system calls

src/arch/x86_64/Makefile

@@ -1,4 +1,4 @@
-objects := $(patsubst %.c,%.o,$(wildcard *.c)) israsm.o context.o
+objects := $(patsubst %.c,%.o,$(wildcard *.c)) israsm.o context.o syscall.o
 subdirs=boot
 OBJPATH=$(OBJDIR)/arch/${TARGET}/
 export
@@ -19,3 +19,7 @@ context.o: context.asm
 	nasm -f elf64 -o $@ $<
 	mkdir -p $(OBJPATH)
 	cp $@ $(OBJPATH)/$@
+syscall.o: syscall.asm
+	nasm -f elf64 -o $@ $<
+	mkdir -p $(OBJPATH)
+	cp $@ $(OBJPATH)/$@

src/arch/x86_64/context.asm

@@ -1,15 +1,21 @@
 global arch_switchcontext
 arch_switchcontext:
 	mov rsp,rdi
-	add rsp, 8 ; cr2
+	add rsp, 24 ; cr2 gs fs
-        pop rax
+
-        mov gs,rax
+	mov rbx,es
-        pop rax
+	pop rax
-        mov fs,rax
+	cmp rax,rbx
-        pop rax
+	jne .segswap
+	add rsp,8 ; ds
+	jmp .genreg
+	.segswap:
+	swapgs
         mov es,rax
-        pop rax
+	pop rax
         mov ds,rax
+	
+	.genreg:
         pop rax
         pop rbx
         pop rcx
@@ -27,6 +33,4 @@ arch_switchcontext:
         pop rbp
         add rsp,8 ; remove error code
 	
-	swapgs
-	
 	iretq

src/arch/x86_64/cpu.c

@@ -8,6 +8,8 @@
 // syscall, sse, etc
 // for the current cpu
 
+extern void asm_syscall_entry();
+
 void cpu_state_init(){
 	
 	// syscall
@@ -28,7 +30,7 @@ void cpu_state_init(){
 		star |= (uint64_t)0x28 << 32;
 		
 		wrmsr(MSR_STAR, star);
-		wrmsr(MSR_LSTAR, 0xDEADBEEF); // FIXME add 64 bit handler here
+		wrmsr(MSR_LSTAR, asm_syscall_entry);
 		wrmsr(MSR_CSTAR, 0); // no compat mode syscall handler
 		wrmsr(MSR_FMASK, 0x200); // disable interrupts on syscall
 	}

src/arch/x86_64/gdt.c

@@ -34,8 +34,10 @@ static void reloadgdtr(){
 	
 gdtr.offset = &arch_getcls()->gdt;
 gdtr.size   = sizeof(gdt_t) - 1;
-	asm("lgdt (%%rax)" : : "a"(&gdtr) : "memory");
+	asm volatile("lgdt (%%rax)" : : "a"(&gdtr) : "memory");
-	asm("ltr %%ax" : : "a"(0x48));
+	asm volatile("ltr %%ax" : : "a"(0x48));
+	asm volatile("swapgs;mov $0, %%ax;mov %%ax, %%gs;mov %%ax, %%fs;swapgs;" : : : "ax");
+
 }
 
 void gdt_init(){

src/arch/x86_64/include/arch/cls.h

@@ -13,6 +13,7 @@
 // this will be pointed to by GS and will contain per cpu info
 
 typedef struct{
+	void* kstack;
 	gdt_t gdt;
 	ist_t ist;
 	int lapicid;

src/arch/x86_64/include/arch/regs.h

@@ -4,10 +4,15 @@
 #include <stdint.h>
 #include <stdbool.h>
 
+typedef struct{
+	uint64_t gsbase, fsbase;
+} arch_extraregs;
+
 typedef struct{
         uint64_t cr2,gs,fs,es,ds,rax,rbx,rcx,rdx,r8,r9,r10,r11,r12,r13,r14,r15,rdi,rsi,rbp,error,rip,cs,rflags,rsp,ss;
 } arch_regs;
-
+void arch_regs_saveextra(arch_extraregs* regs);
+void arch_regs_setupextra(arch_extraregs* regs);
 void arch_regs_setupkernel(arch_regs* regs, void* ip, void* stack, bool interrupts);
 void arch_regs_setupuser(arch_regs* regs, void* ip, void* stack, bool interrupts);
 

src/arch/x86_64/isr.asm

@@ -29,7 +29,7 @@ section .text
 	mov rax, gs
 	push rax
 
-	cmp rax,0x30
+	cmp rax,0x43
 	jmp .noswapgs
 	swapgs
 	.noswapgs:
@@ -42,22 +42,18 @@ section .text
 
 %macro popregs 0 
 	
-	add rsp, 8 ; cr2
+	add rsp, 24 ; cr2 gs fs
-	
+
 	pop rax
-	cmp rax,0x30
+	cmp rax,0x43
 	je .dontpopsegs
-	mov gs,rax
-	pop rax
-	mov fs,rax
-	pop rax
 	mov es,rax
 	pop rax
 	mov ds,rax
 	swapgs
 	jmp .poprest
 	.dontpopsegs:
-	add rsp,24
+	add rsp,8 ; ds
 	
