3 files changed, 87 insertions, 0 deletions
diff --git a/src/platform/asm.h b/src/platform/asm.h
new file mode 100644
index 0000000..6f72617
--- /dev/null
+++ b/src/platform/asm.h
@@ -0,0 +1,9 @@
+#pragma once
+
+// boot.s
+__attribute__((noreturn))
+void halt_cpu();
+
+// sysenter.c
+void sysexit(void (*fun)(), void *stack_top);
+void sysenter_setup();
diff --git a/src/platform/boot.s b/src/platform/boot.s
new file mode 100644
index 0000000..d5bfda5
--- /dev/null
+++ b/src/platform/boot.s
@@ -0,0 +1,47 @@
+.set MAGIC, 0x1BADB002
+.set FLAG_ALIGN,   1<<0 /* align modules on page boundaries */
+.set FLAG_MEMINFO, 1<<1 /* memory map */
+.set FLAGS,        FLAG_ALIGN | FLAG_MEMINFO
+.set CHECKSUM, -(MAGIC + FLAGS)
+
+.section .multiboot
+.align 4
+.long MAGIC
+.long FLAGS
+.long CHECKSUM
+
+/* a lil stack */
+.section .bss
+.global stack_top
+.type stack_top, @object
+.align 16
+stack_bottom:
+.skip 16384
+stack_top:
+
+
+.section .text
+.global _start
+.type _start, @function
+_start:
+	mov $stack_top, %esp
+	call kmain
+
+.global halt_cpu
+.type halt_cpu, @function
+halt_cpu:
+	cli
+1:	hlt
+	jmp 1b
+
+// temporary, will be moved to another file soon
+.global change_cs
+.type change_cs, @function
+change_cs:
+	/* retf pops off the return address and code segment off the stack.
+	 * it turns out that in the i386 cdecl calling convention they're in
+	 * the correct place already.
+	 */
+	retf
+
+.size _start, . - _start
diff --git a/src/platform/sysenter.s b/src/platform/sysenter.s
new file mode 100644
index 0000000..270dc08
--- /dev/null
+++ b/src/platform/sysenter.s
@@ -0,0 +1,31 @@
+/* kernel/gdt.c */
+.set SEG_r0code, 1
+.set SEG_r3code, 3
+.set SEG_r3data, 4
+
+.set IA32_SYSENTER_CS, 0x174
+
+.section .text
+.global sysexit
+.type sysexit, @function
+sysexit:
+	pop %ecx
+	pop %edx
+
+	mov $(SEG_r3data << 3 | 3), %ax
+	mov %ax, %ds
+	mov %ax, %es
+	mov %ax, %fs
+	mov %ax, %gs
+
+	sysexit
+
+
+.global sysenter_setup
+.type sysenter_setup, @function
+sysenter_setup:
+	xor %edx, %edx
+	mov $(SEG_r0code << 3), %eax
+	mov $IA32_SYSENTER_CS, %ecx
+	wrmsr
+	ret