this is starting to work

4 files changed, 114 insertions, 55 deletions

diff --git a/api/bits/x86_64/descriptor.h b/api/bits/x86_64/descriptor.h
index 649ac74..c0c00f6 100644
--- a/api/bits/x86_64/descriptor.h
+++ b/api/bits/x86_64/descriptor.h
@@ -4,7 +4,7 @@ struct descriptor_table_register_long
 {
 	uint16_t limit;
 	uint64_t base;
-} __attribute__((packed, aligned(16)));
+} __attribute__((packed, aligned(8)));
 
 struct segment_descriptor
 {
diff --git a/boot/fake_syscall_entry.S b/boot/fake_syscall_entry.S
index bc175c1..8a3f8c8 100644
--- a/boot/fake_syscall_entry.S
+++ b/boot/fake_syscall_entry.S
@@ -1,34 +1,79 @@
 .section .text
 
 .global fake_syscall_entry
-.global fake_syscall_return
+.global fake_syscall_start
 
 .extern fake_syscall_handler
 
-fake_syscall_entry:
-	hlt;
-
-fake_syscall_return:
+fake_syscall_start:
 	cli
-fake_syscall_swap:
-	mov %cs, %rax
-	pushq %rax
-	pushq %rdx
-	mov %ds, %rax
-	pushq %rax
-	sub $16, %rsp
-	sgdt (%rsp)
-	mov %rsp, (%rsi)
 	mov %rdi, %rsp
-	lgdt (%rsp)
-	add $16, %rsp
-	movw (%rsp), %ds
-	movw (%rsp), %es
-	movw (%rsp), %fs
-	movw (%rsp), %gs
-	movw (%rsp), %ss
+	jmp .L_fake_syscall_return
+
+/*
+	SYSCALL STACK FRAME - FROM LOWER TO HIGHER ADDRESS
+
+	0	pad
+	8	syscall_index
+	16	parameters[0]
+	24  parameters[1]
+	32  parameters[2]
+	40  parameters[3]
+	48  parameters[4]
+	56  parameters[5]
+	64  state.rflags
+	72  state.gdtr.base:2 state.gdtr.limit:6
+	80  state.gdtr.limit:2 [unused]:6
+	88  state.return_ds
+	96  state.return_rip
+	104 state.return_cs
+*/
+
+fake_syscall_entry:
+	sub $112, %rsp
+	mov %rax, 8(%rsp)
+	mov %rdi, 16(%rsp)
+	mov %rsi, 24(%rsp)
+	mov %rdx, 32(%rsp)
+	mov %r10, 40(%rsp)
+	mov %r8, 48(%rsp)
+	mov %r9, 56(%rsp)
+
+	pushfq
+	pop %rdi
+	mov %rdi, 64(%rsp)
+
+	sgdt 72(%rsp)
+	movw %ds, 88(%rsp)
+	mov %rcx, 96(%rsp)
+	movw %cs, 104(%rsp)
+
+	mov %rsp, %rdi
+	call fake_syscall_handler
+
+	push %rbp
+	mov %rsp, %rbp
+	add $64, %rsp
+	popfq
+	mov %rbp, %rsp
+	pop %rbp
+
+.L_fake_syscall_return:
+	lgdt 72(%rsp)
+	mov 88(%rsp), %rdi
+	mov %di, %ds
+	mov %di, %es
+	mov %di, %fs
+	mov %di, %gs
+	mov %di, %ss
 
-	add $8, %rsp
+	mov 16(%rsp), %rdi
+	mov 24(%rsp), %rsi
+	mov 32(%rsp), %rdx
+	mov 40(%rsp), %r10
+	mov 48(%rsp), %r8
+	mov 56(%rsp), %r9
 
+	add $96, %rsp
 	lretq
 
diff --git a/boot/main.c b/boot/main.c
index d217235..12b411c 100644
--- a/boot/main.c
+++ b/boot/main.c
@@ -3,6 +3,8 @@
 #include <asm/x86_64/msr.h>
 #include <bits/x86_64/msr.h>
 #include <bits/x86_64/descriptor.h>
+#include <libc/stdio.h>
+#include <posix/sys/mman.h>
 
 /*
  * Fake syscall mechanism -
@@ -43,15 +45,39 @@ static struct segment_descriptor const fake_syscall_gdt[] =
 	{ 0xffff, 0, 0, 0x92, 0xcf, 0}
 };
 
