feat: SMP stage 1 (4 harts, per-hart guarded stacks, home-core affinity, IPIs, TLB shootdown, one temporary kernel lock), 4-core storm

crates/adapter-riscv/linker.ld

@@ -46,15 +46,13 @@ SECTIONS {
         _bss_end = .;
     }
 
-    /* Left unmapped, so overflowing the kernel stack faults instead of
-       silently overwriting .bss. */
+    /* One kernel stack per hart (smp::MAX_HARTS, smp::STACK_SLOT): each
+       slot is an unmapped guard page, so overflowing a stack faults
+       instead of silently overwriting what lies below, then the stack. */
     . = ALIGN(4096);
-    _stack_guard = .;
-    . += 4096;
-
-    _stack_bottom = .;
-    . += 0x80000;
-    _stack_top = .;
+    _stacks_start = .;
+    . += 8 * (4096 + 0x80000);
+    _stacks_end = .;
 
     _heap_start = .;
 }