_WARN),-w) \
|
|
$(if $(KBUILD_NSDEPS),-d $(MODULES_NSDEPS)) \
|
|
$(if $(CONFIG_MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS)$(KBUILD_NSDEPS),-N) \
|
|
$(if $(findstring 1, $(KBUILD_EXTRA_WARN)),-W) \
|
|
-o $@
|
|
|
|
modpost-deps := $(MODPOST)
|
|
|
|
# 'make -i -k' ignores compile errors, and builds as many modules as possible.
|
|
ifneq ($(findstring i,$(filter-out --%,$(MAKEFLAGS))),)
|
|
modpost-args += -n
|
|
endif
|
|
|
|
# Read out modules.order to pass in modpost.
|
|
# Otherwise, allmodconfig would fail with "Argument list too long".
|
|
ifdef KBUILD_MODULES
|
|
modpost-args += -T $(MODORDER)
|
|
modpost-deps += $(MODORDER)
|
|
endif
|
|
|
|
ifeq ($(KBUILD_EXTMOD),)
|
|
|
|
# Generate the list of in-tree objects in vmlinux
|
|
# ---------------------------------------------------------------------------
|
|
|
|
# This is used to retrieve symbol versions generated by genksyms.
|
|
ifdef CONFIG_MODVERSIONS
|
|
vmlinux.symvers Module.symvers: .vmlinux.objs
|
|
endif
|
|
|
|
# Ignore libgcc.a
|
|
# Some architectures do '$(CC) --print-libgcc-file-name' to borrow libgcc.a
|
|
# from the toolchain, but there is no EXPORT_SYMBOL in it.
|
|
|
|
quiet_cmd_vmlinux_objs = GEN $@
|
|
cmd_vmlinux_objs = \
|
|
for f in $(real-prereqs); do \
|
|
case $${f} in \
|
|
*libgcc.a) ;; \
|
|
*) $(AR) t $${f} ;; \
|
|
esac \
|
|
done > $@
|
|
|
|
targets += .vmlinux.objs
|
|
.vmlinux.objs: vmlinux.a $(KBUILD_VMLINUX_LIBS) FORCE
|
|
$(call if_changed,vmlinux_objs)
|
|
|
|
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 -u , $(ksym-wl))
|
|
modpost-deps += $(ksym-wl)
|
|
endif
|
|
|
|
ifeq ($(wildcard vmlinux.o),)
|
|
missing-input := vmlinux.o
|
|
output-symdump := modules-only.symvers
|
|
else
|
|
modpost-args += vmlinux.o
|
|
modpost-deps += vmlinux.o
|
|
output-symdump := $(if $(KBUILD_MODULES), Module.symvers, vmlinux.symvers)
|
|
endif
|
|
|
|
else
|
|
|
|
# set src + obj - they may be used in the modules's Makefile
|
|
obj := $(KBUILD_EXTMOD)
|
|
src := $(obj)
|
|
|
|
# Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
|
|
include $(kbuild-file)
|
|
|
|
output-symdump := $(KBUILD_EXTMOD)/Module.symvers
|
|
|
|
ifeq ($(wildcard Module.symvers),)
|
|
missing-input := Module.symvers
|
|
else
|
|
modpost-args += -i Module.symvers
|
|
modpost-deps += Module.symvers
|
|
endif
|
|
|
|
modpost-args += -e $(addprefix -i , $(KBUILD_EXTRA_SYMBOLS))
|
|
|
|
endif # ($(KBUILD_EXTMOD),)
|
|
|
|
quiet_cmd_modpost = MODPOST $@
|
|
cmd_modpost = \
|
|
$(if $(missing-input), \
|
|
echo >&2 "WARNING: $(missing-input) is missing."; \
|
|
echo >&2 " Modules may not have dependencies or modversions."; \
|
|
echo >&2 " You may get many unresolved symbol errors."; \
|
|
echo >&2 " You can set KBUILD_MODPOST_WARN=1 to turn errors into warning"; \
|
|
echo >&2 " if you want to proceed at your own risk.";) \
|
|
$(MODPOST) $(modpost-args)
|
|
|
|
targets += $(output-symdump)
|
|
$(output-symdump): $(modpost-deps) FORCE
|
|
$(call if_changed,modpost)
|
|
|
|
__modpost: $(output-symdump)
|
|
PHONY += FORCE
|
|
FORCE:
|
|
|
|
existing-targets := $(wildcard $(sort $(targets)))
|
|
|
|
-include $(foreach f,$(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
|
|
|
|
.PHONY: $(PHONY)
|