Pass the virtual page offset for the kernel to kernel.Kmain

Ths page offset is defined in arch/XXX/constants.inc and needs to be
passed to the kernel so we can correctly calculate the physical frame
addresses that correspond to the ELF section virtual memory addresses.

src/arch/x86_64/asm/rt0_64.s

@@ -51,6 +51,8 @@ _rt0_64_entry:
 	extern _kernel_end
 	extern kernel.Kmain
 	
+	mov rax, PAGE_OFFSET
+	push rax
 	mov rax, _kernel_end - PAGE_OFFSET
 	push rax
 	mov rax, _kernel_start - PAGE_OFFSET

src/gopheros/kernel/kmain/kmain.go

@@ -20,18 +20,19 @@ var (
 // allocated by the assembly code.
 //
 // The rt0 code passes the address of the multiboot info payload provided by the
-// bootloader as well as the physical addresses for the kernel start/end.
+// bootloader as well as the physical addresses for the kernel start/end. In
+// addition, the start of the kernel virtual address space is passed to the
+// kernelPageOffset argument.
 //
 // Kmain is not expected to return. If it does, the rt0 code will halt the CPU.
 //
 //go:noinline
-func Kmain(multibootInfoPtr, kernelStart, kernelEnd uintptr) {
+func Kmain(multibootInfoPtr, kernelStart, kernelEnd, kernelPageOffset uintptr) {
 	multiboot.SetInfoPtr(multibootInfoPtr)
 
 	var err *kernel.Error
 	if err = allocator.Init(kernelStart, kernelEnd); err != nil {
 		panic(err)
-	} else if err = vmm.Init(); err != nil {
 		panic(err)
 	} else if err = goruntime.Init(); err != nil {
 		panic(err)

src/gopheros/stub.go

@@ -11,5 +11,5 @@ var multibootInfoPtr uintptr
 // A global variable is passed as an argument to Kmain to prevent the compiler
 // from inlining the actual call and removing Kmain from the generated .o file.
 func main() {
-	kmain.Kmain(multibootInfoPtr, 0, 0)
+	kmain.Kmain(multibootInfoPtr, 0, 0, 0)
 }