scheduler: yield

src/arch/x86_64/Makefile

@@ -1,4 +1,4 @@
-objects := $(patsubst %.c,%.o,$(wildcard *.c)) israsm.o context.o syscall.o
+objects := $(patsubst %.c,%.o,$(wildcard *.c)) israsm.o context.o syscall.o sched.o
 subdirs=boot
 OBJPATH=$(OBJDIR)/arch/${TARGET}/
 export
@@ -23,3 +23,7 @@ syscall.o: syscall.asm
 	nasm -f elf64 -o $@ $<
 	mkdir -p $(OBJPATH)
 	cp $@ $(OBJPATH)/$@
+sched.o: sched.asm
+	nasm -f elf64 -o $@ $<
+	mkdir -p $(OBJPATH)
+	cp $@ $(OBJPATH)/$@

src/arch/x86_64/sched.asm

@@ -0,0 +1,66 @@
+section .text
+
+global arch_sched_yieldtrampoline
+
+; C sysv abi
+; rdi -> thread ptr
+; rsi -> regs ptr
+
+REGSTRUCTSIZE equ 208
+
+arch_sched_yieldtrampoline:
+
+	; save return address to save as rip later
+	pop r10
+
+	; save rsp to reuse later
+	mov r11, rsp
+	
+	; temporarily change rsp to set values for the regs structure
+
+	mov rsp, rsi
+	add rsp, REGSTRUCTSIZE
+
+	; build the structure
+
+	
+	mov r9, ss
+	push r9
+	push r11 ; saved rsp
+	pushfq
+	mov r9, cs
+	push r9
+	push r10 ; rip
+	push qword 0 ; err
+	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 r9,ds
+	push r9
+	mov r9,es
+	push r9
+	push qword 0 ; fs
+	push qword 0 ; gs
+	mov r10, cr2
+	push r10
+
+	; restore old stack pointer
+
+	mov rsp, r11
+	
+	extern sched_yieldtrampoline
+	call sched_yieldtrampoline
+
+	; the switch call never returns