 	.poprest:
 	pop rax

src/arch/x86_64/kstack.c

@@ -5,4 +5,5 @@
 void arch_setkernelstack(void* stack){
 	
 	arch_getcls()->ist.rsp0 = (uint64_t)stack;
+	arch_getcls()->kstack = stack;
 }

src/arch/x86_64/regs.c

@@ -1,4 +1,17 @@
 #include <arch/regs.h>
+#include <arch/msr.h>
+
+void arch_regs_saveextra(arch_extraregs* regs){
+	// user gs was swapped
+	regs->gsbase = rdmsr(MSR_KERNELGSBASE);
+	regs->fsbase = rdmsr(MSR_FSBASE);
+}
+
+void arch_regs_setupextra(arch_extraregs* regs){
+	// gs will be swapped later
+	wrmsr(MSR_KERNELGSBASE, regs->gsbase);
+	wrmsr(MSR_FSBASE, regs->fsbase);
+}
 
 void arch_regs_setupkernel(arch_regs* regs, void* ip, void* stack, bool interrupts){
         regs->rip = ip;

src/arch/x86_64/syscall.asm

@@ -0,0 +1,76 @@
+section .rodata
+
+
+extern syscall_libc_log
+func_count equ 1
+
+
+func_table:
+	dq syscall_libc_log
+
+section .text
+global asm_syscall_entry
+
+; the registers for the system call are:
+; RETURN:
+; rax -> ret value
+; rdx -> errno
+; PARAM:
+; rax -> func
+; rdi, rsi, rdx, r10, r8, r9 -> parameters
+; clobbers: rax, rdx, rcx, r11
+
+asm_syscall_entry:
+	swapgs
+
+	xchg rsp, [gs:0] ; get new stack
+	push qword [gs:0] ; save old stack
+	mov [gs:0], rsp ; return back the kernel stack
+	add qword [gs:0], 8 ; fix it
+
+	push rcx ; old rip
+	push r11 ; old rflags
+	
+	mov r11, 0x30 ; kernel data
+	mov ds, r11
+	mov es, r11
+
+	; save C scratch registers
+	; rax is not saved because it will be the return value
+	; rdx is not saved because it will be the errno value
+
+	push rdi
+	push rsi
+	push rcx
+	push r8
+	push r9
+	push r10
+	
+	; system V C abi expects the third param to be in rcx
+	; but the param is in rdx because of the syscall instruction
+
+	mov rcx, rdx
+
+	call [func_table + rax * 8]
+
+	; now restore the scratch registers
+
+	pop r10
+	pop r9
+	pop r8
+	pop rcx
+	pop rsi
+	pop rdi
+	
+	; restore entry state
+
+	mov r11, 0x40 ; user data
+	mov es,r11
+	mov ds,r11
+
+	pop r11
+	pop rcx
+	pop rsp
+	swapgs
+
+	o64 sysret

src/include/kernel/sched.h

@@ -23,6 +23,7 @@ typedef struct _thread_t{
 	struct _thread_t* prev;
 	struct _proc_t* proc;
 	arch_regs* regs;
+	arch_extraregs extraregs;
 	state_t state;
 	void* kernelstack;
 	void* kernelstackbase;

src/include/kernel/syscalls.h

@@ -0,0 +1,11 @@
+#ifndef _SYSCALLS_H_INCLUDE
+#define _SYSCALLS_H_INCLUDE
+
+typedef struct {
+        long ret;
+        long errno;
+} syscallret;
+
+syscallret syscall_libc_log(char* str);
+
+#endif

src/sys/Makefile

@@ -1,5 +1,5 @@
 objects := $(patsubst %.c,%.o,$(wildcard *.c))
-subdirs := mm sched
+subdirs := mm sched syscalls
 OBJPATH=$(OBJDIR)
 export
 

src/sys/sched/scheduler.c

@@ -162,9 +162,9 @@ void sched_timerhook(arch_regs* regs){
 
 	spinlock_release(&running.lock);
 
-
+	
 	memcpy(current->regs, regs, sizeof(arch_regs));
-
+	arch_regs_saveextra(&current->extraregs);
 
 	spinlock_acquire(&currentqueue->lock);
 
@@ -198,6 +198,8 @@ static void switch_thread(thread_t* thread){
 
 	arch_setkernelstack(thread->kernelstack);
 
+	arch_regs_setupextra(&thread->extraregs);
+	
 	arch_switchcontext(thread->regs);
 	
 	__builtin_unreachable();
@@ -291,6 +293,8 @@ void sched_runinit(){
 		printf("ELF load error: %s\n", strerror(ret));
 		_panic("Could not load init", 0);
 	}
+	
+	thread->extraregs.gsbase = 0xFFFFFFFFDEADBEEF;
 
 	switch_thread(thread);
 	

src/sys/syscalls/Makefile

@@ -0,0 +1,12 @@
+objects := $(patsubst %.c,%.o,$(wildcard *.c))
+subdirs :=
+OBJPATH=$(OBJDIR)
+export
+
+all: $(subdirs) $(objects)
+	for subdir in $(subdirs) ; do $(MAKE) -C $${subdir} ; done
+
+%.o: %.c
+	$(CC) $(CFLAGS) -o $@ $<
+	mkdir -p $(OBJPATH) 
+	cp $@ $(OBJPATH)/$@

src/sys/syscalls/libclog.c

@@ -0,0 +1,29 @@
+#include <kernel/syscalls.h>
+#include <kernel/alloc.h>
+#include <errno.h>
+#include <string.h>
+#include <stdio.h>
+
+syscallret syscall_libc_log(char* str){
+	
+	syscallret ret;
+
+	char* buf = alloc(strlen(str) + 1);
+	if(!buf){
+		ret.errno = ENOMEM;
+		ret.ret = -1;
+		return ret;
+	}
+
+	strcpy(buf, str);
+
+	printf("%s", str);
+
+	ret.errno = 0;
+	ret.ret = 0;
+
+	free(buf);
+
+	return ret;
+	
+}