From ed8af51b600fd16d22c6663a241547c3a9d7f2b4 Mon Sep 17 00:00:00 2001 From: Jean-Philippe Brucker Date: Thu, 12 Mar 2020 17:19:45 +0100 Subject: [PATCH] build system: remove KBUILD_STR() When using GNU Make >=4.3, the KBUILD_STR() definition interferes badly with dependency checks during build, and forces a complete rebuild every time Make runs. In if_changed_rule, Kconfig checks if the command used to build a file has changed since last execution. The previous command is stored in the generated ..o.cmd file. For example applets/.applets.o.cmd defines a "cmd_applets/applets.o" variable: cmd_applets/applets.o := gcc ... -D"KBUILD_STR(s)=#s" ... Here the '#' should be escaped with a backslash, otherwise GNU Make interprets it as starting a comment, and ignore the rest of the variable. As a result of this truncation, the previous command doesn't equal the new command and Make rebuilds each target. The problem started to appear when GNU Make 4.3 (released January 2020), introduced a backward-incompatible fix to macros containing a '#'. While the above use of '#', a simple Make variable, still needs to be escaped, a '#' within a function invocation doesn't need to be escaped anymore. As Martin Dorey explained on the GNU Make discussion [1], the above declaration is generated from make-cmd, defined as: make-cmd = $(subst \#,\\\#,$(subst $$,$$$$,$(call escsq,$(cmd_$(1)))) Since GNU Make 4.3, the first argument of subst should not have a backslash. make-cmd now looks for literally \# and doesn't find it, and as a result doesn't add the backslash when generating .o.cmd files. [1] http://savannah.gnu.org/bugs/?20513 We could fix it by changing make-cmd to "$(subst #,\#,...)", but to avoid compatibility headaches, simply get rid of the KBUILD_STR definition, as done in Linux by b42841b7bb62 ("kbuild: Get rid of KBUILD_STR"). Quote the string arguments directly rather than asking the preprocessor to quote them. Signed-off-by: Jean-Philippe Brucker Signed-off-by: Denys Vlasenko --- Makefile.flags | 2 +- scripts/Kbuild.include | 1 + scripts/Makefile.IMA | 1 - scripts/Makefile.lib | 8 ++++---- scripts/trylink | 3 --- 5 files changed, 6 insertions(+), 9 deletions(-) diff --git a/Makefile.flags b/Makefile.flags index e378fbad9..bed766b8a 100644 --- a/Makefile.flags +++ b/Makefile.flags @@ -15,7 +15,7 @@ CPPFLAGS += \ -include include/autoconf.h \ -D_GNU_SOURCE -DNDEBUG \ $(if $(CONFIG_LFS),-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64) \ - -D"BB_VER=KBUILD_STR($(BB_VER))" + -DBB_VER=$(squote)$(quote)$(BB_VER)$(quote)$(squote) CFLAGS += $(call cc-option,-Wall,) CFLAGS += $(call cc-option,-Wshadow,) diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include index 6ec1809a2..5b4db5c2c 100644 --- a/scripts/Kbuild.include +++ b/scripts/Kbuild.include @@ -4,6 +4,7 @@ # Convinient variables comma := , squote := ' +quote := " empty := space := $(empty) $(empty) diff --git a/scripts/Makefile.IMA b/scripts/Makefile.IMA index f155108d7..1e3005864 100644 --- a/scripts/Makefile.IMA +++ b/scripts/Makefile.IMA @@ -49,7 +49,6 @@ OBJCOPY = $(CROSS_COMPILE)objcopy OBJDUMP = $(CROSS_COMPILE)objdump CFLAGS := $(CFLAGS) -CPPFLAGS += -D"KBUILD_STR(s)=\#s" #-Q # We need some generic definitions include $(srctree)/scripts/Kbuild.include diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib index 3e54ea712..d8d768a28 100644 --- a/scripts/Makefile.lib +++ b/scripts/Makefile.lib @@ -81,10 +81,10 @@ obj-dirs := $(addprefix $(obj)/,$(obj-dirs)) # Note: It's possible that one object gets potentially linked into more # than one module. In that case KBUILD_MODNAME will be set to foo_bar, # where foo and bar are the name of the modules. -name-fix = $(subst $(comma),_,$(subst -,_,$1)) -basename_flags = -D"KBUILD_BASENAME=KBUILD_STR($(call name-fix,$(*F)))" +name-fix = $(squote)$(quote)$(subst $(comma),_,$(subst -,_,$1))$(quote)$(squote) +basename_flags = -DKBUILD_BASENAME=$(call name-fix,$(*F)) modname_flags = $(if $(filter 1,$(words $(modname))),\ - -D"KBUILD_MODNAME=KBUILD_STR($(call name-fix,$(modname)))") + -DKBUILD_MODNAME=$(call name-fix,$(modname))) _c_flags = $(CFLAGS) $(EXTRA_CFLAGS) $(CFLAGS_$(*F).o) _a_flags = $(AFLAGS) $(EXTRA_AFLAGS) $(AFLAGS_$(*F).o) @@ -110,7 +110,7 @@ endif c_flags = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(CPPFLAGS) \ $(__c_flags) $(modkern_cflags) \ - -D"KBUILD_STR(s)=\#s" $(basename_flags) $(modname_flags) + $(basename_flags) $(modname_flags) a_flags = -Wp,-MD,$(depfile) $(NOSTDINC_FLAGS) $(CPPFLAGS) \ $(__a_flags) $(modkern_aflags) diff --git a/scripts/trylink b/scripts/trylink index bb6b2de2f..6b74f092d 100755 --- a/scripts/trylink +++ b/scripts/trylink @@ -50,9 +50,6 @@ check_cc() { echo "int main(int argc,char**argv){return argv?argc:0;}" >"$tempname".c # Can use "-o /dev/null", but older gcc tend to *unlink it* on failure! :( # Was using "-xc /dev/null", but we need a valid C program. - # "eval" may be needed if CFLAGS can contain - # '... -D"BB_VER=KBUILD_STR(1.N.M)" ...' - # and we need shell to process quotes! $CC $CFLAGS $LDFLAGS $1 "$tempname".c -o "$tempname" >/dev/null 2>&1 exitcode=$? rm -f "$tempname" "$tempname".c "$tempname".o