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kbuild: simplify dependency generation for CONFIG_TRIM_UNUSED_KSYMS

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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@socionext.com>
Reviewed-by: Nicolas Pitre <nico@linaro.org>
This commit is contained in:
Masahiro Yamada
2018-11-30 10:05:26 +09:00
parent ee3e46b7ef
commit bbda5ec671
6 changed files with 55 additions and 71 deletions
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28
scripts/Kbuild.include
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@@ -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).