create and switch to new stack

src/x86_64/paging.c

@@ -1,5 +1,6 @@
 #include "std.h"
 #include "ram.h"
+#include "x86_64/address.h"
 #include "x86_64/asm.h"
 #include "x86_64/paging.h"
 
@@ -494,13 +495,21 @@ void pt_create_minimal(void) {
 
     // 16 GiB identity map with hugepages starting at low end of upper half of AS
     unsigned int npages_in_gb = 1ull << 18;
+    unsigned int npages_idmap = 16 * npages_in_gb;
     struct vpn vpn_idmap_start = vpn_from_aligned_va(va_from_value(1ull << 47));
     pt_map_range(vpn_idmap_start,
         ppn_from_pagenum(0),
-        16 * npages_in_gb,
+        npages_idmap,
         true, true, false,
         new_cr3);
 
+    // new stack with 4 GiB size and guard pages around
+    // TODO one stack for each core
+    struct vpn stack_virt = vpn_from_pagenum(vpn_to_pagenum(vpn_idmap_start) + npages_idmap + 1);
+    struct ppn stack_phys;
+    ASSERT(ram_alloc_frame_zeroed(&stack_phys, RAM_PAGE_NORMAL));
+    pt_map_single(stack_virt, stack_phys, true, true, false, new_cr3);
+
 #ifdef PT_CREATE_DEBUG
     uint64_t value = pa_to_value(pa_from_ppn(new_cr3));
     printf("new cr3: %p\n", value);
@@ -529,9 +538,18 @@ void pt_create_minimal(void) {
     set_cr3(value);
     set_identity_mapping(vpn_idmap_start);
 
+    // stack switch
+    // it doesn't really make sense to copy stack contents because rbp and pointers
+    // to local variables will point to the wrong location.
+    // this means we won't leave this function for now.
+    uint64_t new_sp = va_to_canonical(va_from_vpn(stack_virt)) + 4096;
+    __asm__("mov %0,%%rsp" ::"r"(new_sp));
+
 #ifdef PT_CREATE_DEBUG
     printf("hello from new page table!\n");
 #endif
+
+    PANIC("end of pt_create_minimal");
 }
 
 // --- iterators ---