From 2fb81f37d20fd442d1954a7356e3ab7f88314a9c Mon Sep 17 00:00:00 2001
From: Nathan Lee <me@nwlee.tech>
Date: Sat, 13 Jun 2026 21:24:33 -0500
Subject: create support for kernel modules (but don't implement them yet)

---
 Makefile | 121 +++++++++++++++++++++++++++++++++++++++++++++------------------
 1 file changed, 87 insertions(+), 34 deletions(-)

(limited to 'Makefile')

diff --git a/Makefile b/Makefile
index 12aadf8..9465dd1 100644
--- a/Makefile
+++ b/Makefile
@@ -7,7 +7,8 @@ ARCH_FLAG = \
    -march=rv32im \
 	-mabi=ilp32
 
-KERNEL_FLAG = \
+
+COMMON_FLAGS = \
 	-ffreestanding \
 	-fno-builtin \
 	-fno-stack-protector \
@@ -17,68 +18,120 @@ KERNEL_FLAG = \
 	-fno-asynchronous-unwind-tables \
 	-nostdlib \
 	-nostdinc \
-	-static \
-	-nodefaultlibs
+	-nodefaultlibs \
+
+KERNEL_FLAG = $(COMMON_FLAGS) -static
+MODULE_FLAG = $(COMMON_FLAGS) -fPIC -fpie
 
 SECTION_FLAG = \
 	-ffunction-sections \
 	-fdata-sections \
 	-fno-common
 
-INCLUDE_FLAG = -Iinclude -Isrc
+INCLUDE_FLAG = -Iinclude -Ikernel
 OPT_FLAG = -O2 -g3
 WARN_FLAG = -Wall -Wextra -Werror -Wundef
 
-CFLAGS = $(ARCH_FLAG) $(KERNEL_FLAG) $(SECTION_FLAG) $(INCLUDE_FLAG) $(OPT_FLAG) $(WARN_FLAG)
-
-C_SRCS = $(wildcard src/*.c)
-ASM_SRCS = $(wildcard src/*.S)
-
-C_OBJS = $(notdir $(C_SRCS:.c=.o))
-ASM_OBJS = $(notdir $(ASM_SRCS:.S=.o))
-OBJS = $(C_OBJS) $(ASM_OBJS)
-
-KERNEL_ELF = out/bin/wkern.elf
-KERNEL_BIN = out/bin/wkern.bin
-MAP_FILE = out/bin/kernel.map
-
-OBJ_DIR = out/objects
-BIN_DIR = out/bin
-OBJS_PATH = $(addprefix $(OBJ_DIR)/, $(OBJS))
+KERNEL_LD_FLAG = -T linker.ld -fuse-ld=lld -Wl,-nostdlib -Wl,-melf32lriscv -Wl,--gc-sections -Wl,-Map=$(MAP_FILE)
+MODULE_LD_FLAG = -fuse-ld=lld -Wl,-nostdlib -Wl,-shared -Wl,-melf32lriscv -Wl,--gc-sections
 
-LD_FLAG = -T linker.ld -fuse-ld=lld -Wl,-nostdlib -Wl,-melf32lriscv -Wl,--gc-sections -Wl,-Map=$(MAP_FILE)
-OBJCOPY_FLAG = -O binary \
+KERNEL_OBJCOPY_FLAG = -O binary \
 		--strip-all \
 		--remove-section=.comment \
 		--remove-section=.debug* \
 		--remove-section=.note* \
 		--remove-section=.eh_frame \
 		--remove-section=.eh_frame_ptr \
-		--remove-section=.eh_frame_hdr \
+		--remove-section=.eh_frame_hdr
 
+MODULE_OBJCOPY_FLAG = \
+		--strip-debug \
+		--remove-section=.comment \
+		--remove-section=.note*
 
-.PHONY: all clean
-all: $(KERNEL_BIN)
+KERNEL_CFLAGS = $(ARCH_FLAG) $(KERNEL_FLAG) $(SECTION_FLAG) $(INCLUDE_FLAG) $(OPT_FLAG) $(WARN_FLAG)
+MODULE_CFLAGS = $(ARCH_FLAG) $(MODULE_FLAG) $(SECTION_FLAG) $(INCLUDE_FLAG) $(OPT_FLAG) $(WARN_FLAG) -D__KERNEL_MODULE__
 
