From 4b86e6272166236c9283004f6a060d5174165796 Mon Sep 17 00:00:00 2001
From: Bad Diode <bd@badd10de.dev>
Date: Tue, 7 Sep 2021 10:48:33 +0200
Subject: Initial commit: bootstrap

---
 Makefile      | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 src/linker.ld | 34 ++++++++++++++++++++++++++++++++++
 src/main.c    |  3 +++
 src/start.s   | 11 +++++++++++
 4 files changed, 95 insertions(+)
 create mode 100644 Makefile
 create mode 100644 src/linker.ld
 create mode 100644 src/main.c
 create mode 100644 src/start.s

diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..475c160
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,47 @@
+.POSIX:
+.SUFFIXES:
+.PHONY: clean run
+
+# Compiler.
+AS      := arm-none-eabi-as
+CC      := arm-none-eabi-gcc
+OBJCOPY := arm-none-eabi-objcopy
+
+# Paths.
+SRC_DIR   := src
+BUILD_DIR := build
+
+# Output files.
+ELF := $(BUILD_DIR)/kernel7.elf
+IMG := $(BUILD_DIR)/kernel7.img
+
+# Bootstrapping files.
+OBJ_START = $(BUILD_DIR)/start.o
+OBJ_MAIN = $(BUILD_DIR)/main.o
+SRC_LINK = $(SRC_DIR)/linker.ld
+
+CFLAGS := -Wall -ffreestanding -O2 -nostdlib -lgcc -mgeneral-regs-only
+AFLAGS :=
+
+default: $(IMG)
+
+$(BUILD_DIR)/%.o: $(SRC_DIR)/%.s
+	$(AS) $(AFLAGS) -o $@ -c $<
+
+$(BUILD_DIR)/%.o: $(SRC_DIR)/%.c
+	$(CC) $(CFLAGS) -o $@ -c $<
+
+$(IMG): $(BUILD_DIR) $(ELF)
+	$(OBJCOPY) $(ELF) -O binary $(IMG)
+
+$(ELF): $(OBJ_START) $(OBJ_MAIN)
+	$(CC) $(CFLAGS) -T $(SRC_LINK) -o $(ELF) $(OBJ_START) $(OBJ_MAIN)
+
+clean:
+	rm -rf $(BUILD_DIR)
+
+$(BUILD_DIR):
+	mkdir -p $(BUILD_DIR)
+
+run: $(IMG)
+	qemu-system-aarch64 -M raspi3 -kernel $(IMG) -d in_asm -serial null -serial stdio
diff --git a/src/linker.ld b/src/linker.ld
new file mode 100644
index 0000000..f3482e9
--- /dev/null
+++ b/src/linker.ld
@@ -0,0 +1,34 @@
+ENTRY(_start)
+
+SECTIONS
+{
+    . = 0x8000;
+    __start = .;
+    .text :
+    {
+        KEEP(*(.text.boot))
+        *(.text)
+    }
+    . = ALIGN(4096);
+    .rodata :
+    {
+        *(.rodata)
+    }
+    . = ALIGN(4096);
+    .data :
+    {
+        *(.data)
+    }
+    . = ALIGN(4096);
+    __bss_start = .;
+    .bss :
+    {
+        bss = .;
+        *(.bss)
+    }
+    . = ALIGN(4096);
+    __bss_end = .;
+    __bss_size = __bss_end - __bss_start;
+    __end = .;
+}
+
diff --git a/src/main.c b/src/main.c
new file mode 100644
index 0000000..1ce2dd1
--- /dev/null
+++ b/src/main.c
@@ -0,0 +1,3 @@
+void main(void) {
+    while(1);
+}
diff --git a/src/start.s b/src/start.s
new file mode 100644
index 0000000..0fd2a5f
--- /dev/null
+++ b/src/start.s
@@ -0,0 +1,11 @@
+.section ".text.boot"
+
+.global _start
+
+_start:
+    ldr r3, =main
+    blx r3
+
+halt:
+    wfe
+    b halt
-- 
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