-SYSV_ABI static void fake_syscall_handler(void)
+typedef uint64_t syscall_delegate_parameters[6];
+
+struct syscall_context_return_state
 {
-	while (true);
-}
+	uint64_t rflags; // 8
+	struct descriptor_table_register_long gdtr; // 24
+	uint64_t return_ds; // 32
+	uintptr_t return_rip; // 40
+	uint64_t return_cs; // 48
+};
+
+struct syscall_context
+{
+	uint64_t pad; // 8
+	uint64_t syscall_index; // 16
+	syscall_delegate_parameters parameters; // 64
+	struct syscall_context_return_state state;
+};
+
+typedef int64_t (syscall_delegate)(syscall_delegate_parameters params);
+
+//constexpr int NR_SYSCALLS = 10;
+//static syscall_delegate *syscall_handler_delegates[NR_SYSCALLS];
 
-static void *return_rsp;
+SYSV_ABI int64_t fake_syscall_handler(uint64_t syscall_index, struct syscall_context *context)
+{
+	(void)syscall_index;
+	(void)context;
+	return -1;
+}
 
 SYSV_ABI void fake_syscall_entry(void);
-SYSV_ABI void fake_syscall_return(void *target_rsp, void **return_rsp, SYSV_ABI void (*callback)());
+SYSV_ABI void fake_syscall_start(void *stack);
 
 static void install_syscall_handler(void)
 {
@@ -66,37 +92,24 @@ static void install_syscall_handler(void)
 	msr_write(MSR_INDEX_EFER, efer);
 }
 
-struct context_stack_frame
-{
-	struct descriptor_table_register_long lret_gdtr;
-	uint64_t lret_ds;
-	uint64_t lret_rip;
-	uint64_t lret_cs;
-};
-
-static void enter_boot_image(struct kjarna_boot_image *image)
+static void *create_fake_syscall_stack(void *entry_addr)
 {
-	size_t boot_stack_size = 0x10000;
-	char *boot_image_stack = calloc(1, boot_stack_size);
-	void *boot_image_stack_head = boot_image_stack + boot_stack_size;
+	constexpr size_t fake_syscall_stack_size = 0x20000; // 128KiB stack
+	char *stack_pointer_base = mmap(nullptr, fake_syscall_stack_size, 0, 0, -1, 0);
+	void *stack_pointer_head = stack_pointer_base + fake_syscall_stack_size;
 
-	struct context_stack_frame *stack_frame = stack_alloc(&boot_image_stack_head, sizeof(*stack_frame));
+	struct syscall_context *context = stack_alloc(&stack_pointer_head, sizeof(*context));
 
-	stack_frame->lret_cs = 8;
-	stack_frame->lret_ds = 16;
-	stack_frame->lret_rip = (uintptr_t)image->entry;
+	context->state.rflags = 0;
+	context->state.gdtr.base = (uintptr_t)&fake_syscall_gdt;
+	context->state.gdtr.limit = sizeof(fake_syscall_gdt) - 1;
+	context->state.return_ds = 16;
+	context->state.return_cs = 8;
+	context->state.return_rip = (uintptr_t)entry_addr;
 
-	stack_frame->lret_gdtr.limit = sizeof(fake_syscall_gdt) - 1;
-	stack_frame->lret_gdtr.base = (uintptr_t)fake_syscall_gdt;
-
-	
-	fake_syscall_return(boot_image_stack_head, &return_rsp, fake_syscall_handler);
-
-	while (true);
+	return stack_pointer_head;
 }
 
-#include <libc/stdio.h>
-
 int main(int argc, char **argv)
 {
 	(void)argc;
@@ -104,6 +117,7 @@ int main(int argc, char **argv)
 
 	struct kjarna_boot_image boot_image = get_boot_image();
 	install_syscall_handler();
-	enter_boot_image(&boot_image);
+	void *fake_syscall_stack = create_fake_syscall_stack((void *)boot_image.entry);
+	fake_syscall_start(fake_syscall_stack);
 }
 
diff --git a/lldbscript b/lldbscript
index 3f94ba2..6d134f5 100644
--- a/lldbscript
+++ b/lldbscript
@@ -3,5 +3,5 @@ target modules add service/kjarna.os
 gdb-remote localhost:1234
 target modules load --file kjarna.efi .text 0x6184000 .data 0x6189000
 target modules load --file kjarna.os --slide 0x6178000
-b enter_boot_image
+b main