Adjust stivale2 SMP spec a little to add an extra argument to the smp_info struct

STIVALE2.md

@@ -378,8 +378,10 @@ This tag reports to the kernel info about the firmware.
 struct stivale2_struct_tag_smp {
     uint64_t identifier;        // Identifier: 0x34d1d96339647025
     uint64_t next;
-    uint64_t cpu_count;         // Total number of logical CPUs (including BSP)
-    struct stivale2_smp_info smp_info[];
+    uint64_t cpu_count;         // Total number of logical CPUs (excluding BSP)
+    struct stivale2_smp_info smp_info[];  // Array of smp_info structs, one per
+                                          // additional logical processor, note
+                                          // that the BSP does not have one.
 } __attribute__((packed));
 ```
 
@@ -405,5 +407,10 @@ struct stivale2_smp_info {
                                  // is handed off.
                                  // All general purpose registers are cleared
                                  // except ESP/RSP, and RDI in 64-bit mode.
+    uint64_t extra_argument;     // This field is here for the kernel to use
+                                 // for whatever it wants. Writes here should
+                                 // be performed before writing to goto_address
+                                 // so that the receiving processor can safely
+                                 // retrieve the data.
 } __attribute__((packed));
 ```

stage2/sys/smp.c

@@ -89,7 +89,7 @@ struct smp_information *init_smp(size_t   *cpu_count,
     asm volatile ("sgdt %0" :: "m"(gdtr));
 
     struct smp_information *ret = balloc_aligned(0, 1);
-    *cpu_count = 1;
+    *cpu_count = 0;
 
     // Parse the MADT entries
     for (uint8_t *madt_ptr = (uint8_t *)madt->madt_entries_begin;

stage2/sys/smp.h

@@ -11,6 +11,7 @@ struct smp_information {
     uint32_t lapic_id;
     uint64_t stack_addr;
     uint64_t goto_address;
+    uint64_t extra_argument;
 } __attribute__((packed));
 
 struct smp_information *init_smp(size_t   *cpu_count,

stage2/sys/smp_trampoline.asm

@@ -100,8 +100,8 @@ parking32:
   .out:
     mov esp, dword [edi + 8]
     push 0
-    push eax
     push edi
+    push eax
     xor eax, eax
     xor ebx, ebx
     xor ecx, ecx

stivale/stivale2.h

@@ -136,6 +136,7 @@ struct stivale2_smp_info {
     uint32_t lapic_id;
     uint64_t target_stack;
     uint64_t goto_address;
+    uint64_t extra_argument;
 } __attribute__((packed));
 
 struct stivale2_struct_tag_smp {