-$(OBJ_DIR)/%.o: src/%.c | $(OBJ_DIR)
+INCLUDE_DIR = include
+KERNEL_DIR = kernel
+OBJ_DIR = out/objects
+BIN_DIR = out/bin
+MODULE_BIN_DIR = out/modules
+
+MODULES = $(filter-out kernel include out, $(shell find . -maxdepth 1 -type d -printf "%f\n" | grep -v "^\."))
+MODULE_OBJ_DIR = $(addprefix $(OBJ_DIR)/, $(MODULES))
+KERNEL_OBJ_DIR = $(OBJ_DIR)/kernel
+
+KERNEL_C_SRCS = $(wildcard kernel/*.c)
+KERNEL_ASM_SRCS = $(wildcard kernel/*.S)
+KERNEL_C_OBJS = $(addprefix $(OBJ_DIR)/kernel/, $(notdir $(KERNEL_C_SRCS:.c=.o)))
+KERNEL_ASM_OBJS = $(addprefix $(OBJ_DIR)/kernel/, $(notdir $(KERNEL_ASM_SRCS:.S=.o)))
+KERNEL_OBJS = $(KERNEL_C_OBJS) $(KERNEL_ASM_OBJS)
+
+define module_template
+MODULE_$(1)_C_SRCS = $$(wildcard $(1)/*.c)
+MODULE_$(1)_ASM_SRCS = $$(wildcard $(1)/*.S)
+MODULE_$(1)_C_OBJS = $$(addprefix $(OBJ_DIR)/$(1)/, $$(notdir $$(MODULE_$(1)_C_SRCS:.c=.o)))
+MODULE_$(1)_ASM_OBJS = $$(addprefix $(OBJ_DIR)/$(1)/, $$(notdir $$(MODULE_$(1)_ASM_SRCS:.S=.o)))
+MODULE_$(1)_OBJS = $$(MODULE_$(1)_C_OBJS) $$(MODULE_$(1)_ASM_OBJS)
+MODULE_$(1)_KO = $(MODULE_BIN_DIR)/$(1).ko
+endef
+
+$(foreach module,$(MODULES),$(eval $(call module_template,$(module))))
+
+ALL_MODULES = $(foreach module,$(MODULES),$(MODULE_BIN_DIR)/$(module).ko)
+
+KERNEL_ELF = $(BIN_DIR)/wkern.elf
+KERNEL_BIN = $(BIN_DIR)/wkern.bin
+MAP_FILE = $(BIN_DIR)/kernel.map
+ALL_MOODULES = $(foreach module,$(MODULES),$(MODULE_BIN_DIR)/$(module).ko)
+
+MODULE_OBJ_DIRS = $(addprefix $(OBJ_DIR)/, $(MODULES))
+ALL_DIRS = $(OBJ_DIR)/kernel $(MODULE_OBJ_DIRS) $(BIN_DIR) $(MODULE_BIN_DIR)
+
+.PHONY: all clean kernel modules $(MODULES)
+all: kernel modules
+kernel: $(KERNEL_BIN)
+modules: $(ALL_MODULES)
+$(MODULES): %: $(MODULE_BIN_DIR)/%.ko
+
+$(OBJ_DIR)/kernel/%.o: $(KERNEL_DIR)/%.c | $(OBJ_DIR)/kernel
 	@echo " CC $<"
-	$(CC) $(CFLAGS) -c $< -o $@
+	$(CC) $(KERNEL_CFLAGS) -c $< -o $@
 
-$(OBJ_DIR)/%.o: src/%.S | $(OBJ_DIR)
+$(OBJ_DIR)/kernel/%.o: $(KERNEL_DIR)/%.S | $(OBJ_DIR)/kernel
 	@echo " AS $<"
-	$(CC) $(CFLAGS) -c $< -o $@
+	$(CC) $(KERNEL_CFLAGS) -c $< -o $@
 
-$(KERNEL_ELF): $(OBJS_PATH) linker.ld | $(BIN_DIR)
+$(KERNEL_ELF): $(KERNEL_OBJS) linker.ld | $(BIN_DIR)
 	@echo " LD $@"
-	$(CC) $(CFLAGS) $(LD_FLAG) $(OBJS_PATH) -o $@
+	$(CC) $(KERNEL_CFLAGS) $(KERNEL_LD_FLAG) $(KERNEL_OBJS) -o $@
 
 $(KERNEL_BIN): $(KERNEL_ELF) | $(BIN_DIR)
 	@echo " OBJCOPY $@"
 	$(OBJCOPY) $(OBJCOPY_FLAG) $(KERNEL_ELF) $(KERNEL_BIN)
 
-$(OBJ_DIR) $(BIN_DIR):
+$(OBJ_DIR)/%.o: %.c# | $(OBJ_DIR)/%
+	@mkdir -p $(dir $@)
+	@echo " CC $@"
+	$(CC) $(MODULE_CFLAGS) -c $< -o $@
+
+$(OBJ_DIR)/%.o: %.S# | $(OBJ_DIR)/%
+	@mkdir -p $(dir $@)
+	@echo " AS $@"
+	$(CC) $(MODULE_CFLAGS) -c $< -o $@
+
+define module_link_rule
+$(MODULE_BIN_DIR)/$(1).ko: $$(MODULE_$(1)_OBJS) | $(MODULE_BIN_DIR)
+	@echo " LD $$@"
+	$$(CC) $$(MODULE_CFLAGS) $$(MODULE_LD_FLAG) $$^ -o $$@
+	$$(OBJCOPY) $$(MODULE_OBJCOPY_FLAG) $$@ $$@
+endef
+
+$(foreach module,$(MODULES),$(eval $(call module_link_rule,$(module))))
+
+$(ALL_DIRS):
 	mkdir -p $@
 
 clean:
-	rm -rf out 
-
+	rm -rf out
-- 
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