Barebones Kernel Commit

Uses limine to boot off of a disk.
Outputs a character to the debug port.

zion/CMakeLists.txt

@@ -0,0 +1,36 @@
+add_executable(zion
+  zion.cpp)
+
+# -c -- Don't run the linker.
+# -nostdlib -- Don't include the standard library.
+# -mabi=sysv -- Explicitly specify the ABI since we will rely on it.
+# -mno-red-zone -- Don't put data below the stack pointer (clobbered by interrupts).
+# -mcmodel=kernel -- Assume the kernel code is running in the higher half.
+# -mgeneral-regs-only -- Prevent GCC from using a whole host of nonsense registers (that we have to enable).
+# Hopefully preceded by -mgeneral-regs-only
+# -mno-80387
+# -mno-mmx
+# -mno-3dnow
+# -mno-sse -mno-sse2
+# -MMD -- Something with the preprocessor?
+set(_Z_COMPILE_FLAGS "${CMAKE_CXX_FLAGS} -ffreestanding -nostdlib -mabi=sysv -mno-red-zone -mcmodel=kernel -mgeneral-regs-only")
+# -mno-80387 -mno-mmx -mno-3dnow -mno-sse -mno-sse2 -MMD
+
+set(_Z_LINK_SCRIPT "${CMAKE_CURRENT_SOURCE_DIR}/linker.ld")
+
+# -lgcc -- Link against gcc internals. Not sure if necessary.
+# -nostdlib -- Don't try to link against the stdlib.
+# -nostartfiles -- Don't try to link against crt0.s
+# -static -- Prevent trying something with shared libraries (probably irrelevant).
+# -z max-page-size=0x1000 -- Assume 4 KiB Pages.
+set(_Z_LINK_FLAGS "-T ${_Z_LINK_SCRIPT} -lgcc -nostdlib -nostartfiles -static -z max-page-size=0x1000")
+
+
+# Don't try to dynamically link.
+set(CMAKE_SHARED_LIBRARY_LINK_CXX_FLAGS "")
+
+set_target_properties(zion
+  PROPERTIES
+  COMPILE_FLAGS "${_Z_COMPILE_FLAGS}"
+  LINK_FLAGS "${_Z_LINK_FLAGS}"
+  )

zion/boot/limine.cfg

@@ -0,0 +1,9 @@
+# Needs to be copied into the EFI partition of the drive.
+
+TIMEOUT=10
+
+:AcadiaOS
+
+PROTOCOL=limine
+
+KERNEL_PATH=boot:///zion

zion/linker.ld

@@ -0,0 +1,44 @@
+OUTPUT_FORMAT(elf64-x86-64)
+
+ENTRY (zion)
+
+/* Define the program headers we want so the bootloader gives us the right */
+/* MMU permissions */
+PHDRS
+{
+    text    PT_LOAD    FLAGS((1 << 0) | (1 << 2)) ; /* Execute + Read */
+    rodata  PT_LOAD    FLAGS((1 << 2)) ;            /* Read only */
+    data    PT_LOAD    FLAGS((1 << 1) | (1 << 2)) ; /* Write + Read */
+}
+
+SECTIONS
+{
+  . = 0xffffffff80000000;
+	/* Add a symbol that indicates the start address of the kernel. */
+	_kernel_start = .;
+
+	.text : {
+			*(.text .text.*)
+	} :text
+
+	/* Move to the next memory page for .rodata */
+	. += CONSTANT(MAXPAGESIZE);
+
+	.rodata : {
+			*(.rodata .rodata.*)
+	} :rodata
+
+	/* Move to the next memory page for .data */
+	. += CONSTANT(MAXPAGESIZE);
+
+	.data : {
+			*(.data .data.*)
+	} :data
+
+	.bss : {
+			*(COMMON)
+			*(.bss .bss.*)
+	} :data
+	/* Add a symbol that indicates the end address of the kernel. */
+	_kernel_end = .;
+}

zion/zion.cpp

@@ -0,0 +1,14 @@
+#include <stdint.h>
+
+#define COM1 0x3f8
+
+void outb(uint16_t port, uint8_t value) {
+  asm volatile("outb %0, %1" ::"a"(value), "Nd"(port));
+}
+
+extern "C" void zion() {
+  outb(COM1, 'a');
+
+  while (1)
+    ;
+}