1 files changed, 93 insertions, 0 deletions
diff --git a/src/kernel/arch/amd64/sysenter.s b/src/kernel/arch/amd64/sysenter.s
new file mode 100644
index 0000000..4dfe19d
--- /dev/null
+++ b/src/kernel/arch/amd64/sysenter.s
@@ -0,0 +1,93 @@
+/* TODO include gdt.h */
+.set SEG_r0code, 1
+.set SEG_r3code, 3
+.set SEG_r3data, 4
+
+.set IA32_SYSENTER_CS, 0x174
+.set IA32_SYSENTER_ESP, 0x175
+.set IA32_SYSENTER_EIP, 0x176
+
+.section .text
+.global sysenter_setup
+.type sysenter_setup, @function
+sysenter_setup:
+	xor %rdx, %rdx
+
+	mov $(SEG_r0code << 3), %rax
+	mov $IA32_SYSENTER_CS, %rcx
+	wrmsr
+
+	mov $IA32_SYSENTER_ESP, %rcx
+	mov $0, %rax // unused
+	wrmsr
+
+	mov $IA32_SYSENTER_EIP, %rcx
+	mov $sysenter_stage1, %rax
+	wrmsr
+
+	ret
+
+
+.section .shared
+
+.global stored_eax
+stored_eax:
+.long 0
+
+.global pagedir_current
+// a hack to maintain compat with the old arch api, TODO
+pagedir_current:
+.long 0
+
+.global _sysexit_real
+.type _sysexit_real, @function
+_sysexit_real:
+	xchgw %bx, %bx
+	mov $(SEG_r3data << 3 | 3), %ax
+	mov %ax, %ds
+	mov %ax, %es
+	mov %ax, %fs
+	mov %ax, %gs
+
+	// restore the registers
+	mov $_sysexit_regs, %rsp
+	pop %rdi
+	pop %rsi
+	pop %rbp
+	add $8, %rsp
+	pop %rbx
+	pop %rdx
+	pop %rcx
+	pop %rax
+
+	// enable paging
+	// %rsp used as a scratch register
+	mov (pagedir_current), %rsp
+	mov %rsp, %cr3
+	sysexit
+
+sysenter_stage1:
+	cli /* prevent random IRQs in the middle of kernel code */
+	xchgw %bx, %bx
+
+	//   disable paging
+	// I don't want to damage any of the registers passed in by the user,
+	// so i'm using ESP as a temporary register. At this point there's nothing
+	// useful in it, it's == _bss_end.
+	mov %cr0, %rsp
+	and $0x7FFFFFFF, %rsp  // disable paging
+	mov %rsp, %cr0
+
+	// save the registers
+	mov $(_sysexit_regs + 64), %rsp
+	push %rax
+	push %rcx
+	push %rdx
+	push %rbx
+	push $0x0 // pushal pushes %rsp here, but that's worthless
+	push %rbp
+	push %rsi
+	push %rdi
+
+	mov $_bss_end, %rsp
+	jmp sysenter_stage2