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 .<file>.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 <jean-philippe@linaro.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

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