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 <yamada.masahiro@socionext.com>
Reviewed-by: Nicolas Pitre <nico@linaro.org>

1 files changed, 0 insertions, 28 deletions

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 6cf6a8b83b97..4b943f4d2226 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).