From ed8af51b600fd16d22c6663a241547c3a9d7f2b4 Mon Sep 17 00:00:00 2001 From: Jean-Philippe Brucker Date: Thu, 12 Mar 2020 17:19:45 +0100 Subject: 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 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'Makefile.flags') 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,) -- cgit v1.2.3