write syscall functions

2 files changed, 101 insertions, 22 deletions

diff --git a/boot/fake_syscall_entry.S b/boot/fake_syscall_entry.S
index 9daa0d5..f75c2d7 100644
--- a/boot/fake_syscall_entry.S
+++ b/boot/fake_syscall_entry.S
@@ -5,17 +5,7 @@
 
 .extern fake_syscall_handler
 
-fake_syscall_start:
-	cli
-	mov %rdi, %rsp
-	jmp .L_fake_syscall_return
-
 /*
-	Fake syscall mechanism
-
-	The Kjarna kernel runtime loader/linker is started by the Kjarna boot kernel and supported
-	by a subset of system calls in order to load files and place them in virtual memory.
-
 	SYSCALL STACK FRAME - FROM LOWER TO HIGHER ADDRESS
 
 	0	pad
@@ -34,6 +24,11 @@ fake_syscall_start:
 	104 state.return_cs
 */
 
+fake_syscall_start:
+	cli
+	mov %rdi, %rsp
+	jmp .L_fake_syscall_return
+
 fake_syscall_entry:
 	sub $112, %rsp
 	mov %rax, 8(%rsp)
diff --git a/boot/main.c b/boot/main.c
index 611c833..ed18578 100644
--- a/boot/main.c
+++ b/boot/main.c
@@ -5,6 +5,7 @@
 #include <bits/x86_64/descriptor.h>
 #include <libc/stdio.h>
 #include <posix/sys/mman.h>
+#include <posix/unistd.h>
 
 /*
  * Fake syscall mechanism -
@@ -47,32 +48,114 @@ static struct segment_descriptor const fake_syscall_gdt[] =
 
 typedef uint64_t syscall_delegate_parameters[6];
 
+static struct
+{
+	uint16_t cs;
+	uint16_t ds;
+	uint64_t rflags;
+	struct descriptor_table_register_long gdtr;
+}
+uefi_context;
+
+static void save_uefi_context()
+{
+	__asm__ volatile (
+			"movw %%cs, %0\n"
+			"movw %%ds, %1\n"
+			"pushfq\n"
+			"popq %3\n"
+			"sgdt %2\n"
+			:
+				"=m"(uefi_context.cs),
+				"=m"(uefi_context.ds),
+				"=m"(uefi_context.gdtr),
+				"=g"(uefi_context.rflags)
+			:
+		);
+}
+
+static void restore_uefi_context()
+{
+	__asm__ volatile (
+			"lgdt %0\n"
+			"mov %w1, %%ds\n"
+			"mov %w1, %%es\n"
+			"mov %w1, %%fs\n"
+			"mov %w1, %%gs\n"
+			"mov %w1, %%gs\n"
+			"mov %w1, %%ss\n"
+			"push %q2\n"
+			"lea .Lflush(%%rip), %%rax\n"
+			"push %%rax\n"
+			"lretq\n"
+			".Lflush:\n"
+			"push %q3\n"
+			"popfq\n"
+			:
+			:
+				"m"(uefi_context.gdtr),
+				"m"(uefi_context.ds),
+				"m"(uefi_context.cs),
+				"g"(uefi_context.rflags)
+			:
+				"rax"
+			);
+
+}
+
 struct syscall_context_return_state
 {
-	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
+	uint64_t rflags;
+	struct descriptor_table_register_long gdtr;
+	uint64_t return_ds;
+	uintptr_t return_rip;
+	uint64_t return_cs;
 };
 
 struct syscall_context
 {
-	uint64_t pad; // 8
-	uint64_t syscall_index; // 16
-	syscall_delegate_parameters parameters; // 64
+	uint64_t pad;
+	uint64_t syscall_index;
+	syscall_delegate_parameters parameters;
 	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];
+int64_t syscall_delegate_write(syscall_delegate_parameters params)
+{
+	return write((int)params[0], (void *)params[1], (size_t)params[2]);
+}
+
+constexpr int NR_SYSCALLS = 10;
+static syscall_delegate *syscall_handler_delegates[NR_SYSCALLS] =
+{
+	nullptr,
+	syscall_delegate_write
+};
 
 SYSV_ABI int64_t fake_syscall_handler(struct syscall_context *context)
 {
-	(void)context;
-	return -1;
+	if (context->syscall_index > NR_SYSCALLS)
+	{
+		// TODO: ENOSYS
+		return -1;
+	}
+
+	syscall_delegate *delegate = syscall_handler_delegates[context->syscall_index];
+
+	if (delegate == nullptr)
+	{
+		// TODO: ENOSYS
+		return -1;
+	}
+
+	restore_uefi_context();
+	int64_t result = delegate(context->parameters);
+	save_uefi_context();
+	
+	return result;
 }
 
 SYSV_ABI void fake_syscall_entry(void);
@@ -117,6 +200,7 @@ int main(int argc, char **argv)
 	struct kjarna_boot_image boot_image = get_boot_image();
 	install_syscall_handler();
 	void *fake_syscall_stack = create_fake_syscall_stack((void *)boot_image.entry);
+	save_uefi_context();
 	fake_syscall_start(fake_syscall_stack);
 }