Record networking and DMA development progress

Add the current OS source tree, build scripts, system image layout, and development notes covering DMA page allocation, e1000 bring-up, net API dispatch, and DHCP work in progress.

CODE/UTSM/arch/x86_64/idt_stubs.S

@@ -0,0 +1,62 @@
+/* IDT assembly stubs — SAS-R0 interrupt vectors */
+.section .text
+
+.macro isr_no_err n
+.global isr_stub_\n
+.type isr_stub_\n, @function
+isr_stub_\n:
+    pushq $0
+    pushq $\n
+    jmp isr_common
+.endm
+
+.macro isr_err n
+.global isr_stub_\n
+.type isr_stub_\n, @function
+isr_stub_\n:
+    pushq $\n
+    jmp isr_common
+.endm
+
+/* Exceptions 0-31 */
+isr_no_err 0;  isr_no_err 1;  isr_no_err 2;  isr_no_err 3
+isr_no_err 4;  isr_no_err 5;  isr_no_err 6;  isr_no_err 7
+isr_err    8;  isr_no_err 9;  isr_err    10; isr_err    11
+isr_err    12; isr_err    13; isr_err    14; isr_no_err 15
+isr_no_err 16; isr_err    17; isr_no_err 18; isr_no_err 19
+isr_no_err 20; isr_no_err 21; isr_no_err 22; isr_no_err 23
+isr_no_err 24; isr_no_err 25; isr_no_err 26; isr_no_err 27
+isr_no_err 28; isr_no_err 29; isr_err    30; isr_no_err 31
+
+/* IRQ 32-47 */
+isr_no_err 32; isr_no_err 33; isr_no_err 34; isr_no_err 35
+isr_no_err 36; isr_no_err 37; isr_no_err 38; isr_no_err 39
+isr_no_err 40; isr_no_err 41; isr_no_err 42; isr_no_err 43
+isr_no_err 44; isr_no_err 45; isr_no_err 46; isr_no_err 47
+
+/* Common ISR */
+isr_common:
+    pushq %rdi
+    pushq %rsi
+    pushq %rdx
+    pushq %rcx
+    pushq %rax
+    pushq %r8
+    pushq %r9
+    pushq %r10
+    pushq %r11
+
+    movq %rsp, %rdi
+    call idt_handler
+
+    popq %r11
+    popq %r10
+    popq %r9
+    popq %r8
+    popq %rax
+    popq %rcx
+    popq %rdx
+    popq %rsi
+    popq %rdi
+    addq $16, %rsp
+    iretq