From d79436a1170e4d5ffde77416313587f320c8e590 Mon Sep 17 00:00:00 2001
From: Miquel Sabaté Solà <mikisabate@gmail.com>
Date: Mon, 18 Nov 2024 15:56:37 +0100
Subject: usr: Bootstrap the initramfs for the kernel
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Introduce a sample `foo` program which already calls the
`write_and_block` system call which is yet to be implemented by this
kernel. Moreover, the same CPIO format is used for the initramfs as with
Linux, so we can pass it with QEMU without worries.

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>
---
 Makefile | 49 +++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 39 insertions(+), 10 deletions(-)

(limited to 'Makefile')

diff --git a/Makefile b/Makefile
index df82342..6799281 100644
--- a/Makefile
+++ b/Makefile
@@ -18,15 +18,19 @@ endif
 # no `-mcpu`, no `-mtune`, no funny business.
 
 CC    = $(CROSS_COMPILE)gcc$(CC_SUFFIX)
+AS    = $(CROSS_COMPILE)as$(CC_SUFFIX)
 LD    = $(CROSS_COMPILE)ld
 QEMU ?= qemu-system-riscv64
 
 ISA     ?= rv64imafdc_zicntr_zicsr_zifencei_zihpm_zca_zcd_zba_zbb
-CCFLAGS  = -march=$(ISA) -Iinclude/ -mabi=lp64d
+ASFLAGS  = -march=$(ISA) -mabi=lp64d
+CCFLAGS  = $(ASFLAGS) -Iinclude/
 CCFLAGS += -Werror -Wpedantic -Wall -Wextra -Wcast-align -Wcast-qual -Winit-self \
            -Wmissing-include-dirs -Wredundant-decls -Wshadow -Wsign-conversion \
-           -Wswitch-default -Wundef -Wunreachable-code -Wmissing-noreturn
-LDFLAGS  = -Iinclude/ -static -nostdlib -melf64lriscv -z noexecstack
+           -Wswitch-default -Wundef -Wunreachable-code -Wmissing-noreturn \
+           -nostdinc -nostdlib -std=gnu17
+LDFLAGS  = -Iinclude/ -static -melf64lriscv -z noexecstack
+USRFLAGS = -static -melf64lriscv
 
 ##
 # Optional parameters for QEMU and gdb.
@@ -42,26 +46,29 @@ GDB_EXTRA_FLAGS ?=
 DEBUG =
 ifeq ($(strip $(DEBUG)),)
 	CCFLAGS += -O3
+	QEMU_FLAGS += -nographic
 else
 	CCFLAGS += -g
 	QEMU_FLAGS += -s -S
 endif
 
 ##
-# Paths.
+# Paths
 
 SRC    = $(wildcard kernel/head.S kernel/*.c)
 OBJ    = $(patsubst %.c,%.o,$(patsubst %.S,%.o,$(SRC)))
 LINKER = kernel/fbos.ld
 KRNL   = fbos
+USR    = usr/bin/foo
+INIT   = usr/initramfs.cpio
 
 LDFLAGS += -T $(LINKER)
 
 ##
-# Targets
+# Kernel
 
 .PHONY: all
-all: clean $(KRNL)
+all: clean $(KRNL) usr
 
 .PHONY: $(KRNL)
 $(KRNL): $(OBJ) $(LINKER).S
@@ -78,12 +85,34 @@ $(KRNL): $(OBJ) $(LINKER).S
 	$(E) "	CC	" $(*F)
 	$(Q) $(CC) $(CCFLAGS) -c $< -o $@
 
+##
+# User space
+
+.PHONY: usr
+usr: $(USR)
+	$(E) "	CPIO	" $(INIT)
+	$(Q) find usr/bin/ -type f -executable | cpio -o --quiet -H newc > $(INIT)
+
+usr/src/%.o: usr/src/%.S
+	$(E) "	AS	" $(basename $@)
+	$(Q) $(AS) $(ASFLAGS) -c $< -o $@
+
+usr/bin/%: usr/src/%.o
+	$(E) "	LD	" $@
+	$(Q) $(LD) $(USRFLAGS) $< -o $@
+
+# HACK: do not remove object files from usr/src/.
+.SECONDARY:
+
+##
+# Hacking
+
 .PHONY: qemu
-qemu: $(KRNL)
+qemu: $(KRNL) usr
 ifeq ($(strip $(QEMU_BIOS)),)
-	$(Q) $(QEMU) $(QEMU_FLAGS) -machine virt -kernel $(KRNL) -nographic
+	$(Q) $(QEMU) $(QEMU_FLAGS) -machine virt -kernel $(KRNL) -initrd $(INIT)
 else
-	$(Q) $(QEMU) $(QEMU_FLAGS) -machine virt -bios $(QEMU_BIOS) -kernel $(KRNL) -nographic
+	$(Q) $(QEMU) $(QEMU_FLAGS) -machine virt -bios $(QEMU_BIOS) -kernel $(KRNL) -initrd $(INIT)
 endif
 
 .PHONY: gdb
@@ -92,7 +121,7 @@ gdb:
 
 .PHONY: clean
 clean:
-	$(Q) rm -f $(OBJ) $(KRNL) $(LINKER)
+	$(Q) rm -f $(OBJ) $(KRNL) $(LINKER) $(USR) usr/src/*.o $(INIT)
 
 .PHONY: lint
 lint:
-- 
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