kernel: syscalls

kernel-src/arch/x86-64/syscall.asm

@@ -0,0 +1,109 @@
+section .rodata
+syscalltab:
+
+syscallcount equ 0
+section .text
+global arch_syscall_entry
+; on entry:
+; rcx has the return address
+; r11 has the old rflags
+; syscall arguments:
+; rax has the syscall number
+; rdi has the first argument
+; rsi has the second argument
+; rdx has the third argument
+; r10 has the fourth argument
+; r8 has the fifth argument
+; r9 has the sixth argument
+; return:
+; rdx has errno
+; rax has return value
+arch_syscall_entry:
+	swapgs
+	; save return address on user stack
+	push rcx
+	mov rcx, [gs:0x0] ; thread pointer
+	mov rcx, [rcx] ; kernel stack top
+	xchg rsp, rcx ; switch stack pointers
+
+	; push context
+	push qword 0x1b ; user SS
+	push qword rcx
+	add qword [rsp], 8 ; correct the old stack pointer to before the return address push
+	push r11     ; rflags is stored in r11
+	push qword 0x23 ; user CS
+	push qword [rcx] ; save return RIP
+	push qword 0 ; error
+	push rbp
+	push rsi
+	push rdi
+	push r15
+	push r14
+	push r13
+	push r12
+	push r11
+	push r10
+	push r9
+	push r8
+	push rdx
+	push rcx
+	push rbx
+	push rax
+	mov rbx, ds
+	push rbx
+	mov rbx, es
+	push rbx
+	mov rbx, fs
+	push rbx
+	mov rbx, gs
+	push rbx
+	mov rbx, cr2
+	push rbx
+
+	; prepare arguments for the functions
+	push r9
+	mov r9, r8
+	mov r8, r10
+	mov rcx, rdx
+	mov rdx, rsi
+	mov rsi, rdi
+	mov rdi, rsp
+	sti
+
+	cmp rax, syscallcount
+	jae .nosyscall
+	call [syscalltab + rax * 8]
+	jmp .return
+	.nosyscall:
+	extern syscall_invalid
+	call syscall_invalid
+	.return:
+	cli
+	; restore context
+	add rsp, 32 ; r9 argument, cr2, gs, and fs are not popped.
+	pop rbx
+	mov es,rbx
+	pop rbx
+	mov ds,rbx
+	add rsp, 8 ; rax
+	pop rbx
+	pop rcx
+	add rsp, 8 ; rdx
+	pop r8
+	pop r9
+	pop r10
+	pop r11
+	pop r12
+	pop r13
+	pop r14
+	pop r15
+	pop rdi
+	pop rsi
+	pop rbp
+	add rsp, 8 ; remove error code
+	pop rcx
+	add rsp, 8 ; user CS
+	pop r11    ; rflags
+	pop rsp
+	swapgs
+	o64 sysret