From 01a8bd6af7db5b51ab82adfa235da968eb2d8e97 Mon Sep 17 00:00:00 2001
From: Alejandro Colomar <alx@kernel.org>
Date: Sat, 20 May 2023 21:00:49 +0200
Subject: Makefile: Create a preprocessed file, and allow appending flags

Signed-off-by: Alejandro Colomar <alx@kernel.org>
---
 Makefile | 43 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 32 insertions(+), 11 deletions(-)

diff --git a/Makefile b/Makefile
index eacfd63..ff498ce 100644
--- a/Makefile
+++ b/Makefile
@@ -11,18 +11,34 @@ builddir := tmp
 LIBUNIT_PREFIX := /opt/local/unit
 
 
-LIBUNIT_CFLAGS := -isystem$(LIBUNIT_PREFIX)/include
-LIBUNIT_LIBS   := -L$(LIBUNIT_PREFIX)/lib -lunit
+LIBUNIT_CPPFLAGS := -isystem$(LIBUNIT_PREFIX)/include
+LIBUNIT_LIBS     := -L$(LIBUNIT_PREFIX)/lib -lunit
 
-CFLAGS  := -Wall -Wextra -Werror -std=gnu2x -O3 $(LIBUNIT_CFLAGS)
-ASFLAGS :=
-LDFLAGS :=
-LIBS    := $(LIBUNIT_LIBS) -lpthread -lc -lgcc
+DEFAULT_CPPFLAGS := $(LIBUNIT_CPPFLAGS)
+EXTRA_CPPFLAGS   :=
+CPPFLAGS         := $(DEFAULT_CPPFLAGS) $(EXTRA_CPPFLAGS)
 
-AR := ar
-AS := as
-CC := cc
-LD := $(CC) $(CFLAGS)
+DEFAULT_CFLAGS   := -Wall -Wextra -Werror -std=gnu2x -O3
+EXTRA_CFLAGS     :=
+CFLAGS           := $(DEFAULT_CFLAGS) $(EXTRA_CFLAGS)
+
+DEFAULT_ASFLAGS  :=
+EXTRA_ASFLAGS    :=
+ASFLAGS          := $(DEFAULT_ASFLAGS) $(EXTRA_ASFLAGS)
+
+DEFAULT_LDFLAGS  :=
+EXTRA_LDFLAGS    :=
+LDFLAGS          := $(DEFAULT_LDFLAGS) $(EXTRA_LDFLAGS)
+
+DEFAULT_LIBS     := $(LIBUNIT_LIBS) -lpthread -lc -lgcc
+EXTRA_LIBS       :=
+LIBS             := $(DEFAULT_LIBS) $(EXTRA_LIBS)
+
+AR  := ar
+AS  := as
+CC  := cc
+CPP := $(CC) -E $(CFLAGS)
+LD  := $(CC) $(CFLAGS)
 
 
 FIND  := find
@@ -34,6 +50,7 @@ SORT  := sort
 
 SRCDIR := $(srcdir)/src
 SRC    := $(shell $(FIND) $(SRCDIR) -type f | $(GREP) '\.c$$' | $(SORT))
+I      := $(patsubst $(srcdir)/%.c,$(builddir)/%.i,$(SRC))
 ASM    := $(patsubst $(srcdir)/%.c,$(builddir)/%.s,$(SRC))
 OBJ    := $(patsubst %.s,%.o,$(ASM))
 BIN    := $(builddir)/unit_c_app
@@ -49,7 +66,11 @@ all: $(BIN)
 .SECONDEXPANSION:
 
 
-$(ASM): $(builddir)/%.s: $(srcdir)/%.c Makefile | $$(@D)/
+$(I): $(builddir)/%.i: $(srcdir)/%.c Makefile | $$(@D)/
+	$(info	CPP	$@)
+	$(CPP) $(CPPFLAGS) -o $@ $<
+
+$(ASM): %.s: %.i Makefile | $$(@D)/
 	$(info CC	$@)
 	$(CC) -S $(CFLAGS) -o $@ $<
 
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